Spectroscope incorporates two prisms combined with holographic grating as dispersing element. This provides high dispersion with selective undeviated wavelength. Prisms with different indices of refraction and/or angles for construction and reconstruction may be used. Also, different prisms for input and output may be used

Franke, J. M.

English

NASA Technical Reports Server

Beam Two 
Beam One 
Collimated
Monochromatic
Beam
Reconstructed 
Beam 
Zero-Order 
Beam 
Collimated
Monochromatic
Beam
Reconstructed 
Beam 
Baffle (c) Addition of Second Prism 
Monochromatic
Collimated
Beam Zero-Order 
Beam 
baffle 
Polychromatic
Collimated
Beam 
June 1975	 B75-10090 
NASA TECH BRIEF 
Langley Research Center
	
cl 
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. 
Holographic Direct-Vision Spectroscope 
Film Plane 
(a) Construction of Hologram
Baffle	 rio og ram 
(b) Reconstruction
n
Baffle	 (d) Illustration of Dispersion: A1>A2>A, 	 Baffle 
Combined Prisms and Holographic Grating for Direct-Vision Spectroscope
(continued overleaf) 
This document was prepared under the 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=19750000090 2020-03-19T20:07:16+00:00Z
A simple direct-vision spectroscope has been 
designed and tested at Langley Research Center. The 
spectroscope incorporates two prisms combined with 
a holographic grating as the dispersing element. This 
provides high dispersion with a selective undeviated 
wavelength. 
The operation of the holographic direct-vision 
spectroscope is best understood by examining the 
construction of the holographic grating (see illus-
tration). A collimated monochromatic beam, incident 
on the two faces of the prism, is split into two beams 
which cross at the film plane (a). A high-resolution 
film plate is placed in the film plane to record the 
interference pattern. The spacing between the lines is 
simply the wavelength of the light divided by twice the 
sine of half the angle between the two beams. 
The film is developed and placed back in its 
original position. The lower face of the prism is 
blocked, and a collimated beam incident on the upper 
face of the prism is refracted by the prism, producing 
only one beam (b). This beam is partially diffracted by 
the holographic grating, forming two beams. The 
zero-order beam is the attenuated beam passing 
straight through the hologram while the reconstructed 
beam is formed by the diffracted energy. These beams 
are directly analogous to beams one and two (a). 
A second prism is added as shown (c). Collimated 
light, having the same wavelength as the construction 
light, will have entering, reconstructed, and zero-
order beams which are parallel. The entering and 
reconstructed beams are collinear. 
If the entering light is not monochromatic or is not 
of the same wavelength as the light used for 
construction, the reconstructed beam or beams will 
not be collinear with the entrance beam but will be 
dispersed about it according to wavelength (d). 
Shorter wavelengths will be diffracted less and longer 
wavelengths will be diffracted more than the
wavelength of construction. The exit angle of the 
zero-order beam is independent of wavelength. The 
amount of dispersion is dependent on the line spacing 
of the holographic grating. The line spacing is 
dependent on the angles and the index of refraction of 
the prism used for construction. 
The undeviated wavelength is the same as the 
construction wavelength if the construction and 
reconstruction prisms are identical. Construction is 
easiest with laser light as it is characteristically 
monochromatic and coherent. For wavelengths for 
•which lasers are not available, several alternate 
schemes of construction may be used separately or 
combined. Prisms with different indices of refraction 
and/or angles for construction and reconstruction 
may be used. Also, different prisms for the input and 
the output may be used. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
Langley Research Center 
Mail Stop 139-A 
Hampton, Virginia 23665 
Reference: B75-10090 
Patent status: 
Inquiries concerning rights for the commercial use 
of this invention should be addressed to: 
Patent Counsel 
Langley Research Center 
Mail Stop 313 
Hampton, Virginia 23665 
Source: John M. Franke
Langley Research Center

(LAR-1 1750)
. 
S 
B 75-10090	
Categories: 03 (Physical Sciences) 
04 (Materials)


Holographic direct-vision spectroscope

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server