Pulsed ruby laser emits two optical frequencies simultaneously so holographic recordings of test object give images showing desired range contours. Process enables generation of contour maps for practical applications such as gaging size and shape of mechanical parts and other structures

Heflinger, L. O.

Wuerker, R. F.

English

NASA Technical Reports Server

December 1971	 Brief 71-10534 
NASA TECH BRIEF 
Ames Research 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. 
Multifrequency Laser Beams for Holographic Contouring 
The problem: 
To generate contour maps with contour intervals of 
the order of a few millimeters for practical applica-
tions such as gaging the size and shape of mechanical 
parts or of structures such as parabolic antennas. 
Light 
Ref lector
boundary of the cavity; the other end is defined by 
optical means for selecting at least two frequencies, 
each within the lasing linewidth. Illumination of the 
object by light of two adjacent, distinct frequencies 
generates the desired range contours on the holo-
graphic image of the object. The distance between 
adjacent range contour lines is determined by the 
S
Beamspl itter 
Negative	 Negative/
	
Optical Cavity 
Object	 L ns Lens -- 
Light	 I 
Diffuser \	 I	 I 
Fl 
Resonant	 Laser	 Light,/
Reflector Reflector 
Hologram 
The solution: 
By using a pulsed ruby laser which emits two 
optical frequencies simultaneously, holographic re-
cordings of the test object give images covered with 
the desired range contours. 
How it's done: 
The holographic apparatus comprises a pulsed 
laser with a given lasing linewidth and optical means 
for pumping the laser. The optical cavity of the laser 
includes a reflector for the monochromatic light de-
veloped by the laser. The reflector defines one end or
frequency difference between the two light waves. 
The hologram is obtained by splitting the laser light 
into a reference beam and a scene beam; the refer-
ence beam is directed onto the hologram, and the 
scene beam is first directed onto the object and then 
onto the hologram. 
The laser depicted in the diagram is a ruby rod 
pumped by a helical flash lamp. Alternatively, the 
laser may be of any other type which permits pulsed 
operation with high power, and has an equivalent 
lasing linewidth (of the order of 0.025 nm), for ex-
ample, a neodymium laser.
(continued overleaf) 
This documetct 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.
https://ntrs.nasa.gov/search.jsp?R=19710000524 2020-03-17T02:26:57+00:00Z
The boundary of the optical cavity is formed by 
the light reflector which may be a mirror, with a di-
electric coating at its plane front surface, that reflects 
substantially all of the light, say 99%. The other end 
of the optical cavity may be formed by a Fabry-Perot 
etalon or resonant reflector; the resonant reflector may 
be either a single slab of sapphire or two slabs of 
quartz. The resonant reflector selects two closely ad-
jacent frequencies within the lasing linewidth of the 
laser. It is shown as forming one end of the optical 
cavity; however, a suitable, partially reflected mirror 
may also be used to define the cavity, whereupon the 
resonant reflector may he disposed anywhere within 
the cavity. 
The laser in the diagram operates in a conventional 
manner and develops an output beam which impinges 
on the beamsplitter, and is split into a reference beam 
and a scene beam. The reference beam is reflected 
by the front surface of the beamsplitter and then en-
larged by the negative lens to a size which fills the 
entire area of the hologram after reflection from the 
light reflector a front-surface mirror of aluminum). 
The scene beam may also be enlarged by a negative 
lens prior to falling on the object. The light scattered 
by the object is then also recorded on the hologram 
Interference between the waves scattered from the 
object and the reference beam is recorded as ampli-
tude and phase of the scattered scene beam and per-
mits reconstruction of the object by the light of a 
suitable reference beam. 
The light diffuser is optional; it is constructed so as 
to ensure that the apparent light source does not 
appear too large, and preferentially scatters in the
forward direction. It may be fabricated from ground 
glass with a thin coating of lacquer that has the same 
index of refraction as the ground glass. The hologram 
is a suitable photographic film or plate. 
Notes: 
1. The following documentation may be obtained 
from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $8.00 
(or microfiche $0.95) 
Reference: 
NASA CR-114274 (N71-17271), 
Holographic Instrumentation Studies. 
2. No additional information is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: B71-10534 
Patent status: 
Title to this invention has been waived under the 
provisions of the National Aeronautics and Space Act 
[42 U.S.C. 2457(f)] to the TRW Systems Group, TRW, 
Inc., One Space Park, Redondo Beach, California. 
Source: Lee 0. Heffinger and Ralph F. Wuerker of

TRW Systems Group, TRW, Inc.

under contract to

Ames Research Center 
(ARC-10341)
. 
S 
Brief 71-10534	 Category 03


Multifrequency laser beams for holographic contouring

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