Laser-induced spatial structures in a chemically active gas-phase medium illuminated by annular diffracting beams

The laws governing the propagation of diffracting beams in a two-component gaseous mixture are investigated on the basis of a computer simulation. It is discovered that several regions with high concentrations of the reaction product form. It is also found that the beam focus can move both in the direction of beam propagation and in the counter direction, and the change in its position can occur abruptly. It is shown that as time goes on, a high concentration of the reaction product is achieved in the central unilluminated region of the medium near the entrance cross section on account of diffusion (i.e., a diffusional concentration growth occurs). This leads to the formation of a dynamic concentration maximum in this region of the medium. Zh. Tekh. Fiz. 68, 8–14 (March 1998)