Choice of optimal conditions for light diffraction and two-wave interaction in a cubic photorefractive piezoelectric $Bi_{12}SiO_{20}$ crystal

The maximum and minimum diffraction efficiencies and the effective amplification of a hologram are studied experimentally in a 2.1 mm thick, ($\bar1\bar10$) cut $Bi_{12}SiO_{20}$ crystal as functions of the orientation angle formed by the vector of a holographic grating with the crystallographic direction $[001]$. A comparison is made between the orientation dependences of the polarisation azimuths at which the extrema of the diffraction efficiency and of the effective amplification are achieved. It is shown that the polarisation azimuths of the reading light corresponding to the maximum diffraction efficiency and the maximum effective amplification coincide within the orientation angles $0-90^\circ$ and $270-360^\circ$ and differ by $90^\circ$ in the range $90-270^\circ$.