Interface imaging by second-harmonic microscopy

Second-harmonic microscopy (SHM) is a fast noncontact surface specific imaging technique for the quantitative in situ characterization of a large variety of real interfaces including liquid surfaces, surfaces in vacuum, and buried interfaces. The conventional surface second-harmonic generation experiment reveals the surface order and symmetry averaged over the area illuminated with an intense laser beam. In contrast, the SHM experiment probes the interface laterally resolved. Here we show that the optical nonlinearity of any local feature resolved in an image can be measured quantitatively. The nonlinear optical properties can be interpreted in terms of local surface order and symmetry. The lateral resolution limit of the stigmatic microscope is Abbe's resolution for the generated SH light with a wavelength of, e.g., 532 nm. The contrast mechanism can also be applied to a scanning optical near field microscope. (C) 1997 American Vacuum Society. [S0734-211X(97)04304-7].