Holograms of large objects may be formed by using several coherent low-intensity laser sources. If several low intensity laser sources are available, they can be applied simultaneously. Each source is then used to establish one object beam and one reference beam whose path lengths are equal, recording a small portion of the total object

Kurtz, R. L.

English

NASA Technical Reports Server

Lase 
Source
Coherence Length Extender
October 1973
	
.	 B73-10399 
•	 NASA TECH BRIEF 
Marshall Space Flight Center 
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. 
Coherence-Length Extender 
. 
.
The problem: 
To form a hologram of a large object, the laser 
sources used must produce beams that are intense 
and have the maximum possible coherence length. In 
general, the available laser sources cannot provide both 
at the same time. Therefore, holograms of large objects 
have been limited by the coherence and intensity 
capabilities of the available laser sources. 
The solution: 
Holograms of large objects may be formed by using 
several coherent low-intensity laser sources.
How it's done: 
In holography, the maximum coherence length from 
any given laser source can be obtained by equating the 
lengths of the reference and object beams. The setup 
shown in the figure utilizes this principle with three 
beams. In each instance, the total length of the object 
beam is equal to the total length of its respective refer-
ence beam. There is sufficient overlap between the 
adjacent beams to produce uniform brightness over the 
entire object image. 
The total number of object beams necessary to 
record the entire object is determined by the dimension 
(continued overleaf) 
This documentwas prepared underthe Sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19730000399 2020-03-17T07:28:51+00:00Z
of the object and the coherence length of each laser 
source. Here the coherence length of each source is just 
sufficient to record one section of the object, labeled d. 
As shown, three sources are necessary to record the 
entire object. 
It is noted that each separate reference beam is 
incident on the film at a different angle. Therefore, on 
reconstruction with a single reference beam, the plate 
must be rotated back and forth through some small 
angle, & where 
where a, 13, and y were the original angles associated 
with the three reference beams used for construction of 
the hologram. 
If several low intensity laser sources are available, 
they can be applied simultaneously by a method similar 
to that in the figure. Each laser source is then used to 
establish one object beam and one reference beam whose
path lengths are equal, recording a small portion of the 
total object. When used in this fashion, the drift 
between the lasers is inconsequential since the object 
beam from the first source interferes only with the 
reference beam from the second, and so on. 
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Code A&PS-TU 
Marshall Space Flight Center, Alabama 35812 
Reference: B73-10399 
Patent status: 
NASA has decided not to apply for a patent. 
Source: R. L. Kurtz
Marshall Space Flight Center 
(MFS-22434)
. 
B73-10399	 Category 03


Coherence-length extender

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server