Formation of a longitudinal particle density gradient in velocity-selective laser photodissociation

An analysis is made of the formation of a longitudinal density gradient of particles formed by laser photodissociation of gases, as a result of velocity-selective excitation. Numerical estimates are given for two variants: direct dissociation and two-photon dissociation via an intermediate level. In some cases the inhomogeneity caused by this effect can appreciably exceed the equilibrium density of product particles. This effect can be used in laser photochemistry (particularly microchemistry) and can also be used as a method of population inversion.