Polarization-based identification of bulk contributions in surface nonlinear optics

We show that bulk and surface contributions in second-order surface nonlinear optics of isotropic materials can be identified unambiguously in a single measurement by their polarization signatures. The signatures follow from the isotropy of the material and are nearly independent of its linear optical properties. Interference between the contributions allows their relative magnitudes to be quantified. For second-harmonic generation from a glass surface, the surface (bulk) contribution dominates the reflected (transmitted) signal by a factor of similar to 160 (similar to 40). The results also suggest that the inseparable, surfacelike bulk contribution can account for a significant fraction of the effective surface susceptibility of glass.