RAMAN-SHIFTED LASER SOURCES SUITABLE FOR DIFFERENTIAL-ABSORPTION LIDAR MEASUREMENTS OF OZONE IN THE TROPOSPHERE

Measurements have been performed at eight laboratories on Raman-shifte d radiation from frequency-quadrupled Nd:YAG and KrF lasers. Each of t hese sources is a possible candidate for making differential-absorptio n lidar measurements of ozone in the free troposphere. The spectral pu rity, efficiency and divergence of the different sources are compared and explained using a simplified model of the Raman interaction. Parti cular attention has been given to the use of buffer gases to optimize the Raman gain and divergence. The experimental results show that the operating conditions required to optimize the output energy of each of these types of laser source can be quite different. In the case of th e KrF laser, it has been shown that high energies can be generated at low active gas pressures, and that increasing the pressure increases t he beam quality, but decreases the energy.