HELICITY DEPENDENCE OF OPTICALLY ENCODED 2ND-HARMONIC GENERATION IN GLASSES

Homogeneous silica-based and heterogeneous semiconductor-doped glasses were optically encoded with circularly polarized beams for efficient second-harmonic generation (SHG) at 532 nm. SHG growth rates for circularly polarized writing beams with both the same and opposite helicity show that chi(3)(0; omega, omega, - 2omega) mixing symmetries are well obeyed in semiconductor microcrystallite-doped glass but not in homogeneous silicate glasses. The radiated second-harmonic free-space mode and chi(2) tensor symmetries for cohelically encoded gratings in SK5 glass determined an electric field which possessed a radial component as well as a component which had a constant direction across the readout beam axis. The results are discussed in light of present theories.