DIFFRACTION GRATINGS FOR DIRECT IMAGE VIEWER

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04747A001700010007-6
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 12
• Document Creation Date: December 28, 2016
• Document Release Date: April 24, 2001
• Sequence Number: 7
• Content Type: REPORT

 Approved For Release 2001/05/11 : CIA-RDP78BO4747AO01700010007-6
DIFFRACTION GRATINGS
for
DIRECT IMAGE VIEWER
Report on Phase II
Trial #2
STATOTHR
Declass Review by NIMA/DOD
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1.0 The Diamond Tool
Two diamond tools were made, using the same fixturing
and measuring equipment developed for trial #1. Some
difficulty was encountered due to the doubled size of
the tool required, and the problem of measuring to the
same accuracy over twice the distance.
2.0 The Ruling Set Up
The same procedure was used as for trial #1, in that
test grooves and test areas were ruled and over-ruled
under various conditions of tool orientation and
loading. The aluminum coating for ruling had to be
twice as thick as previous, and we were successful
in making the thicker coating without having excessive
surface roughness. It was found that the ruling engine
gearing necessary for ruling the required groove spacing
of 72.4u was incommensurate. Mathematically, the
combined gear ratio was an unending decimal. This
meant that the gearing could never be returned for
over-ruling. Therefore the test ruling had to be
ruled at the nearest possible commensurate interval,
namely 73.33u. It was felt that this change of 1%
would not affect the value of the test ruling. If and
when the final 10 inch rulings are made, we will then
be able to rule at the prescribed interval of 72.4u.
2.1 Set Up Control
We were fortunate to have available a new interference
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microscope received here just prior to the actual
set-up. Due to the new microscope and the increased
groove size, we were able to measure and photograph
the groove contour with interference fringes in air.
This removed the conversion problem and possible errors
in determining just what the wavelength really is in an
oil medium. A new and much more accurate method for'
measuring fringe location was worked out. This
consisted of orienting the fringes parallel to the
grooves and then measuring the parallel fringe micro-
interferogram using a contour projector. Sample.
micro-interferograms are included with this report,
along with a graph plotted from information obtained
from the micro-interferogram as measured with a
contour projector. For comparison this graph also
includes a curve which is a true arc, calculated.
from the measured width and depth of the groove.
3.0 Ruling and Replication STATOTHR
A master ruling ) was made, using the double
ruling techniques. The ruled area is 53x53 and on
a 58x58mm blank. Three transmission replicas of this
ruling were made on blanks 53x58xlOmm thick. The 3rd
replica was second generation so that we could
compare it to a 1st generation replica.
4.0 Grating Tests
The distribution of energy among the orders of the
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transmission replicas was measured, and for six
discrete wavelengths in steps of 10mu, between 500
and 550mu. The results were plotted*on a bar graph
included with this report. The sum of adjacent orders
is also -clotted on the bar graph to simulate the
energy distribution as the grating will actually be
used.
4.1 Test 4.0 was also simulated numerically and computed,
assuming a theoretically correct groove shape. Results
were plotted on a bar grpah for comparison to 4.0,
along with a plot of the sum of adjacent orders.
5.0 Test Results
As determined graphically from the micro-interferograms,
the groove contour departs from a true are by 0.07u.
However the groove is much more symmetrical than our
1st trial. Departure from symmetry, maximum, is O.Olu.
Also the groove contour closely resembles an oblate
concave curve as a smooth symmetrical curve should
perform well. For comparison, trial #2 is about six
times more symmetrical than trial #1.
5.1 The measured energy distribution among the orders for
transmission grating; #995 was examined for variation of
the important ratios between them. Unlike the previous
ruling, there is not much change of ratio with wave-
length. The following table gives the maximum ratios
for adjacent orders and for the highest vs lowest order.
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The ratios include both measured and calculated
theoretic values for the orders and for six discrete
wavelengths.
Wavelength
Measured Ratios
Theoretical Ratios
Adjacent orders - Hi Lo orders Adjacent orders Hi Lo orc.ers
5000A
5100A
5200A
5300A
5400A
5500A
1.73/1
2.00/1
2.16/1
2.13/1
1.95/1
1.75/1
2.32/1
2.26/1
2.16/1
2.17/1
2.3 0/1
2.24/1
1.52/1
1.52/1
1.52/1
1.59/1
1.54/1
1.58/1
1.91/1.
1.81/1
1.92/1
2.00/1
1.92/1
2.22/].
Since this grating will be used with adjacent orders
overlapping, the following table gives the ratios for
this case.
Wavelength
Measured Ratios
Theoretical Ratios
Adjacent orders-Hi/Lo orders
Adjacent orders-Hi Lo orc.ers
5000A
1.48/1
2.07/1
1.37/1
1.70/1
5100A
1.34/1
1.92/1
1.39/1
1.71/1
5200A
1.37/1
1.97/1
1.43/1
1.76/1
5300A
1.42/1
1.99/1
1.4.7/1
2.02/1
5400A
1.47/1
1.91/1
1.35/1
2.36/1
5500A
1.48/1
1.83/1
1.35/1
2.64/1
5.1.1 The above table shows that in some cases the test
ruling exceeds theory and in all cases closely
approaches theory. While it is not obvious from the
tables, there is the possibility of improving the
ratios still more by choosing the best wavelength
range. This is because the worst cases as picked,
for the table above, change their positions in the
orders as the discrete wavelengths are changed.
This is particularly true for adjacent orders.
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5.1.2 We have also calculated the relative luminosity of
each of the averaged orders over the wavelength
range 500-550 millimicrons.
5.2 The second generation transmission replica was
measured and the order energy distribution compared
to that for the first generation. When compared
order for order, the average difference in energy
was only 3.6% of the energy in each order.
Theoretical calculations predicted no difference
between first and second generation and the data
above bears this out within experimental accuracy.
6.0 Conclusions and Recommendations
We feel that test #2 is successful beyond our
fondest expectations. Original design goals
are met or exceeded in all respects. The energy
distribution in the orders is more uniform than
theory in the best cases and in the worst cases
is 91% of theory for adjacent orders and 82a of
theory for the overall order energy ratio. We
therefore recommend proceeding to Phase III,
the manufacture of a 10xlO inch ruling and
associated replica gratings.
The following are appended to this report:
1. Micro-interferograms of groove profile and
graphs plotted from micro-interferograms .
2. Bar Graph - Calculated order intensities for
discrete wavelengths and calculated order
intensities where adjacent orders are added.
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3. Bar Graph - Measured order intensities for
discrete wavelengths and measured order
intensities where adjacent orders are added.
!}. Bar Graph - Relative luminosity vs order for
the Bandpass 500-550 millimicrons.
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