Characterization of photorefractive materials by spontaneous noncolinear frequency doubling

`Spontaneous' noncolinear frequency doubling (SNCFD) is a type of optical second-harmonic generation (SHG) that uses scattered light to provide additional fundamental beams in order to accomplish noncolinear phase matching. Based on a novel algorithm for the automated evaluation of the resulting ring patterns, we present an easy-to-apply, sensitive, and non-destructive method for the characterization of photorefractive materials, yielding two-dimensional spatial resolution. As applications of the technique, examples for the characterization of lithium niobate crystals are presented.