ABSTRACT
Since the 1980s, nonlinear optical methods have found useful applications in surface science. There, the problem is to optically detect and identify modifications of surfaces that are induced by physical or chemical processing. Optical methods are advantageous because they are applicable to environments that are incompatible with other techniques involving ion or electron scattering, which can only be used in ultrahigh vacuum and mostly with conducting substrates. With the great progress in controlling pulse widths, and frequency tuning of lasers, optical methods can also be used to monitor spectral resonances, very fast processes down to femtosecond timescales, and microscopic specimens.
