Section of light pipe consists of separated segments having opposed toroidal mirrors that intercept meridional rays to present virtual wall in space between mirrors, thus insuring uninterrupted light transmission down the pipe. Design affords internal access to pipe section. Segments are electrically or thermally insulated from one another

Young, N.

English

NASA Technical Reports Server

Virtual Wall
November 1970	 Brief 70-10632 
NASA TECH BRIEF H 
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 progam may be directed to the Tech-
nology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Toroidal Mirrors Provide Virtual Walls for Breaks in Light Pipes 
The problem: 
To effect a circumferential break or separation in 
a light pipe without introducing aperture losses and in-
terrupting or obstructing the continuity of the light 
beam. Such a break is required for insertion of meas-
uring probes, choppers, and samples into the light 
pipe.
, 
The solution: 
A section of light pipe consisting of separated 
segments having opposed toroidal mirrors that will 
intercept meridional rays to present a virtual wall 
in the space between the mirrors, thus ensuring 
uninterrupted transmission of the rays down the pipe. 
How it's done: 
Each segment of the light pipe in the open section 
has a flange with a machined and polished surface to
form a toroidal mirror. The center of the generating 
arc (radius r) of each toroidal surface is at the inter-
section of the opposite generating arc with the inside 
diameter of the light pipe. With this geometry, me-
ridional rays incident on one toroidal mirror are re-
flected by the other so that the incident and reflected 
rays intersect at points defining a virtual wall of 
nearly constant diameter (approximating that of the 
inside diameter of the light pipe proper). As the toroi-
dal mirrors are surfaces of revolution about the longi-
tudinal axis of the light pipe, they are axially symmetri-
cal and off-axis meridional rays of even large angles 
will be propagated down the pipe. 
Notes: 
I. In addition to affording internal access to a light pipe 
section (e.g., for insertion of measuring devices, 
samplers, choppers, etc.), this design allows the 
segments to be axially rotated when required and 
also to be electrically or thermally insulated from 
one another. 
2. No additional documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Patent status: 
No patent action is contemplated by NASA. 
Source: Niels Young of 
Block Engineering, Inc. 
under contract to 
Ames Research Center 
(ARC-10031) 
Category 03 
rc	 Ames Research Center 
Mail Stop N-240-2 
Moffett Field, California 94035 
Reference: B70-10632 
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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Toroidal mirrors provide virtual walls for breaks in light pipes

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