Effect of optical activity and absorption on contradirectional two-wave interaction in Bi$_{12}$TiO$_{20}$ crystal

The dependence of relative intensity of the subject light wave on azimuths of polarization of the pump and subject waves at mutual diffraction by reflection holographic grating formed in Bi$_{12}$TiO$_{20}$ crystal is investigated. It is shown that combined effect of optical activity and absorption leads to changing of azimuths of polarization of the light waves for which maximal values of relative intensity of the subject wave are achieved. The rule of how to choose the input azimuths of polarization for achieving maximal gain of the subject wave by contradirectional two-wave interaction by reflection holographic grating in optical active crystal is established.