Lasers may be made with higher energy photons than heretofore possible. It has been proposed that vacuum ultraviolet lasing can be obtained by bombarding superfluid helium with electron beam, while coupling acoustic energy into helium to set up standing waves in fluid

Saffren, M. M.

English

NASA Technical Reports Server

June 1975	 B75-10118 
NASA TECH BRIEF 
NASA Pasadena Office 
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. 
High-Energy Lasers by Using Distributed Reflection: A Concept 
S
A new concept suggests that lasers may be made 
with higher energy photons than heretofore possible. 
It has been proposed that vacuum ultraviolet (VUV) 
lasing can be obtained by bombarding superfluid 
helium with an electron beam, while coupling acoustic 
energy into the helium to set up standing waves in the 
fluid. 
VUV radiation is known to be generated when a 
stream of electrons bombard superfluid helium (He 
II). The key to this proposed technique is a method of 
reflecting the generated photons back and forth to 
produce a coherent beam. Neither mirrors nor any
other currently used techniques will reflect photons 
with wavelengths much lower than 1,700 A. (VUV 
radiation is around 800 A.) This has been the major 
stumbling block preventing the development of 
high-energy lasers such as VUV or X-ray. 
In the proposed VUV laser, acoustically-induced 
standing waves with a wavelength fundamentally or 
harmonically related to the VUV wavelength intro-
duce a spatial periodicity into the optical properties of 
the helium fluid. This should cause "distributed" 
reflection of the radiation by Bragg scattering as 
opposed to the discrete reflection that occurs at mirror 
Tank
vuV Path of	 I	 Electron Beam Holding Laser	 Photons	 I	 Source Hell Energ	
I	 I	 I 
(Superfluid)
Electron 
Beams 
Fluid 
Surface 
/ 
/ 
Spaced Apart at 
Super	
Standing Waves 
VUV Wavelength 
nsuiation	 (Wavefronts are
'< 
	
Perpendicular to	 stical 
	
Bottom of Tank)	 Transducer 
S Vacuum-Ultraviolet Laser
(continued overleaf) 
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https://ntrs.nasa.gov/search.jsp?R=19750000118 2020-03-19T20:05:48+00:00Z
surfaces. This method of producing lasing has already 
been proved in thin-film, solid-state injection lasers. 
The standing-wave, helium laser concept is 
illustrated in the figure. A tilted tank of superfluid 
helium is contained in a cryostat. An acoustic 
transducer on one wall of the tank is used to set up the 
standing waves, and an electron beam source above 
the tank bombards the helium. The electrons excite 
metastable states in the helium. Radiation from these 
states is reflected back and forth between the standing 
waves, and because of the geometry of the tank, a 
coherent beam of photons will be emitted from the 
liquid at an angle 900 from the standing waves. The 
special periodicity of the fluid may also cause the 
lasing species in the He II to assume the same 
periodicity as the acoustic waves. This would result in 
a self-sustaining, distributed-feedback laser in which 
the lasing is sustained without the continuous 
application of acoustic energy. 
Several variations to this basic system are possible. 
For instance, if the electron beam is applied nearly 
parallel to the He II surface, it may couple directly 
with the generated laser radiation. The result is 
amplification such as that which occurs in traveling-
wave devices. Also the periodicity could be generated 
by another laser instead of acoustic waves.
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak-Grove Drive 
Pasadena, California 91103 
Reference: TSP75-101 18 
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Inquiries concerning non-
exclusive or exclusive license for its commercial 
development should be addressed to: 
Patent Counsel 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Source: Melvin M. Saifren of 
Caltech/JPL
under contract to

NASA Pasadena Office

(NPO- 13346)
I 
. 
B75-10118	 Category: 03 (Physical Sciences)


High-energy lasers by using distributed reflection: A concept

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