Heat-rejection telescope windows reflect incident solar energy outside the hydrogen-alpha line while processing a peak transmission exceeding fifty percent at 6563 angstrom units. The windows also function as secondary blocking filters to the telescope's Fabry-Perot filter

Austin, R.

Rehnberg, J.

English

NASA Technical Reports Server

NASA TECH BRIEF 
0
September 1970
	 Brief 70-10386 
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 Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Heat-Rejection Windows for Telescopes 
Heat-rejection windows have been constructed for 
telescopes to reflect incident solar energy outside the 
hydrogen-alpha line while processing a peak trans-
mission exceeding 50% at 6563 A. The original require-
ment was telescope windows for monitoring of the 
solar disk at the hydrogen-alpha line; they were to 
reduce the solar heat load at the entrance apertures of 
the telescopes. 
The newly designed window comprises two ele-
ments mounted in a cell of aluminum alloy. The outer 
element is primarily an ultraviolet reflector transmit-
ting visible and near-infrared incident solar energy. 
The inner element bears a multilayer dielectric coating 
that transmits 80% of incident sunlight in a 300-A 
passband centered near 6563 A.. Energy beyond the 
main spectral band is almost wholly reflected (re-
flectance is 0.99 between 4100 A and the far infrared). 
A window's secondary function is as a secondary 
blocking filter to a telescope's Fabry- Perot filter. 
Fused silica is the substrate of both elements; it 
was chosen for its transmission properties and its 
resistance to browning by radiation. The outer ele-
ment is made necessary by the fact that the -high-index 
dielectric material on the inner one shows considerable 
absorption at wavelengths shorter than 4000 A. Coat-
ings have been uniformly deposited over 8-in.-diam 
clear apertures with equipment for automatic control 
of rate and thickness. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B70-10386 
Patent status: 
Inquiries about obtaining the rights for commercial 
use of this invention- may be made to NASA, Code 
GP, Washington, D.C. 20546. 
Source: R. Austin and J. Rehiiberg of
Perkin-Elmer Corp.
under contract to
Marshall Space Flight Center
(M FS-20634) 
Category 04 
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.
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Heat-rejection windows for telescopes

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