Phase-sensitive detection technique for surface nonlinear optics

We have developed a simple technique to measure the phase of the weak surfa ce optical second-harmonic response to excitation with femtosecond laser pu lses that uses the principle of spectral interference. This approach is nec essary for the study of surfaces under (ultrahigh) vacuum conditions, where the conventional method fails due to the dispersion in optical windows. As a demonstration, we have applied the technique to clean Ni(110) in UHV and to a Rh/Co/Cu multilayer in air. We have determined the phase with an accu racy of 5 degrees which is comparable to the conventional method. [S0163-18 29(98)50548-6].