Propagation of a light pulse in a moving two-level absorbing medium

A solution is obtained for the equations describing the passage of a monochromatic radiation pulse of arbitrary shape I₀(t) across a two-level absorbing medium with an activeparticle density N₀ = const. It is shown that, depending on the ratio of the velocity of the medium v(t) to v₀ = 2I₀/N₀, two modes of propagation of bleaching waves can be observed and the boundary between these modes is v = v₀. The treatment is applicable to a radiation source moving at an arbitrary velocity in an absorbing medium.