Two holograms, made simultaneously, one with a red light component and one with the harmonic UV component to give two fringes in the UV construction due to shortened wavelength. The reconstruction, obtained with a He-Ne laser, could be photographed separately, giving quality interferograms

Heflinger, L. O.

English

NASA Technical Reports Server

December 1969	 Brief 69-10662 
NASA TECH BRIEF	 1 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Two-Color Holography 
Photographs of the two reconstructions from a single holographic interferogram of a projection lamp. The 
hologram was exposed simultaneously by the doubled and primary radiation from a Q-switched ruby laser. 
The filament of the lamp was heated between the two exposures, producing optical path length changes in the 
filling gas. Both images were reconstructed with a helium neon laser. The 0.6943 micron image is on the left. 
The other is the 0.347 micron or 'doubled" image. 
An important reason for the interest in holograms 
made with ultraviolet light is that smaller changes are 
visible because the shorter wavelength doubles the 
number of fringes in the holographic interferograms. 
Holograms have been made with uv radiation ob-
tained by second harmonic generation in a KDP
crystal fed with red light from a 0-switched ruby 
laser. The figure shows an example of a double-
exposed holographic interferogram. This holographic 
interferogram was made by first exposing the plate 
with the lamp filament heated to a dull glow, causing 
density changes in the heated filling gas. The new 
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
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aspect of this hologram is that two holograms are 
made simultaneously, one with the red light com-
ponent (6943 A) and one with the harmonic uv 
component (3471 A). Two fringes are seen in the 
uv construction due to the shortened wavelength. 
Since both reconstructions were obtained with the 
6328 A beam from a He-Ne laser, the angle at which 
the uv construction occurs is approximately double 
that of the red construction. As a result, the two 
could be photographed separately. 
The holographic arrangement consisted of a laser 
illuminator which included a 0.50-inch diameter x 
3.75-inch long 60° ruby rod of high homogeneity, a 
nitrobenzene Kerr-cell 0-switch, an air-spaced Glan 
polarizer, and a one-centimeter diameter intercavity 
aperture. The optical resonator consisted of a 99% re-
flectivity, dielectric-coated optical flat and an output 
sapphire resonant-reflector. The laser emitted a 0.75 
J pulse of red radiation of 50 nsec duration; this 
was sufficient energy to record a hologram on a 
full 4 x 5-inch plate. The output of the laser was 
passed through a KDP doubler, oriented to maximize 
the generation of uv radiation. Tests showed that the 
5% conversion efficiency of the uv radiation was 
sufficient to expose the full plate area. 
The combined beam from the laser was expanded 
by a simple lens and then divided into "scene" and 
"reference" beams by an elementary holocamera 
consisting of a glass beam splitter and three front-
surface mirrors. A ground glass was placed 13.5 cm 
from the photographic plate in one beam; the light 
bulb scene was placed between the plate and the 
ground glass screen. Red holograms were made by 
placing, before the output of the doubler, a pair of 
filters which absorbed 99% of the uv energy; uv-only 
holograms were made by using a pair of red absorbing
filters. For simultaneous red and uv holography, 
plates of partially absorbing uv glass were placed at 
the output of the doubler to balance the relative ex-
posure. 
An interesting observation made while viewing the 
hologram is that the angular orientation sensitivity 
of the plate is less for the uv (±23°), than it is for 
the red (±11°). This difference is apparently due to 
the absorption of the gelatin which rendered the ef-
fective thickness of the emulsion only 2.5 i in con-
trast to the 11 micron thickness of emulsion utilized 
by the red. 
The results demonstrate that doubling the ruby light 
is a practical method for gaining a factor of two in the 
sensitivity of holographic interferograms. By con-
structing a holocamera with uv grade optics, quality 
interferograms should be possible. 
Note: 
No additional documentation is available. Spe-
cific questions, however, may be directed to: 
Technology Utilization Officer 
Headquarters 
National Aeronautics 
and Space Administration 
Washingtor, D.C. 20546 
Reference: B69-10662 
Patent status: 
Inquiries about obtaining rights for the commer-
cial use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546. 
Source: Lee Opert Heflinger of 
TRW Systems Group
under contract to
NASA Headquarters 
(HQN- 10349)
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Two-color holography

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