6A7 - On self-trapping of a laser beam

When a sufficiently intense light beam propagates in an isotropic medium, the latter becomes birefringent with refractive index dependent on the even powers of the electric field strength. The permittivity also increases with the refractive index. Under such conditions, at very high intensities, a new effect arises: the light beam produces a kind of dielectric waveguide embracing that part of the medium where the dielectric permittivity has undergone an increase. At sufficient power of the beam the diffracted light is totally reflected on the walls of this waveguide, and is unable to escape outwards; thus there arises a self-trapping "channel." By means of an electronic computer, data for calculating the function
D = f(P)
are obtained,
D
being the diameter of the self-trapping channel, and
P
the power of the light beam entering the medium. The shape of
D = f(P)
as computed numerically reveals a number of interesting features which are discussed and analyzed in detail.