Device was developed which produces short optical pulses of variable lengths with high peak power and without use of external modulators or independent light beams. Optical field intensity is built up inside cavity. At peak of its intensity, light is switched off

Szoke, A.

English

NASA Technical Reports Server

December 1972
	
B72-10655 
•	 NASA TECH BRIEF 
NASA Headquarters 
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. 
A Bi-Stable Optical Device 
The problem: 
Short optical (laser) pulses produced by Q switching or 
mode locking are difficult to change or control. 
The solution: 
A device has been developed which produces short 
optical pulses of variable lengths with high peak power 
and without the use of external modulators or inde-
pendent light beams.
absorber in the cavity at a pressure of 1 Ton. The first 
mirror of the Fabry-Perot cavity acts as the stationary 
mirror of the laser . cavity. The laser medium is pumped 
and Q-switching is initiated by the rotating mirror. When 
the intensity of the input current in the laser medium 
builds up to a specified value, there is a sudden transmis-
sion through the cavity and a pulse is produced at the 
output with a physical length of twice the laser cavity 
length. This length is equal to the distance between the 
Reflecting 
Stationary 
.4 First Mirror Second Mirror 
Saturable 
Absorber 
SF 6
 Gas 
Output Beam 
Rotating 
Mirror
Fabry-Perot
Cavity 
.
How it's done: 
Short optical pulses of variable length may be gen-
erated by a light-switching technique which uses the 
apparatus shown in the diagram. The optical field in-
tensity is built up inside the cavity. At the peak of its 
intensity, the light is switched off. 
Typically, the laser might be a CO 2 gas laser operating 
on the 106-um wavelength with SF 6 gas as the saturable
rotating mirror and the reflecting mirror of the cavity. 
Therefore, by controlling the length of the laser cavity, an 
easy method of producing optical pulses of variable length 
is obtained without the use of expensive external modu-
lators. This was difficult to accomplish by the prior 
Q-switching art due to the dependence of pulse width on 
laser gain, loss, pumping rate, and mirror reflectivity. 
(continued overleaf) 
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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.
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Note: 
Requests for further information may be directed to 
Technology Utilization Officer 
NASA Headquarters 
Code KT 
Washington, D. C 20546 
Reference: TSP72-10655
Patent status: 
NASA has decided not to apply for a patent. 
Source: A. Szoke of
Massachusetts Institute of Technology

under contract to

NASA Headquarters
(HON-10701) 
B72-10655	 Category 03.


A bi-stable optical device

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