Apparatus verifies concepts of converting laser energy directly into electric energy. Mirror, placed in beam and inclined at angle to it, directs small amount of incident radiation to monitor which establishes precise power levels and other beam characteristics. Second mirror and condensing lens direct bulk of laser energy into laser plasmadynamic converter

Shimada, K.

English

NASA Technical Reports Server

August 1973	 B73-10853 
NASA TECH BRIEF 
NASA Pasadena Office	 C 
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. 
Laser Energy Converted into Electric Power 
The problem: 
To transmit electric power to remote receivers, 
such as space probes, installations atop mountains, etc. 
Ruby Laser
5% Mirror 
Condensing Lens 
-I Window -
Laser Beam I 
.	
Monitor
precise power levels and other beam characteristics. 
A second mirror and condensing lens direct the bulk 
of the laser energy into a laser plasmadynamic con-
verter (LPDC). 
Molybdenum 
Ion Collector
Electric 
Cs Insulator V0 
'E'^\ H
Load 
Stainless Steal 
Copper Cesium Reservoir 
The solution: 
Project a laser beam of sufficient power to the re-
mote site and then convert the laser energy directly 
into electric power. 
How it's done: 
The schematic diagram illustrates an experimental 
apparatus being used to verify the concepts of con-
verting laser energy directly into electric energy. The 
ruby laser provides 0.69 .tm (visible red) radiation at 
1 joule per pulse. A mirror, placed in the beam and 
inclined at an angle to it, directs a small amount of 
incident radiation to a monitor which establishes
The upper section of the LPDC is fabricated of a 
metal (molybdenum) which has a relatively high 
work function; the section is hemispherical in shape 
and is provided with a sapphire window and an ex-
ternal heater for precise temperature control of the 
inner surface. The lower section is shaped like an 
inverted cone with stainless steel sides and a copper 
apex which contains a reservoir of cesium (low work 
function). The two sections are insulated from each 
other and serve-as the electrodes of an electric power 
generator; the upper section is the positive electrode. 
(continued overleaf) 
	
Onis document was prepared under the sponsorship of the National
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	 will be free from privately owned rights.
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The LPDC operates as follows: After the laser 
energy passes through the condensing lens and the 
window in the LPDC, it impinges on the surface of 
the liquid cesium (somewhat obliquely so that no 
energy is reflected back along the incoming beam). 
The energy is at such a high density that it first 
vaporizes, then ionizes a quantity of cesium. When 
the density of the cesium plasma becomes sufficiently 
large, it absorbs all incoming energy and becomes 
almost completely ionized. The ions flow upward to 
the collector, and power can be extracted by an exter-
nal electric load connected to the LPDC electrodes. 
When an ion impinges on the upper electrode' which 
is maintained at a higher temperature than the cesium 
reservoir, it is neutralized and the neutral atom even-
tually is condensed on the walls of the cooler lower 
section and returned to the reservoir. Positively 
charged cesium ions constitute the source of current 
in an LPDC, whereas in a thermionic electric gener-
ator, current is induced by electrons which are boiled 
off from a cathode at high temperature. 
In the experimental device, the work function of 
the ion emitter (the pool of cesium) is 1.8 volts. The 
work function of the ion collector is 3.6 volts, so that 
the voltage output (V0) at the terminals of the LPDC 
is 1.8 volts if no voltage drop occurs within the 
LPDC. The output current depends on the size of the 
LPDC and the current density within the laser beam;
for a typical experimental device, a current density of 
approximately 10 A/cm2 could be realized. Also, such 
a cell has a theoretical efficiency of 40% if the cesium 
is 100% ionized and the output voltage is 1.8 volts. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: TSP 73-10353 
Patent status: 
Inquiries concerning the rights to the commercial 
use of this invention should be addressed to: 
NASA Patent Counsel 
Mail Code 1 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Source: Katsunori Shimada of 
Caltech/JPL
under contract to

NASA Pasadena Office 
(NPO-13308)
. 
B73-10353
	 Category 02


Laser energy converted into electric power

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