Direct measurement of photoinduced charge distribution responsible for second-harmonic generation in glasses

We have found that borosilicate glasses that produce second-harmonic generation after simultaneous irradiation by fields at omega and 2omega exhibit postexposure selective etching. We use the charge specificity of the selective etching process to spatially map the photoexcited electron distributions responsible for second-harmonic generation. The results show that nearly symmetric nondipolar charge distributions exist for some regimes of encoding and that, at higher intensities, a nearly dipolar distribution is produced.