Studies on formation mechanisms of self-pumped phase conjugation in BaTiO_3:Ce crystals at wavelengths from 570 to 680 nm

Abstract

Formation mechanisms of self-pumped phase conjugation (SPPC) in two BaTiO3:Ce crystals with different doping concentrations have been experimentally studied. The pump beam was from dye lasers, with an overall tunable wavelength region lying between 570 and 680 nm. Variations of the optical beam path patterns as well as reflectivity of the phase conjugators with respect to the incident angle, the incident position, and the wavelength of the pump were investigated in two configurations. One configuration corresponds to that in which the pump enters an a face of the crystal; the other to that in which the pump enters the +c face of the crystal. It was found that SPPC is sometimes established in a way similar to that of a cat phase conjugator, but usually without the formation of a clear beam path loop. Sometimes SPPC is established by a stimulated photorefractive backscattering and four-wave mixing mechanism. In these cases, however, the crystal corners as well as the scattering centers on the crystal faces usually play an important role by seeding the stimulated photorefractive backscattering processes. In other cases SPPC is established by both the cat and the stimulated photorefractive backscattering and four-wave mixing mechanisms.