Nonlinear diffraction of light beams propagating in photorefractive mediawith embedded reflecting wire

摘要

The theory of nonlinear diffraction of intensive light beams propagating through photorefractive media isdeveloped. Diffraction occurs on a reflecting wire embedded in the nonlinear medium at a relatively smallangle with respect to the direction of the beam propagation. It is shown that this process is analogous to thegeneration of waves by a flow of a superfluid past an obstacle. The "equation of state" of such a superfluid isdetermined by the nonlinear properties of the medium. On the basis of this hydrodynamic analogy, the notionof the "Mach number" is introduced where the transverse component of the wave vector plays the role of thefluid velocity. It is found that the Mach cone separates two regions of the diffraction pattern: inside the Machcone oblique dark solitons are generated and outside the Mach cone the region of "optical ship waves" (thewave pattern formed by a two-dimensional packet of linear waves) is situated. Analytical theory of the "opticalship waves" is developed and two-dimensional dark soliton solutions of the generalized two-dimensionalnonlinear Schrodinger equation describing the light beam propagation are found. Stability of dark solitons withrespect to their decay into vortices is studied and it is shown that they are stable for large enough values of theMach number.