Optical amplification of photoinduced polarizability gratings in phosphate glasses

It is experimentally demonstrated that second-order polarizability gratings preliminarily recorded using bichromatic light in a phosphate glass can be amplified under the action of monochromatic radiation. The amplification effect takes place irrespective of the polarization and direction of propagation of the amplifying radiation and is achieved at various wavelengths. The phenomenon is related to the asymmetry of optical transitions between local centers in an isotropic medium in the presence of electric field. It is theoretically shown that this system may feature the formation of alternating electric field domains with dimensions depending on the grating amplitude.