Symmetry and phase determination of second-harmonic reflection from calcite surfaces

We perform second harmonic reflection (SHR) an the calcite surface perpendi cular to the c axis. First, we record the signal as a function of the azimu thal angle of the sample, which clearly evidences the C-3 nu symmetry of th is surface, and we show that the nonvanishing background of the p-polarized SHR is an indication of a complex-valued nonlinear susceptibility. Then, w e measure the relative phases of the susceptibility tensor components with a method that was used recently to study thin films. We vary the state of p olarization of the fundamental beam with a rotating quarter waveplate which introduces some phase difference between the different polarization compon ents. This method appears to be an easy and efficient way to measure the ph ase of SI-IR on a crystalline surface. Furthermore, comparison of both sets of experiments shows very good quantitative agreement, even though the ori gin of this phase difference is not perfectly clear. [S0163-1829(99)06504-2 ].