Fourier transform hologram camera increases the velocity range for holography by a factor of 10 to 1000. Two different optical systems, using a triangular arrangement of beam splitters and a mirror to illuminate the object from two directions, are investigated

Dyes, W. A.

Mc Cabe, B. J.

Ward, J. H.

English

NASA Technical Reports Server

September 1970	 Brief 70-10371 
NASA TECH BRIEF 
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Holographic Photography of High Velocity Particles 
.,, Laser Head 
CflhIIfl,2t
I 
Object
ri Splitter 
- -r t- - - ll\
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-	 - 
	
	 - - - Ill,	 _--	 5-. 
I 11r 
	
-	 — -	 Hologram Plane 
	
Transform Lens	 Prisms 
Figure 1. Camera System with Coincident Front and Back Focal Points 
A Fourier transform hologram camera has been 
designed that is capable of obtaining stationary images 
of high velocity particles. The primary advantage of 
the system is its ability to record objects moving with 
such high velocities that they move even during the 
short flash duration of a pulsed laser. Consequently, 
this camera increases the velocity range for hologra-
phy by a factor of 10 to 1000. 
Two different optical systems have been investi-
gated. Both use a triangular arrangement of beam 
splitters and a mirror to illuminate the object from 
two directions. Forward-diffracted light becomes 
the object beam, producing a Fourier transform of 
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
the object in the focal plane of a lens, and back-reflec-
ted light is used as the reference beam. These two 
beams remain mutually coherent as the object is 
moved. Hence, the primary optical design problem is 
to produce a fixed angle between the two beams, while 
maintaining a stationary interference pattern in the 
Fourier transform plane. 
In the design shown on Figure 1, two symmetrical 
optical systems are arranged so that both front and 
back focal points are coincident and the optical axes 
are inclined at an angle. With the object near the 
intersection of the two front focal planes, the forward-
diffracted light travels through the lower optical sys-
-	 (continued overleaf) 
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.
https://ntrs.nasa.gov/search.jsp?R=19700000358 2020-03-17T00:45:15+00:00Z
. 
Beam 
-
Transform	
Hologram 
	
M	
Point	
Lens	
Plane 
icroscope Lens  Source I	 Interferometer I	 I 
CollimatedLaser-	 Object1	
Bearn	
-	 rror 
Splitter 
	
Beam	 Plane  
Figure 2. Test Setup for Modified Mach-Zehnder Interferometer System 
with Coincident Back Focal Planes 
tern, while back-reflected light is collected primarily 
by the upper system. 
In order for this system to yield a stationary holo-
gram, the object's direction of motion must be per-
pendicular to the two axes and parallel to the inter-
section of the two front focal planes, within a very 
close tolerance. A similar situation occurs in any con-
figuration where the object and reference-beam focal 
planes are inclined. Since such systems produce a 
stationary image only in a special case, they were not 
experimentally investigated. 
Figure 2 diagrams a test setup using a better optical 
system for holography of moving objects, in which a 
modified Mach-Zehnder interferometer is placed 
between the object and the transform lens. In addition 
to the diffracted wave from the object, a point ref-
erence source is produced in the object plane- by a 
microscope lens. Apertures block the reference beam 
in the lower arm and the object diffracted beam in the 
upper arm. The final beam splitter is displaced slightly 
from its usual position, producing linear interference 
fringes in the back focal plane of the transform lens. 
Since parallel beams enter the lens, the front focal 
planes are parallel and the intensity in the hologram 
plane remains stationary, independent of the object's 
direction of motion. This has been verified experi-
mentally. 
The final optical system for the hologram camera 
uses the interferometer of Figure 2 with a plane polar-
ized laser beam and the triangular illumination scheme 
shown on Figure 1. A 1/4-wave plate is used in one 
leg of the triangle to rotate the plane of polarization 
of the forward diffracted beam by 90 degrees. An 
analyzer in the upper arm of the interferometer passes 
the reflected reference beam, while in the lower arm,
an analyzer passes the diffracted beam. A second 
1/4-wave plate then rotates the plane of polarization 
back again, so that interference can take place. 
Notes: 
1. Due to limitations on the resolution intrinsic to 
Fourier transform holography, the interferometer 
approach appears useful only for high-speed 
particles 100 microns in diameter or larger. These 
techniques may interest persons who study rela-
tively large, high-velocity particles such as those 
in wind tunnels and accelerated systems. 
2. The following documentation may be obtained 
from:
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.65) 
Reference: 
NASA-C R-86 147 (N69-24927), Feasibil-
ity Study of Velocity Synchronized Fou-
rier Transform Hologram Camera Sys-
tem 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546. 
Source: J. H. Ward, W. A. Dyes,

and B. J. McCabe of
Technical Operations, Inc.

under contract to

Electronics Research Center

(ERC- 10318)
S 
S 
Brief 70-10371	 Category 03


Holographic photography of high velocity particles

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