INVESTIGATION OF 2-WAVE MIXING IN ARBITRARY ORIENTED SILLENITE CRYSTALS

A generalized systematic description of the Two-Wave Mixing (TWM) proc ess in sillenite crystals allowing for arbitrary orientation of the gr ating vector is presented. An analytical expression for the TWM gain i s obtained for the special case of plane waves in a thin crystal(\g\d much less than 1) with large optical activity(\g\rho much less than 1, g is the coupling constant, rho the rotatory power, d the crystal thi ckness). Using a two-dimensional formulation the scope of the nonlinea r equations describing TWM can be extended to finite beams in arbitrar y geometries and to any crystal parameters. Two promising applications of this formulation are proposed. The polarization dependence of the TWM gain is used for the flattening of Gaussian beam profiles without expanding them. The dependence of the TWM gain on the interaction leng th is used for the determination of the crystal orientation. Experimen ts carried out on Bi12GeO20O crystals of a non-standard cut are in goo d agreement with the results of modelling.