Mining the polarization-dependence of nonlinear optical measurements.

The electromagnetic field strength present within the focal volume of a pulsed laser is routinely high enough to produce reasonably efficient nonlinear summing and mixing of optical frequencies. The polarization-dependence of the outgoing beam is a sensitive function of the polarization state(s) of the incident beam(s) and the structure, orientation, and symmetry of the sample. Mining this information hinges on two elements: (1) accurate and precise polarization-dependent measurements, and (2) reliable modeling to relate the measured responses back to local structure and orientation. The central focus of this review is on the first step. Experimental strategies for precise and accurate nonlinear optical ellipsometry (NOE) polarization measurements are summarized for the most common and simplest case of second harmonic generation (SHG), or the frequency doubling of light, although extension to higher-order nonlinear optical interactions is straightforward in most cases.