Spatial phase modulation from permanent memory in doped glass

Diffraction rings are observed from photoinduced permanent memory of doped glass. The permanent memory is created by the high-intensity picosecond laser beam. A 1 mm spot size of laser beam creates spatially variable refractive index memory, which appears as a void located inside the glass. When a probe laser beam passes through the memory region, the diffraction rings arisen from spatial phase modulation of the transverse phase of the input beam are created. Agreement between the observed and calculated beam pattern using Kirchhoff's diffraction integral is satisfactory.