HIGHLY EFFICIENT HOLOGRAM ENHANCEMENT IN BI12TIO20 FIBER-TYPE CRYSTAL

Experimental results for two-wave mixing experiments in a single Bi12T iO20 fibre-type crystal at a wavelength of 632.8 nm under transverse a .c. electric field are reported. An exponential gain factor GAMMA = 4. 7 cm 1, which is much higher than the absorption coefficient (0.6 cm-1 ), is obtained. It is observed that the signal beam enhancement is in fact signal beam depletion for spatial frequencies higher than F(B), w hich is determined by fibre geometry. An unusually strong dependence o f response time on the recording beams intensities ratio reflects the nonlinearities of the multi-two-wave mixing process.