A gas dynamic laser (GDL) is a
laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...
based on differences in relaxation velocities of
molecular vibrational states. The lasing medium gas has such properties that an energetically lower vibrational state relaxes faster than a higher vibrational state, and so a
population inversion
In science, specifically statistical mechanics, a population inversion occurs while a system (such as a group of atoms or molecules) exists in a state in which more members of the system are in higher, excited states than in lower, unexcited energ ...
is achieved in a particular time. It was invented by
Edward Gerry
Edward is an English given name. It is derived from the Anglo-Saxon name ''Ēadweard'', composed of the elements '' ēad'' "wealth, fortune; prosperous" and '' weard'' "guardian, protector”.
History
The name Edward was very popular in Anglo-Sax ...
and
Arthur Kantrowitz at
Avco Everett Research Laboratory
Avco Corporation is a subsidiary of Textron which operates Textron Systems Corporation
and Lycoming.
History
The Aviation Corporation was formed on March 2, 1929, to prevent a takeover of CAM-24 airmail service operator Embry-Riddle Compa ...
in 1966.
"History of Gas Lasers, Part 1—Continuous Wave Gas Lasers"
''Optics & Photonics News''. Retrieved 4 June 2013
Pure gas dynamic lasers usually use a combustion chamber, supersonic expansion nozzle
A nozzle is a device designed to control the direction or characteristics of a fluid flow (specially to increase velocity) as it exits (or enters) an enclosed chamber or pipe.
A nozzle is often a pipe or tube of varying cross sectional area, a ...
, and CO2, in a mixture with nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
or helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
, as the laser medium.
Gas dynamic lasers can be pumped by combustion
Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combusti ...
or adiabatic expansion of gas. Any hot and compressed gas with appropriate vibrational structure could be utilized.
The explosively pumped gas dynamic laser is a version of GDL pumped by expansion of explosion products. Hexanitrobenzene and/or tetranitromethane
Tetranitromethane or TNM is an organic oxidizer with chemical formula . Its chemical structure consists of four nitro groups attached to one carbon atom. In 1857 it was first synthesised by the reaction of sodium cyanoacetamide with nitric acid.
...
with metal powder is the preferred explosive. This device could have very high pulsed peak power output suitable for laser weapons
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The firs ...
.
Function
# Hot compressed gas is generated.
# Gas expands through subsonic or supersonic expansion nozzle, the temperature of the gas becomes lower and according to Maxwell–Boltzmann distribution
In physics (in particular in statistical mechanics), the Maxwell–Boltzmann distribution, or Maxwell(ian) distribution, is a particular probability distribution named after James Clerk Maxwell and Ludwig Boltzmann.
It was first defined and used ...
the gas isn't in thermodynamic equilibrium
Thermodynamic equilibrium is an axiomatic concept of thermodynamics. It is an internal state of a single thermodynamic system, or a relation between several thermodynamic systems connected by more or less permeable or impermeable walls. In thermod ...
until the vibrational states relax.
# The gas flows through the tube of a particular length for a particular time. In this time lower vibrational state does relax but higher vibrational state doesn't. Thus population inversion is achieved.
# Gas flows through mirror area where stimulated emission
Stimulated emission is the process by which an incoming photon of a specific frequency can interact with an excited atomic electron (or other excited molecular state), causing it to drop to a lower energy level. The liberated energy transfers to th ...
takes place.
# Gas returns to equilibrium and becomes warm. It must be removed from the laser cavity An optical cavity, resonating cavity or optical resonator is an arrangement of mirrors or other optical elements that forms a cavity resonator for light waves. Optical cavities are a major component of lasers, surrounding the gain medium and provi ...
or it will interfere with the thermodynamics and vibrational state relaxation of the freshly expanded gas.
Application
Almost any chemical laser uses gas-dynamic processes to increase its efficiency.
High energy efficiency
Energy efficiency may refer to:
* Energy efficiency (physics), the ratio between the useful output and input of an energy conversion process
** Electrical efficiency, useful power output per electrical power consumed
** Mechanical efficiency, a ra ...
(as high as 30%) and very high power output make GDL suitable for some (especially military) applications.
See also
* Gas laser
* Chemical laser
* Carbon dioxide laser
References
*Laser History - Gasdynami
*LEOT Laser Tutorial - Course 3: Laser Technology - Module 9: CO2 Laser System
*Laser History - Airborne Star Wars Lase
*United States Patent 4099142 : Condensed explosive gas dynamic lase
Chemical lasers
Gas lasers
Military lasers
{{Chemical lasers