EVALUATION OF THE(Sanitized) PHASE II, TRIAL I GRATING

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04747A001500020011-2
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 2
• Document Creation Date: December 28, 2016
• Document Release Date: February 12, 2002
• Sequence Number: 11
• Content Type: MISC

Approved For Release 2002/06/17 : CIA-RDP78BO4747AO01500020011-2
STATINTL EVALUATION OF THE aPHASE II, TRIAL I GRATING:
It would be useful to test the grating in the system for which it
has been ruled, but it is by no means necessary. The specifications on
performance -- dealing with relative order intensities, energy distributions,
spacing, etc. -- are clearly spelled out in the viewer specifications.
The entire technical evaluation can be accomplished with an investigation
S of the Fraunhofer pattern of the grating. The optical system in the attached
sketch will provide the necessary means for the following tests which should
be performed:
1. Verification of grating spacing. Measurement of the separation
of the Fraunhofer orders will be sufficient to determine line frequency (to do
so requires the focal length of L2 to be known and a specific illuminating
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frequency used; in the case of a Mercury arc, the 5461 A line is the obvious
choice.)
2. Determination of energy distributions. A photometer in the
Fraunhofer plane can establish the strengths of the twelve (12) necessary
side orders relative to the central order. The strength of the central
order relative to the energy in the pattern without the grating provides
the reading necessary to establish the 3% minimum energy level. These
readings are then subjected to the three basic criteria which they must meet:
a) No more than a ratio of 1.4 in energy from order
to order.
b) No greater than a 2:1 fall-off from the brightest to
the least bright order.
c) 3% minimum energy in least bright order.
DECLASS REVIEW by NIMA/DOD
Approved For Release 2002/06/17 : CIA-RDP78BO4747AO01500020011-2
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Approved For Release 2002/06/17 : CIA-RDP78B04747A001500020011-2
3. Some additional things to look for (although they are not
explicitly covered in the specifications):
a) the presence of blaze in the rulings which tends to
put unequal energy into the same order-pair.
b) Evenness of ruling. and replication which can easily
be seen by masking out parts of the grating and examining some
relative intensities.
c) The presence of diffusing matter in the grating: it
should not diffuse or it defeats its purpose. A good, simple
test is to put the grating in contact against printed matter
and to observe the quality of its image.
Optical system for testing ratin Lenses Ll and L2 should
be used at no faster than f18, and focal length of L should be
consistent with the size of the point source to achi;ve the proper..
amount of coherence.
Approved For Release 2002/06/17 : CIA-RDP78BO4747AO01500020011-2