9860955<br/> This Small Business Innovation Research (SBIR) Phase I project addresses the need for reliable, low cost, high resolution monitoring of atmospheric water vapor. A 50-microjoule per pulse, 10-kilohertz optical parametric oscillator (OPO) will be investigated to profile water vapor using the differential absorption lidar (DIAL) technique. This OPO, pumped with 532-nanometer (nm) radiation, will use a new nonlinear material - periodically poled lithium tantalum oxide (PPLT). PPLT is used because of its high transparency in the ultraviolet . This is thought to be the first investigation of 532 nm and 355 nm pumping of PPLT OPOs. Photorefractive effects on OPO performance and beam quality will be measured at 532 nm and 355 nm for crystal operating temperatures between 100 and 350 degrees Celsius. The result of this research is expected to be an experimentally verified DIAL transmitter design.<br/> Commercial applications of this research include molecular imaging and optical biopsies. High repetition rate, low-pulse energy lasers operating between 400 and 700 nm (achieved by pumping a PPLT OPO with 355 nm) are needed as excitation sources for fluorophores, in molecular imaging, and for fluorescence return signatures, in optical biopsies. High volume production for these commercial markets is expected to lower the per unit cost of DIAL transmitters significantly.