JPRS ID: 9513 USSR REPORT PHYSICS AND MATHEMATICS

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- JPRS L/9513
29 January 1981
- USSR Report
PHYSICS AND MATHEMATICS
(FOUO 1 /81)
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JPRS I,/9513
29 January 1981
USSR REPORT
PHYSICS AND MATHEMATICS
(FOUO 1/81)
CONTENTS
LASERS AND MASERS
Photolysis Lasers for Controlled Nuclear Fusion
Chemical Lasers: New Results and Ideas
Abstracts From the Colllection 'OPTICALLY PUMPED GAS LASERS',........
A Pulse-Periodic Photodissociative Iodine Laser Pumped by the
Radiation of Magnetoplasma Compressors
Concerning the Change in Shielding Action of Products of Thermal
Dissociation of Materials Under the Effect of Laser Emission in
a Moving Medium
Pumping of Electron Beam-Controlled C02 Lasers With Maximum Beam
Utilization Factor
Energy Characteristics of a Copper Vapor Laser With Transverse
Discharge
Concerning the Possibility of Using Gasdynamic Pyrolysis for
Producing Lasing Media
Experimental Study of the Possibility of Effectively Coupling the
Energy Out of the Active Medium of a DF-C02 Amplifier of.Nano-
second Radiation Pulses...........................................
1
20
35
40
44
49
55
63
68
- a- [III - USSR - 21H S&T FOUO]
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LASERS AND MASERS
UDC 621.373.826.038.823
PHOTOLYSIS LASERS FOR CONTROLLED NUCLEAR FUSION
Moacow IZVESTIYA AKA.DEMII NAUK SSSR: SERIYA FIZICIiESKAYA in Russian Vol 44y No 10,
- Oct 80 pp 2002-2017
[Article by S. B. Kormer]
[Text] Introduction
A typical feature of photolysis lasers proposed in 1961 by the authors of Ref. 1
- is a rather wide band of absorption of pumping radiation (_103cm 1) similar to the
_ absorption band of solid-state lasers in combination with a narrow luminescence
line of 10'2-10-1 cm-1. This makes it possible to achieve high gains and a low
lasing threshold.
Lasing in thia type of laser was first attained [Ref. 2, 31 on molecules of CHgI
and C73I (RI +hv 4 R+ I*). Emission wavelength is a=1. 315 um. An energy of 1-5 mJ
was achieved. A rather cumbersome flash photolysis iodine laser was developed in
1966 [Ref . 4], giving a laser energy of 65 J for 1.5 ms.
SEimulated emission was reported in a Q-switched iodine laser in Ref. 5, although
it was not until 1971 that interest arose in such lasers for research in the field
of nuclear fusion, when Ref. 6 was published, the first of a large series of papers
on work at the Max-Planck Institute in Garching. In these papers, on the basis of
reaearch resulr_s, the iodine laser was offered as one of the possible competitors
of neodymium and C02 lasers for controlled nuclear fusion. Possibilities of using
iodine lasers for these purposes were explored by Soviet [Ref. 7, 8], U. S. [Ref.
9, 10] and British [Ref. 11] scientists*.
Outside of the Soviet Union, the best results have been attained at Max-Planck In-
stitute. For example it was reported in Ref. 12 that an energy of 300 J was at-
tained in a pulse with duration of (1-3)�10-9 s withefficiency of - 0.1% with re-
spect to the energy stored in a capacitive accumulator. In the brief paper of Ref.
13 mention is made of attainment of 500 J 3t Ti = 0.5�10-9 s. In the USSR the maxi-
mum energies that have been attained in the period up to publication of the present
report have been - 300 J in 10'9 s at an efficiency of 0.1% [Ref. 14] and 500 J in
1.5�10-9 s at the same Efficiency [Ref. 15]. However, these figures are far from
exhausting the capabilities of iodine lasers. For example, specialists at the
Max-Planck Institute are af the opinion that there is a real possibility of making
*Here and belaw we cite only the first papers by the different authors.
1
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iodine lasers with pulse energy of 10-100 kJ at a duration of 0.1 ns and with a
pulse recurrence rate of 100 Hz. ~
Among the advantsges of iodine lasers, mention should be made of t:he following.
1. Capability of fairly uniform circulation of large cross sections of working
- fluid, and in this way giving large energies in a single beam, which enablea selec-
tion of the optimum number of active elements of a laser facility for given energy.
2. Capability of regulating the width of the luminescence line of the working tran- _
sition by adding a buffer gas. This enables optimization of gain of the lasex
medium and duration of the lasing pulse. At atmospheric pressure it is possible to
amplify pulses with T> 40-100 ps [Ref. 17].
3. Comparatively long lifetime of the excited iodine and comparatively short pump-
ing duratian, which reduces the intensity of superluminescence.
4. Comparatively minor optical inhomogeneities of the working medium and capability
of achieving relatively small divergence of emission.
- 5. Fewer limitations associated with, radiatian strength of the working medium (self-
' focusing and the like).
These advantages of the iodine laser put it on the same level [Ref. 18, 19] with
' more perfected neodymium lasers and C02 gas lasers.
In this paper we give our principal attention to a survey of the results realized
in our own research [Ref. 8, 15, 20-291.
1. Workj.ng fluida and processes. Estimation of aiitput energy of amplifiers
- The most estensively used working fluids for iodine lasers are the organic iodides
CFgI and C3F7I. The absorption band of these compounds has a maximum at XmaX x 270
nm with half-amplitude width of about 35 nm. The absorption cross section at the
- mRximum is (6-8)�10-19 cm2, which corresponds to an absorption coefficient az.2�10-2
(torr�cm)-1. The relatively low coefficient of absurption enables fairly uniform
circulation through working volumos with a large aperture.
lipon absorption of an ultraviolet quantum, the working fluid dissociates into a
- radical and an electronically exciiced iodine atom:
C,F; I+ hv, -C,F,+ I' ('P.,,) .
Studies have shewn that the quantum yield in this case is cl ose to u nit y. The
laser transition is between levels 2P1/2 and 2P% of the iodine atom, which have a
hyperfine structure [Ref. 30, 31]. The resultant laser emission wavelength is
1.315 um.
One of the distinguishing features of Lhe given active media is the capability of
varying the amplification cross section Q over a rather wide range by adding buffer
gases such as C02, SF6, Ar and others. When this is done, the cross section cr
2
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decreases with increasing partial pressure of both the working fluid itself and
the buffer gases [Ref. 17]. This increases the latitude of development of iodine
lasers since it gives a means of attair..ing relatively low weak-signal gains at high
specific densities of the stored and output energies.
- The expected energy paramr:ters of each of the amplifiers with assumption of uniform
population inveraion over its cross section and lengthwise can be determined from
_ an expresaion [Ref. 32] that describQa the amplif ication process:
E~yj=G.,~ln(K,(eaP -i~+
Et1C
ho�exp o,+NL, (2)
- hv 24 !iv
Euac = (3)
a� -i-
31 a,.
~ g, .
Here eeX and eeb4x are respectively the density of the input and output eaergies of
the amplifier; Kp is the weak-signal gain; 034 is the amplification cross section
on transition FB = 3-FH= 4; N is the initial population of excited particles on the
sublevel with quantum number FB = 3; L is the length of the amplifier; eHac is the
saturation energy of the working transition FB = 3-*FH = 4; ge and gH are the sta-
tistical weights of the upper and lower sublevels participating in the transition.
-J For the sake of simplicity, relations (2) and (3) are g;-qen for the most frequently
' encountered case where the lasing transition is between r_he sublevel with quantum
- number FB = 3 of level 2P1 , , 2 and sublevel FH = 4 of level 2F3/2. It was also taken
into consideration that in accordance with Ref. 31 the upper sublevels in the case
of interest to us T< 10-9 s do not have time to relax relative to one another,
while the sublevels of level 2P3,2 do have time. Then gg = 7, gH = 24.
In the limiting case when eBX� EeEAx, (1) implies
E.ti:. op.s �.,c ln Ro+e..,. (4)
From (2)-(4) we get
24 i4 e
31 hvt1~'L = 31 3an. oo: s, (S)
where
~
e o,-..-.~:v1'aL, :1'=--g, -N= 12 N.
- g.-3 7
The total stored energy e3an. nonH on level 2P1/2, which must be known for calcu-
iating the output energy from (5), can be found from the free lasing energy
- Ece. reH� In the approximation of fairly rapid "cleaninp," of the lower lasing
3
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~ level (2P1,2) as a result of recombination of an unexcited iodine atom with a radi-
cal ILRef. 17]
E3au. ao:ta-Zcx ia+Enopr
where enoP is the threshold energy.
In designing an amplifier that operates in the monopulse mode, when the input sig-
nal is applied at the instant of the first zero of the pwn.ping current to prevent _
the influence that the uncompensated magnetic field of the pumping sources has on =
the spectrum of the hygerfine structure of atomic iodine, it is necessary to take
consideration only of the energy that has been stored up to this instant:
~
E3ae yoso- ~ l /e',. reaTeaa; ' 7)
where Y is the fraction of the stored energy on level 2P1/2 by the instant of arri-
val of the monopulse.
Experimental seudies of the time dependF:nce of lasing power have shown that the
first half-period of the current of the.� final amplifiers contains about 70% of the
= energy stored in the accumulator. The.refore the value of E3an. MoHOfrom (7) must
_ be used in (5).
If we know the stored energy on the working sublevel, we can f ind the amplification
cross section that ensures a given weak-signal gain. The necessary value of Q34
is attained by varying the buffer gas and its pressure [Ref. 17]:
- 7 (8)
- - = t, - Y e.pi,
a,, ~
,
where Bp is the Doppler component of luminescence line broadening, ai is the coef-
ficient of collisional broadening of the different gases at psessure [Pi]�
The permissible values of Kp in amplifiers depend on a number of factors such as
the optical decoupling mechanisms that are used, the presence of vacuum selectcrs,
parasitic reflectors and the like. Experience has shown that in order to avoid
self-excitation of amplifiers, Ko must be kept to the order of 102 or less, par-
ticularly in the final amplifiers.
In Section 5 on the basis of the relations given above, estimates of the output
energy of amplifiers are made and compared with experimental rzsults.
2. Concerning the degree of uniformity of pumping and the optical homogeneity of
the working medium in an iodine laser
In extensive use for pumping iodine lasers are both flashlamps [Ref. 4, 6, 8, 33,
34] and an open electric discharge in the working mixture. The author.s of Ref. 7,
35, 36 used an exploding wire to initiate discharge in a gas. We utilized reusable
large-aperture discharge pumping sources with traveling discharge propo�ed and de-
veloped by the authors of [Ref. 15] in our amplifiers.
4
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a. o.'",, ed(relative units)
' a a
i

I

_.J-1--J-
4 a ia
0.8 ~ bb
1
r
- (1, 4 � ~
~

~
~
D ~ ~
Q ~l6
i B c

_
.
= I
{
tm
k'ig. 1
a a
T f~ S ~
~ .1 / 1 / l II QO
d,l0-I6cm�i 0 10 ZO JO RcM
L-- j ~
12
a
5
~ s
i4
v '
6 !6
Fig. 2
~
~
/
6b
~ Z4 R, cnr
Fig. 1. Distribution of inversion with respect to radius of the cell (broken lines
_ shaw the calculation, solid lines show the experiment): a--lamp source (pC3F7I 22
5;nm Hg); b--electric discharge source (pC 3F7 i = 5 mm Hg); c--exploding wire
(PC3F7I = 7.5 mm Hg)
Fig. 2. a--Isolines of population inversion; b--distribution of inversion with
_ respect to radius of the cell with pumping by one or more sources. Calculation:
- dotted lines--1 source; solid lines--9 sources; broken line--40 sources; 1, 2, 3,
- 4, 6--pC3F7i = 4.5 mm Hg; S, 7--3 mm Hg. Experiment: points--9 sources, pp=3 mm Hg
Fig. 1 shows the results of a study of uniformity of circulation through the work-
ing volume of a large-aperture laser when a lamp source or electric discharge
source [Ref. 15, 37] is placed on the axis of the cell. The experimental value of
the dependence of inversion A on radius R is determined either directly or from the
_ distribution of free la:iing over the end face. The behavior of A(R) observed with
pumping by different sources is determined not only by the absorption of quanca in
the working medium,but also by.purely geometric reduction of the density of quarta
with increasing radius.
_ The nonuniformity of inversion distribution can be reduced by reducing the partial
pressure of the working mixture, and also by increasing the number of pumping
5
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~
sources in the working volume. The latter approach is especially necessary for
making large-aperture amplifiers (see Fig. 2a). Optimization of the number of
sources and the radius of their configuration was done by a special program of two-
dimenaional calculation of photodissociation. 1'his program accounts for the ttme
dependence of the brightness temperature of the source Tbr(t) and the actual pro-
file of the abeorption band of the working fluid. The program is also suitable for
calculation of electrodisctiarge pumping sources with expanding emission surface.
The results of some calculations are shown in Fig. 2b, where the radial distribu-
- tion of inversion is shown with var{.ation of the radius of source placement, the
- number of sources and the partial pressure of the working fluid. We can see that
if a single source is placed in a cell with Rp = 20 cm (curves 1 and 2), the inver-
sion differential at pp = 4.5 mm Hg of C3F7I will exceed 15. On the other hand, if
about 40 sources or more are placed on the outer sutface of the cell, inversion
will be nearly uniform over the entire cross section (curve 3). When the number of
sources is reduced to 9(curves 4, S, 6 and 7), the difference in inversion in-
creases. For example if tY:i- sources are placed at Rp = 22.5 cm, this difference
= reacties a factor of 1.5-2 at pp = 4.5 r~,.-n Hg, and a factor of 1.3-1.5 at pp = 3 mm Hg
(curves 4 and 5).
As we can see from the figure, the experimentally-found distribution of inversion
in free lasing runs agrees fairly well with calculated results (curve 5).
The degree of inversion nonuniformity with respect to angle with nine sources can
be seen from Fig. 2a, which gives the pattern of isolines of population inversion
at pp(C3F7I) '4.5 mm Hg and Rp = 27.5 cm. Angular nonuniformity shows up at Rp> 15
cm and increases as.the sources are approached. The maximum nonuniformity of in-
version density with respect to angle for the given arrangement is 30�6.
On the basis of experiments and the results of theoretical optimization we have now
- decided that in future research we will use nine reusable traveling-discharge
sources placed at Rp = 22.5 cm. The optical inhomogeneity of the active medium has
been studied experimentally f.or these conditions. Similar studies have also been
- done for amplifiers with flashlamp pumping in which the active medium was contained
- i.n quartz cells. (A more detailed description of the amplifiers will be given
- be]_ow. )
Measurements were made in the driven mode of amplifier operation close to the pump-
ing sources, where optical inhomogeneities should be maximum. The amplifier medium
to be studied was placed in one of the arms of a Michelson interferometer. The
studies were done on a wavelength of 0.63 um, analogously to the way that this had
been done previously [Ref. 22, 24-27, 36] (see also Ref. 38). The gradient of the
_ index of refraction and its dependence on distance r from the pumping source were
determined from the profile of the inde:c of refraction of the medium found at the
inatant of zero current.
The resultant curves of grad n= f(r) for the working media of three amplifiers are
_ shown in Fig. 3. We can see that in all amplifiers grad n decreases with increas-
ing distance from the pumping source. The width of the zone of optical inhomo-
geneities is 1.5-2 cm. Increasing the pressure of the working fluid (C3F7I) in
the amplifiers leads to an increase in grad n. At the same time, the absolute
- values of grad n are such as to enable attainment of good divergence. For example,
6
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9rod n, 10 Gnt-1
2r
1
0
1 Z
C M
Fig. 3. Change in the gradient
of the index of refraction with
respect to the radius of the cell
(r is distance from the pumping
source): YI--30 mm Hg C3F7I +
440 mm Hg SF6; Y2--22 mm Hg C3F7I
+370 rvn H SF � Y--3 7 mm H
if a plane wave is sent to the input of the
first amplifier, the divergence at the output
of the third amplifier due to the found values
of the gradient of the refractive index should
not exceed 8E/2 a 0.5�10'4 radian.
3. Cptical decoupling mechanisms and radiation
contrast
One of the problems in developing facilities
for laser-driven nuclear fusion is attainment
of high radiation contrast* (107-108). For
this purpose, multistage amplification systems
use special means that forestall self-excitation
of the amplif iers, and specifically such optical
decoupling devices as Pockels cells, Kerr cells
and phototropic dqes. Here an examination will
be made of inethods that we have suggeste3 and
studied [Ref. 8, 20, 21, 29].
8 69 3 � g To ensure adequate contrast at the output of
C3F7I+ 150 mm Hg C02 + 440 mm Hg Ar the entire system, we must consider the fact
that the weak-signal gain in each amplifier is of the order of 102, while the
strong-signal gain (see relation (1)) is about 10-15. This means that the radia-
tion contrast in each stage will deteriorate by a factor of about 10, and the role
of interstage decoupling is not only to compensate far deterioration of the con-
trast, but to improve it. The careful selection of the parameters of the individu-
al amplifiers should serve this same purpose.
A very important parameter of interstage decoupling that determines the feasibility
of application of a given mechanism in a given design for preventing self-excitation
of the amplif iers and increasing radiation contrast is the ratio of transmission of
the main radiation pulse Tstrong to transmission uf Lhe weak signal (background)
Km Tstrong/Tweak� Since Tstrong determines the losses in the decoupling mechanism,
the ratio must be close to 100%.
To solve this problem, the authors of Ref.
iodine shutter. This device is a saturabli
transition 2P%-y 2P1/2 :�f the iodine atom.
8, 20, 39] that the weak-signal absorption
whereas monopulse transmission is -80X for
8, 20 proposed and developed a passive
~ absorb er that operates on the resonant
It has been experimentally shown jRef.
factor in such a shutter reaches 103,
a suff iciently intense incident signal.
The intensity dependence of transmission experimentally found [Ref. 20] for iodine
- laser emission with pulse duration ro 5�10-6 s throuih the shutter at T= 1050�C
with concentration of atomic iodine of ~3.5�1017 cm and molecular iodine concen-
iration of -1017 cM-3 is given in Fig. 4a together with the theoretical dependence
I/Ip = f(Ip) found at a molecular iodine quenching constant of 1.8�10'11 cm3 3-1,
For effective laser operation it is necessary that the width of the absorption line
*Radiation contrast is defined as the ratio of the energy of radiation in a
monopulse to the energy incident on the target before arrival of thz pulse.
7
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I/I
08
06
04
02
1
d v, 10"Z cM' ~
8
6
4
Z
don
0
P , mm Hg
Fig. 4. a--Transmission of the iodine shutter as a function of intensity (T=1050�C;
N1= 3.5�1017 cm 3). Points and solid curve experiment, broken line theory.
b--Absorption linewidth as a function of pressure in the cell (Av/Ap z 104 cm�torr-1)
(points show experimental data).
be close to that of the amplification line. When this is so, the absorption cross
section is somewhat larger than the amplification cross section.
Results of investigations of the way that absorption linewidth depends on the total
pressure in the cell are shown in Fig. 4b, from which we can see that as pressure
increases beginning at about 300 mm Hg, the absorption linewidth increases in pro-
portion to pressure with a widening constant of Av/t1p =10-`' cm�torr'1. Knowing
this dependence, we are able to choose the optimum parameters of the iodine shutter.
However, there are serious d ifficulties involved in developing an iodiae shutter
with aperture greater than 100 mm that is capable of transmitting energy measured
in the hundreds of joules. Therefore, we investigated the feasibility of using an
optical decoupl ing mechanism based on thin metal coatings sputtered on glass sub-
strates [Ref. 291* that become transparent to light under the action of laser radia-
tion due to the low degree of ionization of inetal during vaporization.
Analysis of the thermophysical and optical properties of a number of inetals has
shown that bismuth meets the necessary requirements. Table 1 gives the results of
an experimental study of the reduction in opacity of thin bismuth films with weak
signal passage of from 0.15 to lOX.
For a film with Tweak' 1%, strong signal transmission ranged from to 75% with a
change in the incident energy density from 0.7 to 2.1 J/cm2 (Fig.
Variation of Tweak by two orders of magnitude (see Table 1) leads to a relatively
small change in Tstron Possibly two coatings may be best, each of which passes a
= weak signal with Tweakg 10�G (ETweak - 1%, Tstrong � 80-902).
*Such films had been used previously [Ref. 40] to shorten pulse duration.
8
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200 400 600 800
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TASLE 1
Tweak+ x einc. J/cm2 IF-trans, J/cm2 Tstrongr y* K
0.15 1.7 0.88 52 345
- 0.25 1.9 1.22 63 250
1 1.5 1.13 70 70
2 1.5 1.2 80 40
5 1.26 1.1 87 17 -
10 0.26-0.4 0.23-0.38 90-95 9
- 2�10 0.26-0.4 0.12-0.36 80-90 80
*Tstrong - etrans/einc .
Tstrongt % Fxperimental values of K= Tstrong/Tweak
(Table 1) practically cover the working _
so o range of weak-signal gains of iodine amp-
_ so( cb o lifiers (50-500), which enables us to
~ choose a monopulse amplification mode
without deterioration of the radiation
contrast obtained at the output of the
einc+ J/cm2 master laser, and to prevent self-excita-
Fig. 5. Transmission of thin bismuth tion of adjacent amplification stages.
coatin s(T l~) Such shutters with diameter of about 50 cm
8 weak rs can handle laser beams with energy of a few
kJ with fairly Zow losses of energy to
reduction of opacity (-10-20X) and fairly high attenuation of the background signal
(by a factor of the order of 102 or more). This method can also be used to prevent
self-excitation of an amplif ier due to reflection of emission from the target.
Here it is sufficient to use a coating with TWeak = lOX to reduce the parasitic
coefficient of reflection from the target by a factor of 100 with a double pass _
through the coating.
We also investigated the feasibility of using nonlinear phenomena like stimulated
Mandelstam-Brillouin scattering (SMBS)* for interstage decoupling and obtaining
hlgh cuntrast [Ref. 21, 23, 281. This possib ility is determined by the threshold
naCure of onset of stimulated scattering. One arrangement for improving contrast
and cutting off the preliminary pulse that may arise in the master Iaser is shown
in Fig. 6.
For iodine lasers w ith a narrow luminescence band Av = 0.1 cm71 [Ref. 441, heavy
- compressed gases with a slow speed of sound (Xe, SF6) can serve as a working fluid
for SMBS; however, such med ia have a long relaxation time. As a result, the mode
of excitation of SMBS becomes very unsteady.
*At present considerable attention is being given to the possibility of using
the phenomenon of wavefront reversal [Ref. 41] for compensation of optical inhomo-
geneities [Ref. 42] and for guiding radiation to the targets [Ref. 28, 43] in laser-
driven fusion facilities. 9
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SMBS
�
RSMBS, x
80
60
40
ZO
0
13
J S 7 9 11
Epump/Ethr
Fig. 6. a--Experimental setup; b--reflectivity of SMBS mirror as a function of
excess over the threshold (Ethr =2�5 J/cm2). Points experiment; curve calcu-
lation
The possibility of getCing any high values of the coefficients of reflection from
SMBS mirrors (RSMgg) under these conditions seemed problematic and required experi-
mental studies, the results of which are shown in Fig. 6 in the form of a curve for
RgMgg as a function af excess of the pumping energy (Epump) over the threshold
_ energy (Ethr) � The maximum coefficient of reflection RgMgg = 70%. A numerical
study of the energy characteristics of the Stokes pulse in the case of SMBS for
, unsteady interaction as done in Ref. 23 in the plane-wave approximation showed good
agreement with the experiment (curve on Fig. 6).
TABLE 2
Radiation contrast (calculation for F.Pump/Ethr - 4)
Preceding the SMBS mirror After the SMBS mirror
(pumping) (Stokes line)
4 2�106
16 2�108
64 5�109
Experiments [Ref. 21] (Fig. 7a, b) and calculations (Fig. 7c) have shown that the
SMBS mirror eliminates the forerunner and considerably improves the enerly contrast.
The experimental data show that the attained contrast is greater than 10 (the
threshold of resolution of our methods at present), while the results of calcula-
tions summarized in Table 2 imply that the radiation contrast can b e increased to
108-109.
10
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I~
II il
a
I I j ~
I ~
I I {
~r3 . f ~ 1 j lmw
.~~'s ~
. i
t
; - . ~Fig. 7. Forerunner elimination and radiation pulse sharpening for iodine laser
with SMBS. Broken curves pumping, solid curves Stokes radiation; a, b--
experiment; c calculation
11
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4. MeChods of shortening laser pulse duration
Theoretical estimates and cumulative experience (see for example Ref. 45) show that
at energies of 4103 J incident on the target the pulse duration should not exceed
0.1-0.3 ns. In r'iis connection, let us call attention to the fact that when laser
emission intera::ts with the SIrBS mirror (see Fig. 7) there is considerable sharpen-
ing of the leading edge of the laser pulse and shortening of its duration. For
example in the experiment of Fig. 7b the rise time was shortened from -1 to -0.2 ns
(w1Ch consideration of the resolution of the instrumentation), and pulse duration
was shortened from -5 to -1 ns.
Calculations done for conditions close to the experimental conditions have also
shown that in the process of stimulated Mandelstam-Brillouin scattering the pulse
duration is shortened (Tg< TL) and the leading edge Tle is sharpened (see Fig. 7c).
The steepness of the leading edge depends appreciably on the excess of pumping
energy over the threshold value (zle = 1 ns at Ep/Eth = 1.4, and Tle = 0.2 ns at
Ep/Eth -14).
1 omN. ed re1:_ risits. -
72
8
4
0
1,5 3,D 4,5 6,0 ru,HC~
~ter F. M6
ma/"
laser E- Is ' SMBS
Le,7plasma
b shutter
~ 18bi2a `Olit �
Fig. B. Shortening the duration of iodine laser pulse radiation by stimulated
Mandelstam-Brillouin scattering and a plasma shutter; a--calculation; b--experi-
mental setup; c--experimental results
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The profiles of pumping and Stokes-line emission shown in Fig. 8 correspond to
F.p/Eth = 4. It can be seen that the leading edge is shortened by nearly an order of
magnitude, while the remainder of the profile practically repeats the shape of the
- stimulating radiatidn pul.se.
On the basis of the results, a master laser was developed for producing pulses with
_ controllable duration by using a plasma shutter to cut aff the trailing edge [Ref.
- 461 in the setup deacribed above with SMBS mirror. As a result, the shaped radia-
tion pulse had a duration (with consideration of the resolution of the equipment)
of -350-500 ps with energy up to 0.1 J(see Fig. 8). Shortening of laser pulse
duration with a steep leading edge may also be done during propagation in the ampli-
fic:ation stages operating under conditions of sufficiently strong saturation.
I, rel, units
075
0,50
025 ~
~
~
0 -
t, ns
Fig. 9. Shortening of duration of Stokes pulse during amplif ication (TP = 3 ns,
Ts = 1.1 ns, Tyl = 0.5 ns, Ty4 = 0.3 ns)
Calculations of the type of Ref. 23 showed (see Fig. 9) that a laser pulse having
half-amplitude duration tL = 3 ns and shortened by stimulated Mandelstam-Brillouin
scattering to zg = 1.1 ns is further shortened to 0.3 ns in the amplification pro-
cess. To shorten the duration of the iodine laser pulse to r a 10-10 s one can use -
the method of attenuation of free polarization (free induction) proposed in Ref. 47
and realized for the iodine laser in Ref. 46.
- In our experiments, which were analogous to those of Ref. 46, radiation with dura-
tion of -2.5 ns and energy of 0.4 J was sent from a master laser (ML) with pre-
amplifier (Fig. 10a) to a plasma shutter. From there a pulse with steep trailing
edge formed as a result of optical breakdown (Fig. lOb) was sent to an iodine
shutter [Ref. 8, 20] that cut off the flat leading edge (Fig. lOc). Z'he result was
a pulse with duration at half-amplitude of about 3�10-10 s. Analysis of the re-
sults with consideration of the time resolution of the equipment enabled evaluation
of the upper limit of duration of the pulse leaving the iodine shutter, which was
120 ps*. Qutput energy was 1-3 mJ at an input energq of 10-I5 mJ.
*In this connection it should be borne in mind that the minimum pulse duration
limited by bandwidth in an iodine laser is -40-100 us�atm [Ref. 17, 48].
13
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t.
6
9
:
b
c
t
t
- (1)TJfru~lHC , {2}tnn3el,3HC : . _ E3~,l3 = 4J1lC
. Master 13f /lnaan~ � Irtn ~ o e li
~r . I iam.B. samB.
laser 1~ shutter ~1 _ shutter
Fig. 10. Use of plasma and iodine shutters to shorten the duration of the emission
pulse of an iodine laser
KEY: 1--TMLa 2.5 ns
2--Tpl. sh.'w 1. 3 ns
3--Tiod. sh. m 0.3 ns
I, rel. units
Mq, SMBS
3r BPM6
~ JlBx= Iin
~ Q
o K odine Ibx~ Iin
G,7S hutter
I ee,z i p
Iout
/ -
'050 ut
/ .
. ~
025
/
/
/ , .
t - t'` I
p - Z 4 6
t, ns
Fig. 11. Shortening the duration of the Stokes-line pulse in an iodine laser:
a--equipment; b--calculation: Tp = 3 ns; Tin = 1 ns; Tout = 0.25 ns
14
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Combining the SMBS mirror with the iodine shutter (Fig. lla) gives an interesting -
possibilityfor shaping a laser pulse of short duration. To do this, the pulse
reflected by the SMBS mirror wiCh steep leading edge must be sent to a passive _
ehutter with narrow absorption line that passes the leading edge of the pulse and
_ filters out its flat trailing edge. This possibility has been checked and verified
by calculation (Fig. llb). It should be noted that the cor.trast may be very high
in the propos ed me thod .
5. The Iskra-IV high-power iodine laser.
The high-power iodine laser that we are develoFing consists of a master laser and
four amplifiers of increasing diameter and length. The master laser, which pro-
duces a pulae with the required duration and contrast, consists of the laser proper
with active Q-switching, two preamplifiers pumped by hollow lamps, and four Kerr
cells: a modulating cell, a cutof f cell and two decoupling cells.
The relatively weak input signal arriving from the master laser is preamplified in
the first two amplifiers Y1 and Y2 in which the working medium to be pumped by the
- lamps is contained in quartz cell s. Amplifiers Yg and Y4 are intended for getting
the maximum output energy in the monopulse mode, and in this connection they have
relatively large overall dimensions. This makes it possible to get high output
energy in a single beam, which in turn optimizes both the number of stages and
the number of beams for irradiating a target at a given energy.
Repeat-action electrodischarge sources [Ref. 15] are used for circulating the large
- croes sections of active medium in these amplifiers. Amplifiers Y3 and Y4 consist
of two or more sections. Around each section, on a circle with diameter of about
- 40 cm, are 9 sources each 2 m long. An electric energy of 65 and 85 kJ (in Y3 and
Yy respectively) is sent to each source from a specially developed capacitive accu-
mulator with stored energy of abou t 4 MJ. Its characteristics make this accumu-
latar one of a kind: with voltage of 50 kV and energy capacity of about 4 MJ the
duration of the discharge half-period is less than 40 ug� And experiments have
shown that about 70% of the electric energy stored in the accumulator is released
in the first half-peiod. The perfluoroalkyl iodide p-C3F7I mixed with various
buffer gases (C02, SF6, Ar) was taken as the working substance for all stages.
The pressure of the components of the working mixture was chosen in such a way that
the weak-signal gain did not exceed 100. To prevent self-excitation and improve
the spatial structure of the beam, decoupling mechanisms P1 and P2 were connected
at the output of amplifiers Y1 and Y2. These decouplers were passive shutters com-
bined with apatial selectors. Pho totropic bismuth coatings are now used as the -
passive shutters. -
Without going into detail as to the results of the experimental study of the master
laser and each of the amplifiers individually, we give the results of experiments
in which the operation of the laser as a whole was studied in the monopulse mode `
(Table 3).
We can see from the table that re sults close to those anticipated were realized
even in the f irst experiments. The radiation energy obtained at the output of the
final stage is greater than that produced in a single beam on any other tyge of
laser at T z 10-9 s. The efficiency of u,"ilization of the accumulator energy is
0.1%. Beam d ivergence on the 80% energy level was 3�10-4 radian. Radiation energy
-.ontrast exceeded 106.
15
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T: BLE 3 _
Version 1 Version 2
Sta e il x Za, Og~ pC3F7I K0 ~ou* ilcmla~ IPC8F7I KO E J* ~
cm
ML 1.6X80 50 1000 0.5 1.6X80 50 1000 0.5
_ Y1 3.6X100 30 300 6 3.6X100 30 360 5
(7)
Y2 8X200 22 77 33 8X200 22 140 30
(30) (30)
Y3 40X400 4.5 90 360 40x400 4.5 100 300
(390 (320)
y4 - - - - I 50X400 4.5 125 (11400
600)
The results given here show that many capabilities of iodine lasers have been suc-
cessfully realized. However, there are still many problems waiting to be'solved:
_ Increasing contrast to 107-108, shortening pulse duration to 0.1-0.3 ns, raising
laser efficiency to 0.3-0.5%, reducing beam divergence to -10'4 radian, improving
the spatial structure of the beam, developing optically stable reflective and photo-
tropic coatings for the optical elements of amplifiers and the reprojecting optics.
Cumulative experience and the results of research done both in the Soviet Union and
elsewhere indicate that these problems can be solved, which makes the iodine l.aser
a useful tool for studying the crucial problems of laser-driven fusion.
REFERF.NCES
1. S. G. Rautian, V. I. Sobel'man, ZHURNAL EKSPERIMENTAL'NOY I TFARETICHESKOY
FIZIKI, Vol 41, 1961, p 2018.
2. J. V. Kasper, G. C. Pimental, APPL. PHYS. LETTS, Vol 5, 1964, p 231.
3. T. L. Andreyeva, V. A. Dudkin, V. I. M~.lyshev et al., ZHURNAL EKSPERIMENTAL'NOY
I TEORETICHESKOY FIZIKI, Vol 49, 1965, p 1408.
- 4. A. J. De Maria, C. J. Ultee, APPL. PHYS. I,ETTS, Vol 9, 1965, p 67.
5. C. M. Perar, APPL. PHYS. LETTS, Vol 12, 1968, p 381.
6. P. Gensel, K. Hohla, K. L. Kompa, APPL. PHYS. LETTS, Vol 18, 1971, p 48.
7. N. G. Basov, L. Ye. Golubev, V. S. Zuyev et al., KVANTOVAYA II.EKTRONIKA, No 6
(18), 1973, p 116.
8. V. A. Gaydysh, G. A. Kirillov, S. B. Kormer et al., PIS'MA V ZHURNAL EKSPERI-
MENTAL'NOY I TEORETICHESKOY FIZIKI, Vol 20, 1974, p 243.
9. F. I. Alridge, APPL. PHYS. LETTS, Vol 22, 1973, p 180.
16
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10. R. E. Palmer, H. A. Gusinow, IEEE J. QUANT. II.ECTRON., QE-10, 1974, p 615.
11. H. J. Baker, T. A. King, J. PHYS. D, Vol 8, 1975, p 131.
12. G. Brederlow, K. I. Witte, E. Fill et al., IEEE J. QUANT. ELECTRON., QE-12,
1976, p 152.
,
13. LASER FOC[iS, Vol 2, 1976, p 4.
14. N. G. Basov, V. S. Zuev, V. A. Katulin et al., "Laser und ihre Arnaendungen,"
Dresden, 1977, p 52.
15. A. V. Belotserkoveta, V. A. Gaydash, G. A. Kirillov et al., PIS'MA V ZHURI3AL
TEKHNICH ESKOY FIZIKI, Vol 5, 1979, p 204.
16. K. Hohla, G. Brederlow, E. Fill et al., Max-Planck Institut fur Plasma Physik,
IPP IV/93, 1976.
17. W. Fuas, K. Z. Hohla, NATURFORSCH., Vol 31a, 1976, p 569; W. Fuss, K. Hohla,
Institut fur Plasma Physik, Report IPP IV/67, Garching, Germany, 1974.
18. K. Hohla, "Laser-75 Opt-Electron. Conf. Proc.," Munich, 1975, Guildford, 1976,
p 52.
19. J. Willson, D. 0. Ham, LASER FOCUS, Vol 12, Ido 11, 1976, p 38.
20. V. A. Gaydash, V. A. Yeroshenko, S. G. Lapin et al., KVANTOVAYA ELEKTRONIKA,
Vol 3, 1976, p 1701.
21. S. B. Kormer, S. M. Kulikov, V. D. Nikolayev et al., PIS'MA V ZHURNAL TEKHNI-
CHESKOY FIZIKI, Vol 5, 1979,'p 213.
22. L. I. Zykov, G. A. Kirillov, S. B. Kormer et al., KVANTOVAYA ELEKTRONIKA, Vol 4,
Nn 6, 1977, p 1336.
23. Yu. V. Dolgopolov, Yu. F. Kir'yanov, S. B. Kormer et al., in: "Obrashcheniye
volnovogo fronta opticheskogo izlucheniya v nelineynykh sredakh" [Wavefront
Reversal of Optical Radiation in Nonlinear Media], Institute of Applied Physics
of the USSR Academy of Sciences, 1979.
24. L. I. Zykov, G. A. Kirillov, S. B. Kormer et al., ZHURtJAL EKSPERIMENTAL'NOY I
TEORETICHESKOY FIZIKI, Vol 67, No 3(9), 1974, p 902.
25. A. I. Zaretskiy, G. A. Kirillov, S. B. IGormer, S. A. Sukharev, KVANTOVAYA ELEK-
TRONIKA, Vol 1, 1974, p 1185.
26. G. A. Kirillov, S. B. Kormer, G. G. Kochemasov et al., KVANTOVAYA ELEKTRONIKA,
Vol 2, 1975, p 666.
_ 27. L. I. Zykov, G. A. Kirillov, S. B. Kormer et al., KVANTOVAYA ELEKTRONIKA, Vol 2,
_ 1975, p 123.
17
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28. Yu. V. Dolgopolov, V. A. Komarevskiy, S. B. Kormer et al., ZHURNAL EKSPERIMEN-
TAL'NOY I TEORETICHESKiDY FIZIKI, Vol 76, 1979, p 908.
29. S. B. Kormer, V. D. Nikolayev, N. N. Rukavishnikov, S. A. Sukharev, PIS'MA V
ZHURNAL TEKHNICHESKOY FIZIKI, Vol 5, 1979, p 1416.
30. J. Vevges, SPECTROCHIMICA ACTA, Vol 24B, No 3, 1979, p 177; I. M. Belousova,
V. M. Kiselev, V. N. Kurzenkov, OPTIKA I SPEKTROSKOPIYA, Vol 33, 1972, p 203;
V. S. Zuyev, V. A. Katulin, V. Yu. Nosach, 0. Yu. Nosach, ZHURNAL EKSPERIMEN-
TAL'IvOY I TEORETICHESKOY FIZIKI, Vol 62, 1972, p 1673.
_ 31. V. A. Alekseyev, T. L. Andreyeva, V. N. Volkov, Ye. A. Yukov, ZHURNAL EKSPERI-
MENTAL'NOY I TEORETICHESKOY FIZIKI, Vol 63, 1972, p 453; Ye. A. Yukov, KVANTO-
VAYA II.EKTRONIKA, Vol 3, 1973, p 117.
32. L. M. Frantz, J. S. Nodvik, J. APPL. PHYS., Vol 34, 1973, p 2346; P. V. Avizonis,
R. L. Grotbeck, J. APPL. PHYS., Vol 37, 1966, p 687.
- 33. S. M. Andreyev, S. G. Baykov, P. N. Dashuk et al., OPTIKO-MEKHANICHESKAYA PRO-
MYSHLENNOST', No 5, 1972, p 19.
34. A. S. Antonov, I. M. Belousova, V. A. Gerasimov et al., PIS'MA V ZHURNAL TEKH-
NICHESKOY FIZIKI, Vol 4, 1978, p 1143.
35. B. V. Alekhin, B. V. Lazhinttczv, V. A. Nor-Averyan et al., KVANTOVAYA'ELEK-
TRONIKA, Vol 3, 1976, p 2369.
- 36. A. V. Zaretskiy, L. I. Zykov, G. A. Kirillov et al., KVANTOVAYA ELEKTRONIKA,
Vol 6, 1979, p 1278.
37. N. G. Basov, V. S. Zuyev, V. A. Katulin et al., KVANTOVAYA ELEKTRONIKA, Vol 6,
No 2, 1979, p 311.
38. I. M. Belousova, 0. B. Danilov, I. A. Sinitsyn, V. V. Spiridonov, ZHURNAL EKS-
PERIMENTAL'NOY I TEORETICHESKOY FIZIKI, Vol 58, 1970, p 1481.
39. E. Fill, K. Hohla, OPT. COMMUNS., Vol 18, 1976, p 431.
40. M. P. Vanyukov, V. I. Isayenko, P. P. Pashinin et al., KVANTOVAYA ELEKTRONIKA,
No 1, 1971, p 35.
41. B. Ya. Zel'dovich, V. I. Popovichev, V. V. Ragul'skiy, F. S. Fayzullov, PiS'MA
V ZHURNAL EKSPERIMENTAL'NOY I TEORETICHESKOY FIZIKI, Vol 15, 1972, p 160.
42. 0. Yu. Hosach, V. I. Popovichev, V. V. Ragul'skiy, F. S. Fayzullov, PIS'MA V
ZHURNAL EKSPERIMENTAL'NOY I TEORETICIIiSKOY FIZIKI, Vol 16, 1972, p 617.
43. Yu. I. Kruzhilin, KVANTOVAYA ELEKTRONIKA, Vol 5, 1978, p 625.
44. V. S. Zuyev, V. A. Katulin, V. Yu. Nosach, 0. Yu. Nosach, ZIiURNAL EKESPERIMEN-
TAL'NOY I TEORETICHESKOY FIZIKI, Vol 62, 1972, p 1673.
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45. J. A. Maniscalco, Lawrence Livermore Laboratory, Report UCRL-76763, Livermore,
California, 1975; Lawrence Livermore Laboratory, Laser Program Annual Report,
1976, UCRL-50021-7 6, Livermore, Calif., 1977; Lawrence Livermore Laboratory,
Laser Program Annual Report, 1977, v. 1, 2, UCRL-50021-77, Livermore, Calif.,
July, 197ti.
46. E. Fill, K. Hohla, G. T. Schappert, R. Volk, APPL. PHYS. LETTS, Vol 29, 1976,
p 805.
47. E. Yablonovitch, I. Goldhaar, APPL. PHYS. LETTS, Vol 25, 1974, p 580.
- 48. E. P. Jones, M. A. Palmer, F. R. Franklin, OPT. QUANT. ELECTRON., No 8, 1976,
_ p 231.
COPYRIGHT: Izdatel'stvo "Nauka", "Izvestiya AN SSSR. Seriya fizicheskaya", 1980
[8144/0285-6610]
6610
CSO: 8144/0285
A
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UDC 678.7.352
CHEMICAL LASERS: NEW RESULTS AND IDEAS
Moscow IZVESTIYA AKADEMII NAUK SSSR: SERIYA FIZICHESKAYA in Russian Vol 44, No 8,
Aug 80 pp 1554-1565 -
[Article by A. N. Orayevskiy, Physics Institute imeni P. N. Lebedev, USSR Academy
of Sciences]
[Text] This article is based on results and ideas arrived at and elaborated in the
Lebedev Physics Institute. Results found in other laboratories will be mentioned
only inasmuch as they are pertinent to our research. Many details of design and
principles of operation of chemical lasers are omitted. This type of information
is now readily accessible in a number of books that have already been published
[Ref. 1-3]*.
Chemical cw lasers
Fig. 1 shows a achematic diagram of a cw chemical laser that has now become conven-
tional for lasers based on reaction of atomic fluorine with hydrogen:
F +H2 -+HF*+H.
Major parameters that have been realized up to this point in a number of labora-
tories are summarized in Table 1.
Fig. 2 shows a diagram of a purely chemical DF-C02 laser utilizing initiation of a
chain reaction in a mixture of D2 + F2 by the NO radical. Such a laser has been
studied by many authors at subsonic discharge of reagents. Laser parameters are
summarized in Table 2.
Supersonic versions of the DF-C02 laser are also known, both with gas generator
initiation [Ref. 2, 3] and with initiation by the NO radical [Ref. 41 (Table 3).
The latter is of interest because of its high pressure (233 mm Hg), although it has
lower chemical efficiency (-1.9X) than the subsonic version (4-5x).
= Many questions arise in connection with the utilization of lasers of this type.
Among these questions are the fo llowing. Can the specific energy output be in-
creased, or have limiting parameters already been attained? Can the pressure in
*Ref. 2 was translated into Russiaa this year [Mir publishers, Moscow, 1980).
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,
the cavity be increased without impairing the laser characteristics? Can another
system be found that is energetically comparable with the HF laser but with non-
toxic reaction products? This part of our article will be devoted to development
of a number of ideas that give an affirmative answer to these questions.
TABL E 1
HF laser
1. Specific energy e 150-200 J�g-1
2. Static pressure p in the S mm Hg
laser cavity
3. Flow velocity v
4. Typical molecular compo-
sition of the mixture
[F]:[H2]:[He] in the
laser cavity
2�105 cm�s-1
1:9:10
TABLE 2
DF-C02 laser
1. Specif ic energy e 50-60 J�g-1
2. Static pressure p in the 15 mm Hg
laser cavity
3. Flow velocity v
4. Initiating process
5. Molar composition of the
mixture [F2]:[D2]:[C02):[He]
in the laser cavity
Total power P
- Flow of reagents
F2
COZ
D2
He
NO
Pressure p in laser cavity
Temperature in initiation
chamber
Chemical efficiency
Mach number M at nozzle tip
2�104 cm�s'1
NO+F2->F+NOF
1:1:8:15
TABLE 3
1 1.45 kW
5.29 g s-1
57.8 g s-1
1.61 g s-1
15.1 g s-1
1.53 g s-1
233 mm Hg
300 K
1.9%
1.5
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(2).
� H;: -__.~-_~--.r ~ _
/ ~ � . . ~ ~ � ` ~ ~ f
(3
~ . r; J J '
(4~ (2}t
Fig. 1
Fig. 2
. Fig. 1. Schematic diagram of a cw chemical HF laser
Fig. 2. Schematic diagram of a cw chemical DF-C02 laser
KEY: 1--Nozzle
2--Mirror
3--Laser cavity
4--Combustion chamber
S--Evacuatian
The main reserve for increasing the specific energy (power) of a cw laser is in the
use of a chain reaction of hyclrogen with fluorine. The reaction between hydrogen
, and fluorine develops in a chain mechanism �
F+H2 +HF*+H (32 kcal mol'"1 HF), (2)
H+ F2 +HF* + F(98 kcal mol-1 HF).
We noted previously that the development of chemical lasers has taken the path of
utilization of the former of these reactions. But if the second stage of this re-
action is used, by adding a sufficient amount of molecular fluorine to the mixture,
the average energy per HF molecule increases to 65 kcal mol-1. It turns out that
converting to the chain-reaction mode promises to more than double the specific
power charactzristics of the laser. If consideration is also taken of the fact
[hat the initial amount of atomic fluorine has to be less for the chain-reaction
process, then the specific power output should be even more appreciable [Ref. 5, 6].
A"savings" is possible on this basis. The fewer the atoms of fluorine, the less
the "fuel" expended on creating them, the less the reaction products that deacti-
vate the active molecules in the laser cavity. The fewer the atoms of f luorine,
the more slowly the reaction develops, and the better the mixing process can be
organized.
Shown in Fig. 3 are the results of calculation of che behavior of gain in the
chain-reaction HF laser along the flow of the jet [Ref. 6]. It can be seen that
at low initial fluorine concentrations the reaction is noticeably delayed, which
increases the time reserve for more effective intermixing of the jets. Such argu-
ments in favor of chain-reaction lasers prompt the question: why haven't they
already come into use, the moreso as chemical lasers have been successfully using
the advantages of the chain-reaction process for a long time now? The answer to
22
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~ tr w
(2)
lie~
~
. /
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this question is that development of a cw chemical laser based on a chain reac:ion
requires overcoming a number of difficvlties, the most fiindamental being the heat
crisis of supersonic f low. In this phenomenon, as heat is released in a supersonic
jet of constant cross section it loses velocity, and the supersonic flow may be
interrupted, accompan ied by an abrupt rise in temperature in the jeC, which in tne
final analysis leads to interruption of lasing.
dn' ,�rm, -:ri (rel.
C
r. , 'i
ni.ts) r :
4 ~
I .
IU ~ 0 , .
CM ~
Fig. 3
Fig. 4.
Fig. 3. Downstream development of inverse population AN for chain-reaction :iF
laser. The distance f rom the nozzle tip is laid off along the axis of abscissas.
Fig. 4. Temperature of the jet of reacting flow in HF laser with cylindrical
nozzle array as a function of distance from the nozzle array (chain reaction)
A helium diluent is used in the cw chemical laser to eliminate the flow heat crisis.
- But when the chain reaction is used, the heat release in the laser zone rises
_ sharply, and the problem of the flow heat crisis becomes much more complicated.
llilution of the flow would lead to an increase in helium expenditure and a reduc-
tion of specific power output. Another method, separation of jets, severly in-
_ creases the dimensions of the system.
The most effective way out of this difficulty is to use a cylindrical configuration
in the nozzle array. At the Lebedev Physies Institute, detailed calculations have
been done on a cw HF laser with initiation by a nozzle array [Ref. 7]. Equations
of gasdynamics and of the usual kinetics of a chemical laser were simultaneously
s4lved in this research. In doing this, consideration was taken of flux, diffus ion,
viscosity and thermal conductivity of the jets. The equations used in Ref. 7 wer e
written in the boundary layer approximation. The justification for this approach
ls the small transverse dimension of the intermixing jets. The most interesting
results of the work are discussed below.
Shown in Fig. 4 is the behavior of the jet temperature along the flow as a function
of the radius rp of the cylindrical nozzle array. An abrupt rise in flow tempera-
ture in the case of a f lat nozzle array (rp = 105 cm) begins almost immediately
beyond the tip of the nozzle units, whereas for a radius rp=20 cm the temperature
is retained up to distances r- rp = 10-12 cm which are of practical interest. The
temperature rise in the vicinity of 12-15 cm at rp = 20 cm is not as abrupt and
_ catastrophic as for a f lat nozzle assembly. Let us note that the emission, in
coupling out part of the energy of the flow, helps to eliminate the flow crisis.
- Calculations show that at SHe =[He]/[F2'j = 10 and rp > 10 cm in the absence of lasing
23
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a flow criais sets in, whereas there is nc such crisis in the lasing mode even when
rp - 20 cm, as can be seen from Fig. 4. Emission has a considerable effect on gas
dynamics. ,
,
d r'
I, kW�cm-2 ls
~ Cnt
40 10
i
O0 ZO 40 r,,cn+
- � Fig. 6
.i c11/

lV U
,l J ru . -1o, r.nr
Ep, kJ�g 1
I, 'L r J S
0 ZO 40 ro,t,N
Fig.. 5 Fig. 7
Fig. 5. Intensity distribution along the flow for radiation of an HF laser with
cylindrical nozzle assembly (chain reaction): a--radius rp of nozzle unit 30 cm;
b--radius of nozzle unit 15 cm. Pressure in the cavity 15 mm Hg; Bge=[He]/[F2]p=10;
[F2 1p is the initial concentration of fluorine molecules in the comb::stion chamber
(gas generator)
Fig. 6. Width of raciiation band of the HF laser as a function of the radius of a
cylindrical nozzle unit (chain reaction). The numbers near the curves show tte
valuea of Sge
Fig. 7. Specific radiation energy of HF laser as a function of the radius of the
cylindrical nozzle unit (chain reaction). Notation same as in Fig. 6.
' Fig. 5 shows the distribution of intensity of HF laser emission integrated over the
entire radiation spectrum. The intensity distribution along the flow that is char-
- acteristic of a chain reaction is retained in the cylindrical version as well. As
the radius increases, the distribution is compressed along the flow. This circum-
stance is reflected by Fig. 6, which shows how the width of the lasing band Arn
_ depends on rp.
Finally, Fig. 7 shows important results of calculation of the specific energy be-
havior of a laser with a cqlindrical cavity. Zt can be seen that for each degree
of dilution age there is an optimum radius of the nozzle unit for whiGh the spe-
cif ic power output is maximum. Calculation shows that the maximum specif ic power
output may reach considerable values of 800-1 000 J�g 1 at a pressure of p= 15 mm Hg
on the tip of the nozzle assembly. Thus using the chain reaction of hydrogen with
fluorine in combination with a cylindrical conf iguration of the nozzle array can
appreciably improve the characteristics of cw chemical lasers.
- The search for chemical lasing mixtures with nontoxic discharge has been to some
extent successful, with a good outlook for progress in solving this problem. The
following exposition will show what we mean by this statement.
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Joint research by the Lebedev Physics Institute and Moscow Engineering Physics
Institute on the OD-C02 laser, which was first discovered in Ref. 8 showed that
this laser has good potential capabilities [Ref. 9-12]. T?-'3 laser is pumped by
the procesa
D +Og -OD* +02,
OD* + C02 + OD + C02* . ~3~
The lasing molecule is C02. The end products of the reaction (02, C02, D20) are
nontoxic. The characteristics of suCh a laser were studied on the facility dia-
grammed in Fig. 8[Ref. 12]. Atomic hydrogen was produced in shock tube 1 behind
the wave front of the shock wave pronagating in the mixture of Ar + D2 after reflec-
tion f rom diaphragm 2. The hot mixture of Ar + D2 + D was discharged from the nozzles
of the cellular nozzle array and mixed with d stream containing C02 + Og + He. Dif=
f erent mixing arrangements were studied. Among the investigated designs, the best
results were obtained with the mixer diagrammed in Fig. 9 with parameters shown in
Table 4.
cily' 0. ' v~

- Fig. 8. Diagram of experimental OH(OD)-C02 laser: 1--shock tube; 2-- diaphragm;
3--electric valve for injection of mixture of 03 +C02 +He; 4--nozzle array; 5--
acCive lazer zone; 6--windows for coupling our laser emission
- R (5
R \ ;
V ~ a e � ~
A" .
0'� COZ+ Ne
Fig. 9. Design of the nozzle array of the OH(OD)-C02 laser: a--side view across
the flow; b--end view of the nozzle (orifices for injection of Og+CO2+He mixture
are displaced relative to one another in the upper and lower parts of the nozzle)
Thus Table 4 shows that the supersonic OD-C02 laser has a considerable specific
power output, a fairly extended lasing zone and high static pressure in the cavity.
At first glance, it seems to have a specif ic energy output about half the level of
the DF-C02 laser. However, in reality the specific energy of the OD-C02 laser can
be appreciably improved if Ar is elimir.zted from the mixture, as it is not essential
and is only there because of the method used for getting atomic deuterium. Wkien we
recalculate for helium, we get a specific energy of 60 J�g-1, which is on the level
of this parameter for the DF-C02 laser.
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Composition for the mixture
of 103+ 02]:[c021:[xe]
Gain K
Specific energy E
Pressure p in laser cavity
Flow velocity v
Width of inversion zone
_ along the flow .
Lasing time T
Total lasing power P
Nozzle dimensions
hcr
hout
TABLE 4
1:12:30
2.65 � 0.13 m 1
35 J�g'1
15mmHg
1.8�105 cm�s'1
20 cm
I 2 ms
960 W
I 0.45 mm
2.7 cm
One of Che most interesting results of the studies done in Ref. 12 is the discovery
that substituting hydrogen for deuterium does not cause any appreciable fall-off in
laser characteristics. An experiment showed [Ref. 12] that the OH-CO2 laser has a
gain only 8�6 lower than that of the OD-C02 laser, and nearly the same specific
energy output. This is an important factor that increases interest in the OH-CO2
laser.
In order to give the proposed laser the appearance of a structurally finished system
it is necessary to learn how to produce atomic hydrogen by a chemical method. Our _
calculations showed that the required concentrations of hydrogen can be obtained by _
utilizing combuation of hydrogen in oxygen. All these factors show the promise of
research on developing a purely chemical OH-CO2 laser with nontoxic discharge
products.
- In discussing the recent advances in the field of cw chemical lasers, we must not
overlook the development of a purely chemical laser by U. S. researchers [Ref. 13,
141. The radiative transition in this laser is
I(1':.)--i(P,)4-~,.�. (4)
Atomic iodine in state P1/2 is obtained by transmission of a quantum of energy from
_ singlet oxygen
(5)
Since P3/2 is the ground state, inversion results from the excess of quantum 02(1A)
- over the quantum necessary for excitation of I(P1/2).
And finally, the most striking part of this arrangement is that atomic iodine is
obtained from molecular 12 due to the energy of singlet oxygen
'~(~;{'.\)-�-T.- :'!1.( 1
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Oxygen in srate 16 is produced by the well known reaction of chlorinating hydrogen
peroxide [Ref. 15]. It is difficult as yet to predict the future of this laser.
One thing is certain: its development involves a number of ideas that widen our
concepta in the field of kinetics.
Pulsed chemical lasera
One of the major advances in the field of pulsed chemical lasers over the last two
or three years is a deeper understanding of the processes that take place in the
- reactor and that influence the characteristics of the chemical laser. It was shown
in particular that rapid establishment of rotational equilibrium of the lasing mole-
cule ia conducive to an increase in the power output and efficiency of the lasers
(Ref. 16, 17]. The use of vibrational-rotational transitions with a large rota-
tional quantum number (J x 10-15) for lasing and amplification should increase the
power output and eff iciency under conditions of rotational equilibrium [Ref. 18].
At the same time, it has been shown that rotational equilibrium is not established
in HF molecules during the time of the lasing pulse in a laser medium of widely
uaed composition [Ref. 19-26], so that the problem arises of adding an effective
"relaxer" of rotational levels to the mixture. It was shown in Ref. 17 that the
addition of such a relaxer is.actually conducive to improvement of the efficiency
and energy output of the chemical laser. In some papers, theoretical models that
- account for the finite time of establishment of rotational equilibrium have been
developed on the basis of ineasured cross sections of rotational relaxation [Ref.
_ 17, 27, 28].
A more precise understanding on ihe part of experimenters concerning the particulars
of different methods of initiating chemical lasers has led to appreGiable improve-
_ ment of technical efficiency and power output. Table S summarizes results found at
the Lebedev Physics Institute in studying pulsed chemical lasers with various
methods of initiation.
TABLE 5
Mixture
~
Method of
initiation
nchemp
�6
nel~
X
T' S
p p
atm
EP
J/Z
E, J
Ref.
UV radiation of an
7
15
5�10-6
1
150
20
29
D2+F2+CO2+He
open creeping dis-
charge
Electron beam
3.5
330
4�10-6
1
60
7
30
W radiation of
3.5
25
4�10'6
1
25
125
31
flashlamps
H2+F2+He
Electron beam
5
960
10-6
1
100
13
32
Most of these results are record-breaking. Among non-Soviet studies, we can men-
- tion the following. Ref. 33 reported attainment of an efficiency of 370% in an
electronically initiated laser, but at a specific energy output of 50 J/Z. The
au[hors of Ref. 34 were able to noticeably improve the specific energy output by
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a sharp increase in the degree of initiation. Although the authors of Ref. 34 do
- nor cite this parameter, the experimental data indicate a specific energy output of
the order of 300-500 J/l. This result was attained at the cost of a reduction in
efficiency to 180%. Let us note in passing that the overall lasing energy of -
4.5 kJ attained in Ref. 34 is eo far the greatest value of this parameter published
for HF lasere.
Ref. 35 by U. S. researchers reported on attainment of an efficiency of about 30%
with respect to energy initiation in an HF laser at a specific energy output of
22 J/Z. From the standpoint of efficiency, this is the best figure published to
daCe. However, the results are not quite up to ours as regards specific energy
ouCput. There is room here for further progress, and there are reserves in more
improved sources of UV radiation. It may be possible to use the luminescence of
excimers excited by electron impact (electron beam, the electroionization method,
other types of discharges).
The results given in Table 5 show that electronic initiation is more effective for
- HF lasers than for DF-C02 lasers. The reason for this is in the comparatively
large absorption of electron energy by C02 molecules in the case of the DF-C02
laser, as this absorption in the best case is of no use for further development of
the process.
Despite the fact that an electron beam injects the initiating energy into the mix-
ture of reagents more economically than UV flashlamps, the latter sources are still
just as attractive to experimenters because of their simplicity and low cost as
compared with a source that produces a high-current electron beam. The efficiency _
with respect to the initiation energy introduced into the mixture is given in Table
5 for the case of electron-beam initiation. The actually realized efficiency ("from
the plug-in point") is about one-fourth of this. In the first place the efficiency
of tlie accelerator will scarcely exceed Sd%. Secondly, it is difficult to combine
initiation with 100% utilization of the beam in the laser reactor. With consider-
ation of input losses, the beam utilization factor is about 50%. The efficiency of
initiation by W radiation cited in Table 5 refers to the energy stored in the
capacitor bank.
Comparison of experiments with very intense initiation [Ref. 34] and with moderate
initiation (see Table 5) leads us, as it were, to the conclusion that there is an
alternative: either high efficiency with respect to investment of initiation
energy, or else high specific energy output. This conclusion also has its theo- _
retical basis: the principal deactivator of excited molecules in chemical lasers
is the reaction product molecules of HF (DF). However, the chemical laser is a
multiparameter system. And it turns out that by matching parameters we can find
operating conditions such that this alternative does not occur for all practical
purposes. It has been tr.eoretically established [Ref. 36] that in a high-pressure
DF-C02 lasers the composition of the mixture and degree of initiation can be matched
to achieve an increase in both the specific energy output and efficiency with re-
spect to the energy that initiates the reaction. The results of these calculations
are shown in Table 6.
The effect of increasing quantum yield of lasing with an increase in pressure of
the mixture as energy output increases takes place only at a sufficiently high
degree of initiation (4�1016 cm 3). At a lower degree of initiation (2�1015 cm-3)
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TABLE 6
~
. , 1,
a ot
e J/Z
, .l.r�.i-
~
I
T s

I
f
~i~
.
'

I,:S jU�n I
131. -
.
~
. i~
_
'i
7 ',U
I�1lI-~
l�lU-G
.S~S.i
: i I
S:i
'?�IU-~ ~
llf~~
.
,
i Gl

1.1�lu-'' ~
~
1 ~Gu
j
1�IU-~ :
9 12

No te: D2: F2: C02: He = 1: 3.8: 3: 4.8,
tp - 10-7 s, tp
is the time of
initiation of the
_ reaction, [F] is the concentration of active centers, T is lasi
ng pulse duration,
f is the quanCum yield of emitted
radiation per
fluorine atom
this is not observed (Table 6). I
t is a matter
for experiment
to verify the
validity of this prediction.
Redical solution of the problem of attaining high efficiency with respect to initi-
ation energy involves using branching processes.
It ia well known that from the chemical standpoint a reaction in a mixture of H2-F2
is a branchimg process [Ref. 37]. This means that during the reaction itself chemi-
cally active centers are accumulated with concentration that increases in accordance
with an exponential function [Ref. 37, 38]*
- ' [1'] ~[(7)
_ However, because of the low rate of branching s, the part played by this process
in development of lasing is small. Recently experiments were done [Ref. 39] that
ahowed that the rare of branching incre=Qes sharply if vibrstionally ExciLau hydro-
- gen with energy of two or more vibrational quanta participates in the branching
reaction.
- This brought us once more to the analysis of the possibilities of branching for
development of lasing in a chemical DF-COZ laser since during the reaction D(v > 2)
may arise through energy transfer from DF molecules (v > 2). It was found that such
possibilities exist. The reaction can be initiateii in two ways: 1) introducing a
ema 11 concentration of DF (HF) molecules into the mixture that are stimulated by
DF (HF) laser radiation and transfer their energy to molecules of D2 (HZ); 2) weak
initiation of the reaction by W photolysis, which leads to formation of a"start-
ing"number of DF molecules (v > 2). The results of the calculation are shown in
Tab le 7[Ref. 40]. The calculation shows that we can achieve satisfactory specifit:
energy outputs (-40 J�1'1 atm 1) with negligible expenditures of energy on initia-
tio n. Even if the efficiency of the lamp emission into the band of fluorine dis-
soc iation is of the order of 1%, the laser radiation energy will be dozens of times
greater than the total expenditures of energy on initiation of the reaction.
*The exponential law is valid only in the linear stage of the reaction.
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TABL E 7
IR-initiation
(DF molecules are added to the mixture; PDg�l mm Hg)
Initiation energy, J/Z 5.5 1.1 0.3
Lasing energy, J/Z 36 31 36.6
Pulse duration, s 4�10'4 9�10'4 1.6 �10-3
W-initiation
Number of fluorine atoms 3�1013 3�1012
per cm3
Initiation energy, J/Z 10-2 10-3
Lasing energy, J/Z 43 29
Pulse duration, s 1.2�10-4 3�10-4
~ One raight ask why this eff ect has not been experimentally observed. The fact is
that relaxation of vibrational energy of DF(v 2) and D2(v > 2) due to V-V exchange
with C02 molecules is an obstacle to development of the branching process. There-
fore mixCures are needed with relatively large ratio of [F2]/[C02] and [D2]/[C02],
and these are no t the optimum mixtures if lasing is due to a straight chain.
Another reason is that the branching process is very critical to the oxygen content
in the mixture: for a mixture of the given composition its content should not
exceed 0.3 mm Hg. Since oxygen is added to stabilize the mixture, stimulation of
emisaion by a branching process requires solution of the problem of preparing mix-
tures with a very small oxygen content.
The possibility of initiating chemical reactions by IR radiation has led to ad-
vancement and formulation of the idea [Ref. 41] of photonic branching of a chemical
process: if the number af emitted photons in the process of the reaction that
accompanies IR radiation is greater than the number of photons required for initi-
ation, the reaction will be a branching process. If in addition the process of
emission may be stimulated, then by using a resonator to control emission we can
in this way control the course of the reaction as a whole. By making use of the
branched nature of the entire process, we can get considerable energies of coherent
emission with expenditure of small energies on initiation of the reaction. The
difference from the usual branching process is th.at the photon becomes not only the
reaction product, as in the conventional chemical laser, but also a direet par-
ticipant, ensuring development of the process.
Theoretical estimates show that chemical mixtures with a photonic branching mecha-
nism are possible in principle. For example a mixture of D2 + FZ + C02 +He + CHgF is
capable in princ iple of photonic branching, ensuring IR emission with energy ten
times as high as that of the radiation used for initiation [Ref. 42]. Other mix-
tures are also po ssible. Unfortunately in many cases detailed analysis is made
difficult by lack of data on the cross sections of elementary processes.
As a rule, the major problem in the case of photonic branching as well is stabili-
zation of prepared mixtures. It is possible that a technique for rapid mixing of
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reagents may be of assistance in solving this problem. In any event, the solution
of these problems depends to a great extent on further improvement of experimental
techniquea.
A few words on chemical lasers in the visible band. In this area, researchers have
come up againat considerable difficulties. The hopes for recombination lasers* are
not justified because of the small cross section of the recombination process. Some
other possibilities are analyzed in Ref. 43**. Most interesting among these seems
to be a chain reaction in a mixture of H2 + F2+ N2F4 producing Fxcited NF(1A) radi-
cals***. The difficulty to achieving lasing in this mixture is the low probability
of the transition NF(1A)-NF(3E-).
.1t the same time, chemical reactions are reliably known that lead to inversion and
in the final analysis to creation of an active medium. These are the reactions of
excited atoma that are extensively used in excimer lasers [Ref. 45, 461. But the
excited atoms in these lasers are obtained by the energy of an external source.
This is moet often an electron beam. Sources of W radiation are also used [Ref.
46]. Reactions of unexcited atoms are also known that lead to visible and ultra-
violet chemiluminescence with an appreciable quantum yield. This means that during
the reaction excited electron states arise, but either there is no inversion or the
gain is exceedingly small. The thought suggests itself that excited atoms can be
produced by collision or by absorption of a quantum of chemiluminescence by the
atoma due to the energy of an excited molecule produced in the reaction of unexcited
atoms [Ref. 47]. As the excited atom enters into a reaction, it will lead to popu-
lation inversion. Unfortunately, not a single specific reaction scheme that
realizes this idea has yet been suggested.
In the preface to Ref. 2 the editors state that most fundamental research, at least
that pertaining to HF, CO and iodine lasers, is in the concluding stage. The ma-
- terial presented here leads us to take exception to this statement. In any event,
thia is not the case as regards lasers based on a chain reaction of hydrogen or
deuterium fluorination. We can expect new and interesting advances.
The suthor takes this occasion to thank A. S. Bashkin, N. N. Yuryshev and colleagues
in groups under their leadership, and also V. I. Igoshin and V. A. Shcheglov for
cooperation.
REFERENCES
1. A. S. Bashkin, V. I. Igoshin, A. I. Nikitin, A. N. Orayevskiy, "Khimicheskiye
lazery. Itogi nauki i tekhniki. Ser. Radiotekhnika" [Chemical Lasers, Results
of Science and Technology. Radio Engineering Series], Vol 8, VINITI, Moscow,
1975.
2. "Handbook of Chemical Lasers" edited by R. W. F. Gross and J. F. Bott, a Wiley
Interscience Publication, 1976.
*See Ref. 1 and the literature cited there.
**This paper has a bibliography on the problems discussed there.
***Concerning this point, see also Ref. 44.
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3. A. N. Orayevskiy, "Khimicheskiye lazery. Spravochnik po lazeram" [Chem3cal
Lasers. A Handbook on Lasers], Vol 1, Chapter 1, "Sovetskoye radio", Moscow,
1978, p 158.
4. G. E~nanuel, W. G. Gaskill, R. J. Reiner et al., IEEE, QE-12, No 11, 1976, p 739.
5. A. N. Orayevskiy, V. P. Pimenov, A. A. Stepanov, V. A. Shcheglov, KVANTOVAYA
ELEKTRONIKA, Vol 3, No 1, 1976, p 136.
6. V. G. Krutova, A. N. Orayevskiy, A. A. Stepanov, V. A. Shcheglov, KVANTOVAYA
ELEKTRONIKA, Vol 3, No 9, 1976, p 1919.
- 7. A. A. Stepanov, V. A. Shcheglov, KVANTOVAYA ELEKTRONIKA, Vol 6, No 7, 1979,
p 1476.
8. N. G. Basov, A. S. Bashkin, V. I. Igoshin et al., PIS'MA V ZHURNAL EKSPERI-
MENTAL'NOY I TEORETICHESKOY FIZIKI, Vol 16, No 10, 1972, p 551.
9. A. S. Bashkin, A. N. Orayevskiy, N. M. Gorshunov et al., KVANTOVAYA ELEKTRONIKA,
- Vol 2, 1975, p 2092.
10. A. S. Bashkin, N. M. Gorshunov, Yu. A. Kunin et al., KVANTOVAYA ELEKTRONIKA,
Vol 3, 1976, p 1142.
11. A. S. Bashkin, N. M. Gorshunov, Yu. A. Kunin et al., KVANTOVAYA ELEKTRONIKA,
Vol S, 1978, p 2656.
12. A. S. Bashkin, N. M. Gorshunov, Yu. A. Kunin at al., Preprint FIAN, No 140,
1979.
13. W. E. McDermott, N. R. Pchelkin, D. I. Benard et al., APPL. PHYS. LETTS,
_ Vol 32, No 8, 1978, p 469.
14. D. J. Benard, "Ninth Winter Colloquium on Quantum Electronics," 8-10 January,
1979, Snow Bird, Utah.
15. H. H. Seliger, J. CHEM. PHYS., Vol 40, 1964, p 3133.
16. V. I. Igoshin, A. N. Orayevskiy, KRATKIYE SOOBSHCHENIYA PO FIZIKE, FIAN SSSR,
No 7, 1976, p 27. .
17. G. K. Vasil'yev, Ye. F. Makarov, A. G. Ryabenko, V. L. Tal'roze, ZHURNAL EKS- .
PERIMENTAL'NOY I TEORETICHESKOY FIZIKI, Vol 71, No 4(10), 1976, p 1320.
18. V. I. Igoshin, A. N. Orayevskiy, PIS'MA V ZHURNAL EKSPERIMENTAL'NOY I TEORE-
- TICHESKOY FIZIKI, Vol 21, 1975, p 235.
19. L. M. Peterson, G. H. Lindquist, C. B. Arnold, J. CHEM. PHYS., Vol 61, No 8,
1974, p 3480.
20. G. K. Vasil'yev, Ye. F. Makarov, A. G. Ryabenko, V. L. Tal'roze, ZHURNAL EKS-
PERIMENTAL'NOY I TEORETICHESKOY FIZIKI, Vol 68, No 4, 1975, p 1241.
32
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21. J. J. Hinchen, APPL. PHYS. LETTS, Vol 27, No 12, 1975, p 672.
22. V. I. Gur'yev, G. K. Vasil'yev, 0. M. Batovskiy, PIS'MA V ZHURNAL EKSPERIMEN-
TAL'NOY I TEORETICHESKOY FIZIKI, Vol 23, No S, 1976, p 256.
23. J. J. Hinchen, R. H. Hobbs, J. CHflrl. PHYS., Vol 65, No 7, 1976, p 2732.
24. N. C. Lang, J. C. Polanyi, J. Wanner, CHF:hiICAL PHYSICS, Vol 24, 1977, p 219.
25. G. K. Vasil'yev, V. I. Gur'yev, A. 0. Koval'skiy, ZHUR1vAL PRIKLADNOY SPEKTRO-
SKOPII, Vol 30, Na 6, 1979, p 1048.
26. J. J. Hinchen, R. H. Hobbs, J. APPL. PHYS., Vol 50, No 2, 1979, p 628.
27. R. L. Kerber, J. J. T. Hogh, APPL. OPTICS, Vol 17, No 15, 1978, p 2369.
28. Z. B. Alfassi, M. Baer, IEEE J. QUANTUM ELECTRON., QE-15, No 4, 1979, p 240.
29. N. G. Basov, A. S. Bashkin, P. G. Grigor'yev et al., KVANTOVAYA ELEKTRONIRA,
Vol 3, No 9, 1976, p 2067.
30. A. S. Bashkin, A. N. Orayevskiy, V. N. Tomashov, N. N. Yuryshev, KVANTOVAYA
ELEKTRONIKA, Vol 7, 1980, p 1357.
31. A. S. Bashkin, N. P. Vagin, 0. R. Nazyrov et al., KVANTOVAYA ELEKTRONIKA,
Vol 7, No 8, 1980.
32. A. S. Bashkin, A. F. Konoshenko, A. N. Orayevskiy et al., KVANTOVAYA ELEK-
_ TRONIKA, Vol 5, No 7, 1978, p 1608.
33. J. A. Mangano, R. L. Limpaecher, J. D. Daugherty, F. Russel, APPL. PHYS. LETTS,
Vol 25, No 5, 1975, p 293.
34. R. A. Gerber, E. L. Patterson, L. S. Blair, N. R. Greiner, APPL. PIiYS. LETTS,
Vol 25, No 5, 1974, p 281.
35. D. B. Nichols, R. B. Hall, J. D. McClure, J. APPL. PHYS., Vol 47, No 9, 1976,
p 4026.
36. V. I. Igoshin, V. Yu. Nikitin, A. N. Orayevskiy, KRATKIYE SOOBSHCHENIYA PO
FIZIKE, FIAN, No 26, 1978, p 20.
37. V. N. Kondrat'yev, Ye. Ye. Nikitin, "Kinetika i metchanizm gazofaznykh reaktsiy"
[Kinetics and Mechanism of Gas-Phase Reactions], Moscow, Nauka, 1974, p 443.
38. N. N. Senenov, "0 nekotorykh problemakh khimicheskoy kinetiki i reaktsionnoy
sposobnosti" [Concerning Some Problems of Chemical Kinetics and Reactivity],
USSR Academy of Sciences, Moscow, 1958.
39. G. K. Vasil'yev, Ye. F. Makarov, Yu. A. Chernyshev, DOKLADY AKADIIMII NAUK SSSR,
Vol 233, 1977, p 1118.
33
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40. V. I. Igoshin, V. Yu. Nikitin, A. N. Orayevskiy, KVANTOVAYA ELEKTRONIKA,
Vol 7, No 7, 1979.
41. N. G. Basov, Ye. P. Markin, A. N. Orayevskiy, A. V. Pankratov, DOKLADY AKADEMII
NAUK SSSR, Vol 198, No 5, 1971, p 1043.
42. V. I. Igoshin, A. N. Orayevskiy, KVANTOVAYA II.EKTRONIKA, Vol 6, No 12, 1979,
p 1912.
43. N. L. Kupriyanov, Dissertation, Physics Institute imeni P. N. Lebedev, USSR
Academy of Sciences, Moscow, 1979.
- 44. A. S. Bashkin, N. L. Kupriyanov, A. N. Orayevskiy, RVANTOVAYA ELEKTRONIKA,
Vol S, No 12, 1978, p 2611.
_ 45. V. A. Danilychev, 0. M. Kerimov, I. B. Kovsh, TRUDY FIZICHESKOGO INSTITUTA
IMENI P. N. LEBEDEVA, AKADEMII NAUK SSSR, Vol 85, 1976, p 49.
46. I. S. Datskevich, V. S. Zuyev, L. D. Mikheyev, I. V. Pogorel'skiy, KVANTOVAYA
ELEKTRONIKA, Vol 5, 1978, p 1456. '
47. A. N. Oraevsky, "Chemical Lasers: Present Situation and Trends," Preprint
FIAN, No 88, 1977.
COPYRIGHT: Izdatel'stvo "Nauka", "Izvestiya AN SSSR. Seriya fizicheskaya", 1980.
_ [8144/0285-6610]
6610
CSO: 8144/0285
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UDC 621.375.8
ABSTRACTS FROM THE COLLECTION 'OPTICALLY PUMPED GA5 LASERS'
Moscow GAZOVYYE LAZERY S OPTICHEKOY NAKACHKOY [TRUDY ORDENA LENINA FIZICHESKOGO
INSTITUTA IMENI P. N. LEBEDEVA ADAKEMII NAUK SSSR] in Russian Vol 125, 1980 pp 2,
218, 219
[Text) This collection presents the results of experimental and theoretical
research done in the Quantum Radio Physics Laboratory on the following major prob-
lems: photolysis oi gaseous compounds that contain bonds between the iodine atom
and elements of the fourth and fifth groups of the periodic table with discussion
df potential applications of the results to development of a recombination version
of the iodine laser and to separation of iodine isotopes; principles of forming,
amplifying and analyzing powerful nanosecond light pulses by iodine lasers, the
parameters of the experimental facility and questions of improving the character-
istics of the output emission; the working principle of a cooled photochemical Xe0
laser with pumping by the emission from a high-current open el ectric discharge, and
the outlook for further improving the output characteristics of such a lasery las-
ing by vapors of complex chemical compounds, and the prospects for using them as
active media in lasers with incoherent optical pumping; the vibrational structure
of the laser transition B2E~ - R2Et of the XeF molecule.
The publication is aimed at a broad class of scientists and engineers specializing
in the field of quantum radio physics.
UDC 621.37 5.826+535.342+535.372
LASING BY XeF WITH OPTICAL PUMPING, AND ANALYSIS OF THE SPECTRUM OF THE LASER
TRANSITION BZE~-X2E~
(Abstract of article by Zuyev, V. S., Kanayev, A. V., Mikheyev, L. D. and Stavrov-
skiy, D. B.]
[Text] The paper discusses the working principle of a photochemical XeF laser
(a z 350 nm). A laser is described that operates with pumping of the XeF2:N2(SF6):Ar
gas mixture by radiation from an open high-current discharge. Maximum lasing dura-
tion was 5 us, and maximum output energy was 0.15 J. An investigation was made of
the vibrational structure of the B2E�-X2E� transition as observed in the XeF mole-
cule in absorption, luminescence and~stimulated emission. The vibrational quantvm
and anharmonicity were measured in the upper and lower states: we = 308.7 cm- 1,
wexe =1.44 cm- 1, we = 225.7 cm- 1, wexe =11.0 cm- 1. The difference between equi-
lib rium internuclear distances of the XeF molecule is determined for the excited
(B) and ground (X) states: re - re = 0.33 � 0.01 A. Figures 12, references 63.
35
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UDC 621.373.8
LASCRS THAT USE VAPORS OF COMPLEX ORGANIC COMPOUNDS
[Abstract of article by Zuyev, V. S., Stoylov, Yu. Yu. and Trusov, K. K.]
[Text] A theoretical examination is made of the emission characteristics of lasers
based on ccmplex organic compounds in the quasi-steady state with consideration of
induced losses in the spectral region of lasing in a system of triplet and excited
singlet states of the molecLles. The results of the calculations are compared with
experimental data for POPOP and TOPOT vapor lasers. An investigation is made of
the thermal stability of these compounds at T< 600 K. The singlet-triplet con-
veraion constants and absorption cross sections of excited singlet molecules of
TOPOT in the lasing band were determined, and the effectiveness of using a buffer
gas to stabilize POPOP and TOPOT molecules was estimated. Figures 11, references
67.
UDC 621.378.8
EMISSION AND AMPLIFICATION OF NANOSECOND PULSES BY IODINE LASERS
jAbatract of article by Zuyev, V. S., Katulin, V. A., Nosach, V. Yu. and Petrov,
A. L.]
[Text] The paper gives the results of experimental research on iodine photolysis
high-power lasers with pumping by lamps and by the emission from high-current elec-
tric discharges. An investigation is made of the fundamental parameters of the
working medium, the parameters of lasers with bo th lamp pumping and electric dis-
charge pumping, and methods of shaping a short pulse with the directivity of lasing
at the diffraction limit. It is demonstrated that it is potentially feasible to
amplify a short pulse with an iodine amplifier pumped by a high-current open dis-
charge. An iodine laser is described that produces a pulse with duration of 1 ns,
divergence of 10-4 radian and energy of 100 J at a constrast of 108, and 300 J at a
contrast of 102-103. Figures 37, references 67.
UDC 621.373.8
A XENON OXIDE PHOTOCHEMICAL LASER
[Abbtract of article by Zuyev, V. S., Mikheyev, L. D. and Pogorel'skiy, I. V.]
[Text] The paper describes theoretical and experimental research on development,
creation and investigation of the peculiarities of a photochemical laser based on
xenon oxide, using photodissociation of nitrous oxide by the vacuum ultraviolet
emission of an open high-current discharge with formation of oxygen atoms and sub-
sequent oxidation of xenon. An examination is made of the theoretical problems
associated with substantiation of the mechanism and calcuYation of the kinetics of
phyeicochemical processes in the Xe0 laser. Pumping is numerically analyzed, and
invereion and gain on the laser transition are computed. The laser design is de-
scribed, and also the procedure used in experiments that give optimum temperatures,
composition and pressure of components of the working mixture yielding a lasing
energy of 2.2 J in a pulse from an active volume of about 1 liter. The spectral
36
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composition of the laser emission and the energy characteristics of the laser are
studied. The heat release during photolysis is estimated as well as the rate con-
stants of quenching of the upper laser state of Xe0 (21E+) and the vibrational re-
laxation of the lower atate of Xe0 (11E+). A theoretical investigation is made of
the internal losses in the active medium of a photochemical Xe0 laser. An estimate
is made of the feasibility of increasing the volume of the active medium by using a
plane-parallel cavity. Figures 20, tables 3, references 49.
UDC 621.375.826
INVESTIGATION OF PROCESSES OF PHOTOLYSIS OF COMYOUNDS WITH P-I AND As-I BONDS
[Abstract of article by Andreyeva, T. L., Birich, G. N., Sorokin, V. N., Struk,
L. I. and Suvorov, D. N.]
[Text] Detailed experimental studies are done on the parameters of lasing on the
transition 2PI12 2P312, a= 1.3 um of atomic iodine that arises upon photodissocia-
tion of molecules of (CF3)2AsI and (CF3)2PI. The light source was an IFP-5000
xenon flashlamp. On the basis of the resultant experimental data, a scheme is
deviaed for the principal reactions that accompany photolysis of molecules of
(CF3)zAsl and (CF3) 2PI and that determine the energy parameters of the stimulated
emiasion. Figures 8, table 1, references 18.
UDC 541.14
INVESTIGATION OF PROCESSES OF PHOTODISSOCIATION OF MOLECULES OF SiC13I AND SiF3I .
[Abstract of article by Andreyeva, T. L., Sorokin, V. N. and Struk, I. I.]
[Text] Experimental research is done on lasing on a transition of atomic iodine
that is stimulated upon photodissociation of molecules of SiC1gI and SiFgI. A
xenon-filled coaxial flashlamp of original design was used as the light source. _
An analysis is made of the principal chemical reactions that accompany photolysis
of molecules of SiC13I and SiFgI, and that determine the energy characteristics of _
the stimulated emission. Figures 10, references 10.
UDC 621.375.826
CUNCERNING POSSIBILITIES OF [FMISSION] IN THE VISIBLE BAND WITH PHOTODISSO CIATION
UF MOLECULES
[Abstract of article by Andreyeva, T. L.]
[Text] An analysis is made of lower excited states of some diatomic radicals and
atoms from which transitions to the gronnd GLate lie in the visible ar.d near ultra-
violet region of the spectrum. An examination is made of possible mechanisms of
~ formation of inversion upon photodissociation of molecules by radiation from a
source with continuous spectrum for which the brightness temperature is T- 3�104 K.
Figure 1, tables 2, references 27.
37
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UDC 621.378.33
REACTIONS OF IODINE ATOMS IN THE EXCITED [I* ( 2P 1/2) ] AND UNEXCITID [I ( 2P3/2) ]
STATES WITH PERFLUOROALKYL RADICALS
[Abstract of article by Andreyeva, T. L., Kuznetsova, S. V., Maslov, A. I. and
Sobel'man, I. I. ]
[Text] A method of studying reactions of excited and unexcited atoms is discussed
tha t is based on flash photolysis of molecules with simultaneous transillumination `
of the wcrking medium by resonant laser emission. The proposed technique is used
for studying reactions that accompany photolysis of molecules of RI (CFgI, p-C3F7I,
i-C3F7I). Rate constants are determined for recombination of iodine atoms into 12
in the presence of RI molecules for atoms of I(2P3/2) and I* (2P1/2), as well as the
constants for recombination of radicals R into R2, and for recombination of radi-
cals R with atoms of I* (2P1/2) and I(2P3/2) into the RI molecule. It is shown that
in reactions of recombination into 12 and RI, atoms of I(2P3/2) are much more active
than atoms of I* (2P1/2) � The authors discuss the part played by the investigated .
reactions in the kinetics of the flash photolysis laser. Results are compared with
data in.the literature. Figures 4, tables 7, references 43.
UDC 621.378.833
ON THE POSSIBILITY OF USING RECOMBINATION REACTIONS AND ALKALI METALS TO GET P0PTJ-
LATION I:dVERSION ON ATOMIC IODINE.
[Abstract of article tiy Andreyeva, T. L., Babkin, V. I., Maslov, A. I., 5obe1'man,
1. 1, and Yukov, Ye. A.]
(Text] The authors consider the feasibility of developing a continuous-flow ver-
sion of a laser using a transition of atomic iodine. Population inversion aXises
as a result of depletion of the lower laser levei due to preferred recombination
of iodine atoms in the ground state into molecules. Atoms of alkali metals are used
to get atomic iodine and free radicals without expending electric energy. It is
pro poaed that an electric discharge be used for exciting the atomic iodine. An
examination is made of the kinetics of the principal chemical reactions, and the
possibility of achieving inversion is demonstrated for reasonable parameters of the
working medium. A schematic diagram of the laser facility id discussed. Figures 3,
tables 2, references 14.
UDC 621.039.335+621.378.33
INVE5TTGATION OF THE FEASIBILITY OF SEPARATING ISOTOPES 1171 AND 1291 BY AN IODINE
P110TODISSOCIATION LASER
(Abstract of article by Andreyeva, T. L., Kuznetsova, S. V., riaslov, A. I., Sobel'-
man, I. I. and Yukov, Ye. A.]
[Text] A method of separating iodine isotopes is proposed that is based on the -
co nsiderable difference of the rate constants of reactions of excited I* (2P1,2) and
38
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unexcited iodine atoms with CF3 radicals and C1 molecules, and on the possibility
of using an iodine photolysis laser based on R117 I molecules (a = 1.315 um) to act
on 1271 atoms in states ZP1/2 and 2P312. An investigation is made of the feasibility
of isolating the pure 129I isotope and a mixture of 127I and 1291. Figures 6,
_ table 1, references 14.
COPYRTGHT: .Lzdatel'stvo "Nauka", 1980
(8-6610]
6610
CSO: 1862
A
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UDC 621.373.826
A PULSE-PERIODIC PHOTODISSOCIATIVE IODINE LASER PUMPED BY THE BADIATION OF MAGNETO-
PLASMA COMPRESSORS
Moscow KVANTOVAYA ELEKTRONIKA in Russian Vol 1,No 9(99),Sep 80 pp 2052-2054 manu-
script received 13 Mar 80
[Article by G. N. Kashnikov, V. K. Orlov, A. N. Panin, A. K. Piskunov and V. A.
Reznikov]
[Text] The authors study the characteristics of a photodissoci.a-
tive iodine laser pumped by magnetoplasma compressor emission.
The laser design uses a system of closed circulation of the C3F7I
working gas. A pulse-periodic operating mode is realized with an
interval of 1 minute between pulses, a lasing energy level of 110 J
and pulse duration of 30 �s.
In deaigns of photodissociative iodine lasers developed for nuclear fusion facili-
ties, the optical pumping source is either an open electric discharge [Ref. 1] or
xenon lamps that operate in the brief flash mode with duration of a few dozen micro-
seconds [Ref. 2]. In this type of excitation, the amplifying medium does not con-
tain shock waves that produce optical inhomogeneities and considerably. increase the
divergence of radiation at the output of the amplifier. To produce short electric
aupply pulses in these cases we must produce a voltage surge across discharge gaps
0.5-1 m long, which requires the development of high-voltage (U > 50 kV) and commu-
tating devices. .
The use of quartz optical pumping sources based on magnecoplasma compressors [Ref.
avoids these difficulties since the power supply in the short pulse mode is a
low-valtage battery (U = 3-5 kV), and discharge initiation (creeping discharge over
a surface a few centimeters long) is by a trigatron circuit where synchronous oper-
ation of any number of sources does not require commutators. By using such sources
in addition to lamps a system for closed circulation of the working mixture can be
realized in iodine lasers [Ref. 2], which considerably reduces the expenditure of
working gases when the laser is operated in the pulse-periodic mode.
The photodiasociative laser studied here consists of a working chamber with five
pumping sources based on magnetoplasma compressors perpendicular to the optical
axia in the middle plane of the reactor. The quartz container of each source is
50 mm in diameter. The chamber measures 1000 x 250 a 250 mm; it is equipped with an
optical window measuring 250 x 250 mm. Each compressor is supplied by an independent
capacitor bank with capacitance of 800 uF charged to 3.3 kV, discharge half-period
40
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ia t2 - 26 us, the attenuation constant of the loop is P= 4�104 s-1. The coef-
ficient of transfer of the energy stored in the loop to the plasma is 0.8. Dis-
charges of the magnetoplasma compressor were triggered by an ignition pulse (Ti =
2 u8, Ei = 1 J) with electrical separation into ten channels; the spread in firing
of dischargeg was about 1 us. Structurally, the cavities of the pumping sources
_ were interconnected, and removal of products of erosion was done by a vacuum pump
down to a pressure of about 5�10-2 mm Hg. The electric power supply system can
give discharges at a level of Est = 36 kJ once per minute. Attached to the reactor
_ is a syatem for closed circulation of the working mixture, shown schematically in
_ Fig. 1. This is made up of a flat cryostat installed in the working gas flow.
The cryostat has a recess at the top for liquid phase of the working substance.
The circulating blower, based on an induction motor, is located inside of the
working space.
j 4 LA Fig. 1. Diagram of system for closed ,
based on circulation of the magnetoplasma working compresfluid:sor; 1--
working spsce; 2--optical pumping source
- 3--
_ circulating blower; 4--cryostat; 5--

0 ~ ? ~ liquid phase of CgF~I
The working fluid was p-C3F7I diluted with SF6.
The reflectivities of the mirrors in the flat laser cavity were R1= 99%, R2 = 50%,
diameter 280 mm. Laser emission was directed by a lens with focal length of 1 m
and a reflecting plate to a TPI-2-5 calorimeter. Oscillograms of the emission
- pulses were recorded by an FD9E111 photodiode.
The maximum emission energy of the laser was Ee = 115 J for stored energy in tha
capacitors of 36 kJ, p-C3F7I pressure of 11 mm Hg and lOx dilution with SF6. The
efficiency of the facility was 0.29%, which is close to that of 0.25�6 achieved pre-
viously ou an iodine laser pumped with an open discharge at :he same stored energy
_ level [Ref. . 4].
With an increase in the length of the active region and improvement of the energy
parameters of the given type of laser as losses to the lasing threshold are re-
duced, there is a concomitant improvement in the laser parameters (efficiency of 1
and 1.4% with respect to invested energy in Ref. 1 and 5 respectively). Upon re-
peated initiation of the same mixture the lasing energy decreases due to buildup
of the molecular iodine and reduction in the pressure of the working componen,t
(Fig. 2, curve 1). The idea behind the system for closed circulation of the working
E, Rel, units
ro
B ' r~---
, � �
6 ~
4
Z o
0 2' 4 6 8 10 H
Fig. 2. Lasing energy as a function of the
number of pulses without replacement of the
working fJ.uid: PC3F7I = 11 mm Hg, pSF6 =110 mm Hg (1)
and with the use of a closed circulating system,
PSF6 = 110 mm Hg (2)
41
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r.
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fluid is removal of the IZ by freezing it out on a cooled surface, and restoration
of the pressure of the working component to the equilibrium level by evaporating
the p-C3F7I fram the liquid phase [Ref. 61..
An experiment with use of the closed circulating system was done in the following
~ arrangement. The working gas was let into the reactor to a pressure of 30 mm Hg,
the cryoatat was cooYed to -50�C, which corresponds to a p-C3F7I pressure of
10 mm Hg, and then SF6 was added to a pressure of 100 mm Hg and the closed circu-
lating system was sw itched on. The mixture was optically stimulated at a rate of
once per minute aC Egt= 36 J. Up to the fifth pulse the optimum pressure of the
working component was determined by variation of the cold trap temperature, and then
the temperature was stabilized at -40�C, which corresponds to a pressure of
pC3F7I = 23 mm Hg. The lasing energy in subsequent pulses was stable: Ee =110 J
(Fig. 2, curve 2). It should be noted that at such a C3E7I pressure, pumping
emission losses due to vignetting by the quartz sources amounted to about 1/3.
Fig. 3 shows oscillograms of lasing pulses recorded in two sections of the semi-
- transparent mirror. Close to the surface of the pumping sources the lasing pulse
shape (Fig. 3b) differed considerably from the pumping pulse shape. Close to the
wall of the reacCor, the lasing pulse shape (Fig. 3c) repeated the pumping pulse.
No interruption of lasing due to pyrolysis was observed over the entire end face
of the laser.
A
a
Fig. 3. Oscil lograms of magnetoplasma compressor
current pulaes (a), lasing pulses at the surface
of the pumping sources (b) and in the midsection b
of the space b etween the sources and the reactor
- w811 (C); Pr,3F7I =11 IDm Hg, PSF6' 110 mm Hg, WMM~
scale 10 us/div c
I
The proposed laser can be used as a signal amplifier for a master Q-switched laser.
Fo r spectral matching of the signals of the master laser and amplif ier, a method
can be uaed that provides for delivering the signal of the master laser at zero
cur rent of the magnetoplasma compressor of the amplifier [Ref. 1] when the magnetic
f ield in the amplif ier space ia minimum and displacement of the amplification line
is insignif icant.
REFERENCES
1. V. A. Katulin, V. Yu. Nosach, A. L. Petrov, KDANTOVAYA ELEKTRONIKA, Vol 3, 1976,
p 1829.
2. G. Bredlov, Ye. Fill, V. Fuse, K. Fola, R. Fol'k, Ye. Vitte, KVAN'I'OVAYA ELEK-
TRONIKA, Vol 3, 1976, p 906.
42
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3. A. S. Kamrukov, G. N. Kashnikov, N. P. Kozlov, V. K. Orlov, Yu. S. Protasov,
PIS'MA V ZHURNAL TEKHNICHESKOY FIZIKI, Vol 3, 1977, p 2334.
= 4. N. G. Baaov, L. Ye. Golubev, V. S. Zuyev, V. A. Katulin, V. N. Netemin,
0. Yu. Nosach, V. Yu. Nosach, A. L. Petrov, KVANTOVAYA ELEKTRONIKA, No 6, 1973,
p llb.
5. I. L. Yachnev, Author's abstract of candidate's dissertation, Leningrad,
State Optics Institute, 1978.
6. W. Fuas, K. Hohla, OPTICS COMMS, Vol 18, 1976, p 427.
COPYRIGHT: Izdatel'stvo "Sovetskoye radio", "Kvantovaya elektronika", 1980.
(13-6610]
6610
CSO: 1862
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UDC 621.373.8
CONCERNING THE CHANGE IN SHIELDING ACTION OF PRODUCTS OF THERMAL DISSOCIATION OF
MATERIALS UNDER THE EFFECT OF LASER IIrIISSION IN A MOVING MEDIUM
- Moscow KVANTOVAYA ELEKTRONIKA in Russian Vol 7, No 9(99), Sep 80 pp 2049-2051 manu-
script received 3 Mar 80
[Article by N. A. Kirichenko, A. G. Korepanov and B. S. Luk'yanchuk, Physics Insti-
tute imeni P. N. Lebedev, USSR Academy of Sciences, Moscow]
[Text] The paper discusses the feasibility af reducing the strong
shielding action of products of combustion of organic materials
produced by C02 laser emission by entrainment of dispersed carbon
in a gas stream under the action of a blast through the radiation-
affected zone.
Products of combustion of organic materials (soot particles, C02 molecules and so
_ on) strongly absorb radiation with a= 10.6 um. This phenomenon leads to increased
energy inputs when CO 2 laser radiation is used to treat such materials as wood,
- textolite and the like. In this connection it is of interest to study the feasi-
bility of reducing the screening action of combustion products by a blast through
the radiation-affected zone.
In the general case, the problem of combustion is quite complicated since it is
necessary to take cons ideration of a number of factors such as the energy released
during burning, heat exchange with the medium and so on. In this paper we consider
_ a simpler problem where the exothermal reaction can be disregarded. Such a situ-
ation may arise for example with thermal dissociation of organic molecules in an
inert atmoaphere under the effect of laser emission, or if the intensity of radia-
tion is great compared with the intensity of energy released by the reaction itself.
In the case of thermal dissociation of organic materials in an inert atmosphere
[Ref. 1], one of the major products of the process is dispersed carbon (soot).
Therefore let us assume for the sake of simplicity that the screening action of
the products of disso ciation is due entirely to dispersed carbon. In blasting,
the soot particles ar e entrained by the gas flow, which changes the screening
action.
The influence that cross blasting the radiation-affected zone has on the effective- -
ness of laser heating of inetals was studied in Ref. 2-4. However, these papers
= coneidered Che mechanical action of a stream of gases leading to the formation and
entrainment of liquid metal droplets due to the development of hydrodynamic
44
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inatabilities in a layer of inelt. The transverse movement of the stream produced
a greater rate of removal of material than in the case of direct vaporization since
part of the laser radiation energy was not expended on the latent heat of vaporiza-
tion. However, effects associated with a change in screening of the surface of the
material by products of laser destruction were not considered in Ref. 2-4. At the
same time, we know that the screening action of such products may be considerable
[Ref. 5, 6].
Consider the following model of the investigated effect. Assume that C02 laser
radiation flux with uniform distribution of intensity over the crosa section of a
beam of radius a is incident on the material of a target that occupies the half-
space z< 0. The target is blasted by a gas flow with velocity v directed parallel
to the surface. As shown by simple estimates using a method outlined in Ref. 6,
for the parameters of the problem that are interest to us, the dimensions of soot
particles Rp are usually _ 10-6 cm [Ref. 1, 7, 8], and in times of the order of
T�a/v the temperatures and velocities of the particles and those of the gas flow
become equal. Thereafter, the spatial distribution of soot particles changes as a
result of diffusion in the moving gas. In an approximation that assumes that the
sizes of all particles are the same (the actual size distribution of particles is
given in Ref. 1) and that their concentration 3.s fairly small, the problem is de-
scribed by by a system of equations of diffusion of particles in the gas and ther-
mal conductivity in the target material
an
DOn-u 0 x=rcosy, z>O,
ax_ -
(1)
- D andz l = Q (r. T) .
==o
AT=0,z< 0g
k ~z I ( l(r, ~)-T1(Tjsoo-Tm), r6a. (2)
:oo t-'1 (T j:_o -Tm), r> a,
ip)=1oeXPj-Q~R(r. z)dz 9(a-r). (3)
l o
Here r, 0, z are cylindrical coordinates; D= ksTw/67ruRp is the coefficient of
Brawnian movement of the soot particles; T. is the temperature of the gas stream;
_ u ia the coefficient of dynamic viscosity of the gas; k is the coefficient of
thermal conductivity of the material; Ip is the initial flux density of the radia-
tion (as z+-) .
The flux density of particles of soot leaving the surface is given with reasonable
accuracy by the expression [Ref. 9]
sT ~
Q=N4xo kgT exP - k
(4)
is the surface concentration of soot particles; c=(8kgT/Wm)' is the
where N- 41R T
average thermal velocity of the particles, corresponding to surface temperature T;
a= AO 0 6x0' p is the density of the material; pp = 2.25 g/cm3 is the density of
- ,.;:~�zphite; Ap = 46.9 �10-13 erg; xp = 4�10-8 cm are materi,al constants [Ref. 10].
45
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The cross section of radiation absorption by a small particle (2nRp/a� 1) is given
by the Mie formula [Ref. . 11
4-W1lIX-1 Im [(e-1)/(s-}'2% (5)
where s a(3.48 + 2.461)2 is the permittivity of soot on a wavelength of 10.6 um
[Ref. 12].
The coefficient of heat exchange n between the target and the moving gas stream
can be written as the sum of coefficients of molecular [Ref. 13] and convective
[ltef. . 14) heat exchange:
,i_~"~ V i + a.s3t ~ ~/'~i '�p`'i.' (b)
Here pr is gas density; R is the universal gas constant; A is atomic weight; K is
the coefficient of thermal conductivity of the gas; Re = vL/v is the Reynolds number
of the gas stream; Pr ss v/X is the Prandtl number; v is the coefficient of kinematic
viscosity of the gas; X is the coefficient of thermal diffusivity of the gas; L is
the distance from the edge of the plate to the point where n is calculated (if a�L,
n is independent of the coordinates in the region of interest to us).
By using finite Feurier transformation with respect to Hankel transformation
with respect to r and Fourier transformation with respect to z, system of equations
(1)-(3) can be r educed to a aystem of integral equations:
1= exp - a--~ id~~ 1 d2n exp 12Dr g-ilco~l)J X
o o x Ko(Zp u)Q iri, (7)
T = f 'idri ~ 4n 7 ~~i Z k k~ u )IJ + Ta..
8
Here we use the following notation: r= r/a; T= T/Tp; I= I/Ip; Tp = aIp/k; T./Tp;
Q' Q/QO ; 40 ` R(T - Tp); u=[r2 +rj - 2rr1 cos 4 -02) ]11; Kp is the cylindrical func-
tion of the imaginary argument; Hp is the Struve function; Np is the Neumann func-
tion [Ref. 15].
System of equat ions (7) was numerically solved on a computer by a method of suces-
sive iterations for values of the parameters a/ksT = 10; T�/Tp = 0.1. Fig. 1 shows
how the emission power that reaches the surface through the absorbing layer of soot
Farticles depends on the velocity of the blast without consideration of heat ex-
change, i. e. at rta/k = 0 and oQpa2/D = ZO4 (curve 1), 106 (2), 108 (3) and 1010 (4).
The stream is completely blown away when va/2D - 107, which corresponds to a gas
flow velocity v� 2 m/s (for particles with a size of Rp =10'6 cm, a= 1 cm) .
1
Fig. 2 illustrates the influence of heat exchange on the surface. The radiation
power that reaches the surface of the target is plotted as a function of the heat
46
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exchange parameter r1a/k for va/2D =103 and for the same values of the absorption
paxameter aQpa2/D as in Fig. 1. ~16
'%�0 1 ? 3 4
% Po
~
0 42 0,4 0,6 QB ya/k
Fig. 1 Fig. 2 Fig. 3
Shown im Fig. 3 at va/2D = 10, vQpa2/D =1010, na/k = 0 is the typical distribution
of radiation flux density with respect to radii of the zone of exposure that make
angles 0 s n7r/16 with the velocity vector of the gas stream. For angles 0 0.1 ms is usually greater than the time of passage of the medium
through the laser cavity. The characteristic time of diffusion mixing [Ref. 1]
tm sKF/D (F is the cross sectional area of the mixing jets; K is a factor that
characterizes the degree of intermixing; D is the coefficient of laminar or turbu-
lent diffuaion) can be shortened by reducing the cross section of the jets and
by turbulizing their boundaries. It is for this reason that efforts are made to
_ reduce the nozzle dimensions in gas jet mixing sys:.ems. Making jet mixing systems
with transverse dimension d= S mm in large-volune continuous-action facilities by
using arrays of miniature nozzles [Ref. 2, 3] is a complicated technical problem.
Gasdynamic perturbations on the boundaries of the jets lead to heating of the gas
stream [Ref. 4] and losses to relaxation.
A further step in the direction of reducing Tm is heterogeneous mixing of gas flows,
including flows of chemically reacting components, as proposed in Ref. 4-6. In
heterogeneous mixing a stream of aerosol particles measuring about 10 um is directed
tnto a shaped homogeneous flow of gas mixture with a predetermined chemical makeup
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and thermodynamic parameters. The particles penetrate deeply into the mixture and
are converted to gas as a result of aerodynamic heating. The time of molecular
mixing in the wakes of the particles may be reduced by a factor of more than 100 as
compared with gas jet mixing. Gasdynamic flow perturbations are also considerably
reduced. The use of heterogeneous mixing can appreciably improve the energy char-
acteristics of a C02 gasdynamic laser and enables discharge of spent gases into the
atmosphere. The difficulties of realiz ing such systems lie in the necessity for
developing fuels with combustion temperature of the order of 4000 K containing
products with a minimum content of quenching impurities [Ref. 3].
Ref. 7 discusses the possibility of an increase in working pressures in chemical
lasers as a result of laser pyrolysis in a mixture of fuel and oxidant. The reac-
tion of thermal dissociation of NaNg is given as an example, where atomic Na is
given off that is capable of initiating a reaction of hydrogen with halides at
ordinary temperatures.
In this paper we consider a method of producing a stream of active medium based on
gasdynamic pyrolysis of aerosol particl es of substances with reserve internal
chemical energy. This method enables improvement of the energy characteristics of
gasdynamic lasers through nonequilibrium chemical reactions. If a stream of
particles of such an aerosol is directed into a high-enthalpy subsonic or super-
sonic gas flow, the particles will be h eated by gasdynamic interactiou to the tem-
perature of chemical dissociation. Part of the internal energy of the initial sub-
stance will be carried off by the pr:)ducts of dissociation, which may be in chemi-
- cal and thermal nonequilibrium. Thus the problem is to ensure thermodynamic con-
- ditions conducive to chemical reactions and relaxation processes in the flow such
that there is a buildup of the donor gas that is the carrier of thermally non-
equilibrium excitation.
LeC us examine the feasibility of realizing the mett�od as exemplified by gasdynamic
pyrolysis of NaN3 aerosbl particles introduced into a flow of gas mixture contain-
ing molecules of N2, CO and C02.
It is shown in Ref. 8 that thermal dissociation of sodium azide produces N3 radicals
with density in the flow reaching 1013 cm'3. The rate constant of dissociation of
NaNg powders in g/cm2�s depends on the specif ic surface S of the particles and is
very strongly dependent on temperature of the process [Ref. 13]. In accordance
with Ref. 8 we will assume that thermal dissoc.iation of sodium azide leads to pro-
duction of electronically excited molec ules of N2 (3Eu) in the reaction
2 N,-�N:('EW)--2N, (lEi).
We will disregard the probable vibrational excitation of products in this reaction.
The further evolution of excitation in the system is quite fully described by the
following elementary processes:
N ~('E~ )'}'N~~E`)"` 2N2~Z~),
(2)
-}-CO (IE*) N.(lEi)~'CO l'1~.
(3)
N': (lE~)-~-CO'(lE+).
(4)
N, ('E�)-FCO,('E~)-' .
(5)
co(3rn+coeE 2co� ('E'),
(s)
+ (V,(1E`) -.CO' (iE+)-FNs(`E~) .
(7)
- +CO, (1 M+) - .
(8)
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I(OH 1.'l Te 3N1k4lNNGV0HC1'&H� 7[A)!-
cKOpocTN I ra. cM'/c I pnrypa
K1
5� l0-'1
[gj
K,