Diode laser injection seeding of a pulsed Ti:sapphire laser for remote sensing

High pulse energy (100–150 mJ) high spectral purity (>99.7%) injection seeding is reported for a pulsed unstable resonator Ti:sapphire laser using a cw single-mode 100-mW diode laser in the 820-nm region. The laser characteristics meet the strict requirements of a NASA Lidar Atmospheric Sensing Experiment mission in differential absorption lidar (DIAL) remote sensing of water vapor. Long and short term laser frequency stability is obtained by locking the diode laser frequency to an absorption line of water vapor in a reference cell using a frequency modulation technique. Operation on and off the water vapor absorption lines for the DIAL measurements is achieved by applying current pulses to the diode laser, which greatly simplifies the DIAL system. The spectral purity of laser output is measured using two White cells with a total path length of 400 m. Diode laser side mode seeding was found to be the major limitation to higher spectral purity. By suppressing the diode laser side mode with a solid etalon, spectral purity higher than 99.7% has been obtained.