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-diffraction in a Bi12SiO20 piezoelectric crystal. The maximisation was carried out simultaneously with respect to four parameters: the polarisation (Ψ) and orientation (θ) angles, the crystal thickness d, and the Bragg angle φ. 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 acceptor concentration of 1022 m-3: φ ∼ 110, θ ∼ 39.10, Ψ ∼ 98.850, d ∼ 7.11 mm (for the first maximum) and φ ∼ 110, θ ∼ 320.90, Ψ ∼ 54.150, d ∼ 7.11 mm (for the second maximum). The dependences of these optimal parameters on the acceptor concentration in the range 1021 - 4 x 1022 m-3 were found. The model proposed for two-wave mixing in the special case of a fixed Bragg angle and the constant visibility approximation improved the agreement between the theoretical results and the known experimental data. (nonlinear optical phenomena)