Theory of second-harmonic generation (SHG) in reflection from the (0001) face of hexagonal centrosymmetric (6/mmm) crystals is developed in a phenomenological approach. The bulk (electric-quadrupole) contribution to azimuthal dependences of SHG response is completely isotropic, whereas the surface (electric-dipole) contribution consists of isotropic and anisotropic parts for the 3m surface symmetry. Anisotropy entirely depends on only one component of the surface nonlinear susceptibility. This allows one to extract it directly by simultaneous measurement of the amplitude and phase of the SH wave in the (s,S) or (p,S) experimental setup. The feature is very important, if the observed anisotropy is strong and makes the surface SHG probing for these crystals completely different from the cases of cubic, rhombohedral, and tetragonal centrosymmetric crystals. In the case of weak anisotropy, the estimation of other surface components from azimuthal or polarization measurements is analyzed in detail.
© 2014 Optical Society of AmericaPDF Article