Helicity dependence of optically encoded second-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 ${\mathrm{\chi }}^{\mathrm{}\left(3\right)\mathrm{}}$(0;ω,ω,-2ω) mixing symmetries are well obeyed in semiconductor microcrystallite-doped glass but not in homogeneous silicate glasses. The radiated second-harmonic free-space mode and ${\mathrm{\chi }}^{\mathrm{}\left(2\right)\mathrm{}}$ 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.