Steady-state thermal self-focusing of laser beams

Some aspects of the theory of thermal self-focusing of cw laser beams are considered. A geometrical-optics ray equation is derived for a nonlinear absorbing medium. This ray equation is used to construct the aberration pattern in thermal self-focusing. The structure of the focal region is also analyzed. A detailed discussion is given of the behavior of the field at the focus for a wide range of the values of the absorption in the medium and the input power. The stability of steady-state thermal self-focusing is investigated and it is shown that such self-focusing can be applied to real high-power beams without splitting them into separate filaments.