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 2 omega 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. (C) 1996 Optical Society of America