Optically encoded second-harmonic generation in bulk silica-based glasses

Lead oxid– and barium oxide–doped silicate glasses were optically encoded for efficient second-harmonic generation at 532 nm. Measurements of the tensor components of the encoded χ(2) grating and analysis of the radiated second-harmonic mode symmetries provide strong evidence that radial symmetries dominate the encoded χ(2) over most of the preparation-intensity regime. Gratings written with the highest-intensity writing beams radiated a free-space second-harmonic mode whose symmetry and tensor components were more consistent with an internal electric field that would evolve from a mixing process in an isotropic medium. Experiments were also performed to determine the dependence of the saturated χ(2) on the writing-beam intensities, the effect of UV irradiation before the encoding process, and the activation energy for thermal erasure of the gratings.