Optical distortions are eliminated by use of wetting agency followed by sequential immersion in several alcohol-water baths of increasing alcohol concentration. Dehydration proceeds uniformly over surface of gelatin. Dried plate is free of optically-distorting thickness variations

Stewart, W. C.

English

NASA Technical Reports Server

June 1975	 B75-10099 
NASA TECH BRIEF 
Marshall Space Flight Center S
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Dichromated-Gelatin Hologram Process for Improved Optical Quality 
fl
The problem: 
One form of optical distortion in dichromated-
gelatin holograms that are larger than a few 
centimeters in diameter is caused by thickness 
variations in the gelatin. These variations appear to be 
associated with local variations in the rate of 
dehydration of the swollen gelatin layer during 
development. 
The solution: 
The distortion is eliminated by the use of a wetting 
agent followed by sequential immersion in several 
alcohol-water baths of increasing alcohol concen-
tration. 
How it's done: 
The standard procedure for an exposed dichro-
mated gelatin hologram plate is to immerse it in water 
for approximately 5 minutes. The plate is then 
immersed in 100 percent isopropanol to remove the 
water from the gelatin layer. When the wet plate is 
first inserted into the isopropanol bath, random 
concentration gradients are observed at the surface of 
the gelatin layer as the residual water on the gelatin 
surface mixes with the isopropanol. At the completion 
of the development and drying process, the gelatin 
reticulation patterns are similar in shape and 
distribution to the previously-observed concentration 
gradients. These patterns are eliminated by adding 
steps to the development process.
After rinsing in water, the plate is immersed for 30 
seconds in a 1:200 bath of wetting agent in water. This 
leaves a thin uniform layer of water on the gelatin 
surface. The dehydration is accomplished in four 
additional steps. The plate is immersed and agitated 
for 2 minutes each in baths containing 50, 75, and 90 
percent isopropanol well mixed in water. The final 
bath is 100 percent isopropanol. In this way, the 
dehydration proceeds uniformly over the surface of 
the gelatin. The dried plate is free of the 
optically-distorting thickness variations. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
Marshall Space Flight Center 
Code ATO1 
Marshall Space Flight Center, Alabama 35812 
Reference: B75-10099 
Patent status: 
NASA has decided not to apply for a patent. 
Source: W. C. Stewart of

RCA Corp.
under contract to

Marshall Space Flight Center 
(MFS-23170) 
.
Categories: 03 (Physical Sciences) 
04 (Materials) 
This document was prepared under the sponsorship of the National
	
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Dichromated-gelatin hologram process for improved optical quality

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