High gain nondegenerate two-wave mixing in Cr:YAlO3

Recently we demonstrated a gain of 6 times that was obtained by nondegenerate two-wave mixing in Cr:YAlO₃. Here we report new experiments in which a gain of 22 times was achieved by increasing both the interaction length and the doping of the material. To our knowledge, this is the largest cw two-wave mixing gain obtained in a bulk, solid state, nonphotorefractive material. Experiments demonstrating high gain, nondegenerate two-wave mixing in new solids using low power cw lasers constitute an essential step in establishing the viability of alternative materials for applications of nonlinear optics in areas such as signal processing. Availability of high gain can bring about rapid progress in experimental research, as occurred with the discovery of photorefractive materials such as barium titanate. To our knowledge however, no one has demonstrated gain comparable to that of photorefractive materials by using a solid state bulk (as opposed to guided wave) Kerr medium with a cw source. We report properties of a candidate material, chromium-doped yttrium aluminate (Cr:YAlO₃), that may significantly advance experimental efforts on nonlinear optics in Kerr-like media, much the way basic studies of barium titanate initiated widespread study of nonlinear optics in photorefractive materials. Motivation for the present work was provided by the expectation of new properties that should result from the different nonlinear mechanism (Kerr-like vs. photorefractive), such as improved dynamic range in mutually pumped phase conjugation that is important in wavefront matched heterodyne receivers