Observation of solid surfaces by an optical second harmonic microscope

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Optical second harmonic generation (SHG) has a useful feature as a surface probe : high sensitivity to the symmetry at surfaces. We have developed a SH microscope as a new surface probe with excellent spatial resolution and have carried out various studies on surface physics using the SH microscope.(1) The developed SHG microscope system has high sensitivity and high signal to nose (S/N) ratio enough to detect the weak surface SH light. The spatial resolution of the developed SH microscope is about 1mum.(2) We have observed SH intensity images of cleaved GaAs(110) surfaces in order to demonstrate that the SHG microscope is powerful in observing small structures (steps and holes) with the size of a few micrometers on surfaces. Especially we have discovered an interesting phenomenon : The SH intensity from slab structures was enormously enhanced due to the interference of multi-reflected incident light.(3) We have obtained SH intensity images of metal grating surface with the SH microscope, for the first tome. The SH images had a feature of a stripe pattern, and the SH intensity at the bottom of the grooves was much higher than that on the tops of the grooves. The result indicates that the electric field at the bottom of the groove is enhanced and intensifies the SH response.