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 fi ...

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 is achieved in a particular time. It was invented by Edward Gerry and

Arthur Kantrowitz Arthur Robert Kantrowitz (October 20, 1913 – November 29, 2008) was an American scientist, engineer, and educator. Kantrowitz grew up in The Bronx and graduated from DeWitt Clinton High School.Overbye, Dennis"Arthur R. Kantrowitz, Whos ...

at Avco Everett Research Laboratory 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, 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 ...

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 The active laser medium (also called gain medium or lasing medium) is the source of optical gain within a laser. The gain results from the stimulated emission of photons through electronic or molecular transitions to a lower energy state from a h ...

. 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. Combus ...

adiabatic expansion In thermodynamics, an adiabatic process (Greek: ''adiábatos'', "impassable") is a type of thermodynamic process that occurs without transferring heat or mass between the thermodynamic system and its environment. Unlike an isothermal process ...

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 Hexanitrobenzene, also known as HNB, is a high-density explosive compound with chemical formula , obtained by oxidizing the amine group of pentanitroaniline with hydrogen peroxide in sulfuric acid. Properties HNB has the undesirable property o ...

and/or tetranitromethane with metal powder is the preferred explosive. This device could have very high pulsed peak power output suitable for laser weapons.

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 use ...

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 the ...

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 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 prov ...

or it will interfere with the thermodynamics and vibrational state relaxation of the freshly expanded gas.

Application

Almost any

chemical laser A chemical laser is a laser that obtains its energy from a chemical reaction. Chemical lasers can reach continuous wave output with power reaching to megawatt levels. They are used in industry for cutting and drilling. Common examples of chemical ...

uses gas-dynamic processes to increase its efficiency. High energy efficiency (as high as 30%) and very high power output make GDL suitable for some (especially military) applications.

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

Function

Application

See also

References