Gas dynamic laser

Gas Dynamic Laser (GDL) is laser based on differences in relaxation velocities of molecular vibrational states. The laser medium gas has such properties that an energetically lower vibrational state relaxes faster than a higher vibrational state, thus a population inversion is achieved in a particular time.

Pure Gas dynamic lasers usually use a combustion chamber, supersonic expansion nozzle and CO₂ as a active laser medium in mixure with nitrogen or helium. Gas dynamic laser could be however pumped not only by combustion, but by any adiabatic expansion of gas. Any hot and compressed gas with appropriate vibrational structure could be utilized.

Explosively pumped gas dynamic laser is a version of gas dynamic laser pumped by expansion of explosion products. Hexanitrobenzene and/or tetranitromethane with metal powder is preferred explosive. This device could have very high pulse peak power output aplicable in laser weapons.

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Function

1. Hot compressed gas is generated.
2. Gas expands through subsonic or supersonic expansion nozzle, the temperature of the gas becomes lower and according to maxwell–Boltzmann distribution the gas isn't in thermodynamic equilibrium until the vibrational states relax.
3. 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.
4. Gas flows through mirror area where stimulated emission takes place.
5. Gas returns to equilibrium and becomes warm. It must be removed from the laser cavity or it will interfere whith the thermodynamics and vibrational state relaxation of the freshly expanded gas.

Application

Proposed laser rifle design SAVATTI[1] also uses gas dynamic laser principle.

Almost any chemical laser uses gas-dynamic processes to increase it's efficiency.

High energy efficiency (as high as 30%) and very high power output makes GDL perspective for some (especially military) applications.

See also

• Gas laser
• Chemical laser
• Carbon dioxide laser

References

• Laser History - Gasdynamic[2]
• LEOT Laser Tutorial - Course 3: Laser Technology - Module 9: CO2 Laser Systems[3]
• Laser History - Airborne Star Wars Laser [4]
• United States Patent 4099142 : Condensed explosive gas dynamic laser [5]