A POWERFUL WIDELY TUNABLE SINGLE-MODE LASER SYSTEM FOR LIDAR SOUNDING OF WATER VAPOUR THROUGHOUT THE FREE TROPOSPHERE

摘要

The high-power differential-absorption lidar system introduced at the preceding ILRC is approaching its first operation at the Schneefernerhaus high-altitude research station (2.7 km a.s.l.) on Mt. Zugspitze. Most components have been successfully tested. In this contribution we focus on a description of the results so far obtained for the laser transmitter. The single-longitudinal-mode (SLM) laser system, tunable from about 700 to 950 nm, is within its final testing phase which is in progress. The laser system consists of two SLM optical parametric oscillators (OPOs) sequentially amplified in a single Ti:sapphire ring resonator. The commercial OPOs have been significantly improved. By introducing crystal heating, modifying the pump-beam geometry, piezo tuning elements and active stabilization to a high-precision wavelength meter a satisfactory long-term performance could be demonstrated. The frequency noise was reduced to ±35 MHz, the frequency average over a few seconds is stable to within ±7 MHz. By stretching the OPO pulses to 4.0 ns a single-shot bandwidth of about 120 MHz was achieved (transform limit: 110 MHz). The amplified radiation is practically free of amplified spontaneous emission. At the submission time of this paper a pulse energy of 0.23 J was reached with reduced flashlamp power. The results suggest pulse energies of about 0.7 J under optimum conditions.