Advances in nonlinear optical crystals

Abstract

The building blocks available to the laser source designer for various applications such as LIDAR are continuing to progress, especially with regard to the availability of significantly improved nonlinear optical (NLO) crystals and their coatings. These crystals enhance the performance of laser systems, providing wavelength shifting and tunability with ever increasing output power across the spectral range extending from ultraviolet through the terahertz region. Progress in the development of NLO crystal growth and processing techniques at the Air Force Research Laboratory, comprising both in-house and contractual components, will be presented. The optical characteristics of many of the 'workhorse' crystals continue to improve. For example, zinc germanium phosphide (ZGP), which became the material of choice for 2-micron pumped wavelength-tunable laser sources with average powers greater than 1 watt, continues to improve in terms of transparency and laser damage threshold. In addition, the search continues for NLO crystals that may be pumped by Nd:YAG lasers and generate longer-wavelength laser output through 5 microns. Several compounds are presently being investigated including AgGaGeS₄ and AgGaGe₅Se₁₂. Related to these bulk-crystal developments, surface preparation techniques and motheye surface structures continue to be developed. Since future laser trends are toward all-fiber systems, a new effort began earlier this year on nonlinear optical fiber for super continuum generation. Finally, NLO crystals are being studied for the generation and detection of terahertz radiation. In the presentation, recent advances in the materials development will be reviewed, and the direction of future efforts in this area will be forecast.