Laser beam profile deformation effect during Bragg acousto-optic interaction: a non-paraxial approximation

It is commonly known that the spatial profiles of the diffracted light beam s during Bragg acousto-optic interaction are distorted due to the Bragg ang le selection mechanism. All the conventional studies on this effect use the paraxial approximation. But this approximation should be amended when the incident angle of the light is large enough that the diffracted light waves do not propagate closely along the optic axis of the acousto-optic diffrac tion system. By using a spatial Fourier transform approach, we rigorously s tudy the light beam profile deformation effect of the diffracted light duri ng the Bragg acousto-optic interaction beyond the paraxial approximation. S tarting from the wave equation, a set of coupled-wave equations is derived to depict the acousto-optic effect. Analytic solutions that describe the pr ofiles of the diffracted light are derived from the acousto-optic coupled-w ave equations. From the solutions, differences can be found between the one s with and without paraxial approximation. (C) 1999 Society of Photo-Optica l Instrumentation Engineers. [S0091-3286(99)00107-5].