Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Gas Dynamic Laser 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 mixture 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 applicable in laser weapons.