Wedge immersed-thermistor bolometer measures infrared radiation in the atmosphere. The thermistor flakes are immersed by optical contact on a wedge-shaped germanium lens whose narrow dimension is clamped between two complementary wedge-shaped germanium blocks bonded with a suitable adhesive

Dreyfus, M. G.

English

NASA Technical Reports Server

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November 1965	 Brief 65-10330 
NASA TECH BRIEF 
NASA Tech Briefs are issued by the Technology Utilization Division to summarize specific 
technical innovations derived from the space program. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia, 22151. 
Wedge Immersed Thermistor Bolometer Measures Infrared Radiation 
The problem: To design a detector sufficiently 
sensitive to measure infrared radiation in the atmo-
sphere in the 15-micron CO2 absorption band. The 
measurements must be extremely precise because they 
are to be used in a method of inferring the vertical 
temperature structure of the atmosphere. In the 
employment of spectrometers, whose aspect ratios 
are other than unity due to entrance slit con-
figuration, the use of normal lens configurations 
results in spherical aberration and coma which 
detract from signal strength and quality. 
The solution: A wedge immersed-thermistor bob-
meter in which the thermistor flakes are immersed 
by optical contact on a wedge-shaped germanium lens
whose narrow dimension is clamped between two 
complementary wedge-shaped germanium blocks 
bonded with a suitable adhesive. This thermistor 
bolometer is placed behind the spectrometer entrance 
slit and the wedge configuration effectively forms a 
funnel that converges the incident energy on the 
thermistor flakes. Germanium is transparent to 
infrared energy and has a high refractive index. 
How it's done: The germanium wedge lens has a 
semispherical front surface with an aspect ratio of 
about 5:1. The narrow edge of the wedge extends 
into a holder formed by two germanium wedges 
spaced by thin pieces of plastic that may be in the 
form of buttons or strips. The assembly is held 
(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.
https://ntrs.nasa.gov/search.jsp?R=19650000328 2020-03-11T17:21:06+00:00Z
together by a suitable epoxy cement. An active 
thermistor flake and a precisely matched compensating 
thermistor flake are immersed in the thin edge of 
the wedge lens with an insulating layer of arsenic-
modified selenium. Electrical leads are connected to 
the thermistor flakes through areas of thinly 
deposited gold. The thinly deposited gold defines 
the active areas of the flakes that determine respons-
ivity. The two thermistor elements are connected in 
a bridge circuit across a constant-voltage source. 
The semiconductive thermistor flakes have an 
inherently high temperature coefficient of electrical 
resistance. Impinging radiation generates heat in the 
gold-coated areas of the flakes and the resultant 
change in resistance is measured by the bridge 
circuit and associated electronics.
Notes: 
I. This invention is not limited as to lens materials 
or optical radiation measured but may be operated 
with any optical. radiation including the visible 
and with any transparent lens material. 
2. This invention will effect marked improvement 
in noise equivalent power of a system in which 
the entrance pupil of the immersion optics has 
a high aspect ratio. 
3. Title to this invention (covered by U.S. Patent 
No. 3,119,086) has been waived under the pro-
visions of the National Aeronautics and Space 
Act (42 U.S.C. 2457 (1) ) to the Barnes Engineer-
ing Company, 30 Commerce Road, Stamford, 
Connecticut.
Source: Marc. G. Dreyfus of

Barnes Engineering Company

under contract to

Goddard Space Flight Center

(GSFC-443) 
Brief 65-10330	 Category 02


Wedge immersed thermistor bolometer measures infrared radiation

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