Influence of the Bragg angle on the optimal energy exchange in the course of two-wave mixing in a Bi12SiO20 piezoelectric crystal

The problem of maximising the relative intensity of the signal optical wave in the course of two-wave mixing was solved taking into account the self-d iffraction in a Bi12SiO20 piezoelectric crystal. The maximisation was carri ed out simultaneously with respect to four parameters: the polarisation (ps i) and orientation (theta) angles, the crystal thickness d, and the Bragg a ngle phi. It was established that there are two sets of optimal parameters for a Bi12SiO20 crystal at the wavelength of 632.8 nm and for a typical acc eptor concentration of 10(22) m(-3): phi approximate to 11 degrees, theta a pproximate to 39.1 degrees, psi approximate to 98.85 degrees, d approximate to 7.11 mm (for the first maximum) and phi approximate to 11 degrees, thet a approximate to 320.9 degrees, psi approximate to 54.15 degrees, d approxi mate to 7.11 mm (for the second maximum). The dependences of these optimal parameters on the acceptor concentration in the range 10(21) -4x 10(22) m(- 3) were found. The model proposed for two-wave mixing in the special case o f a fixed Bragg angle and the constant visibility approximation improved th e agreement between the theoretical results and the known experimental data .