100-kHz randomly-tuned Q-switched CO/sub 2/ laser for remote sensing

Summary form only given. LIDAR return signals from targets inherently suffer from noise caused by atmospheric variations. Increasing laser energy and improving receiver photon sensitivity enable longer-range LIDAR capability; however this type of noise is multiplicative, and thus higher laser energy will not always improve the LIDAR system performance once this kind of propagation noise becomes the dominant noise source. In the latter case the system performance can be improved by increasing the number of measurements at many different transition lines before the atmosphere changes. Considering the correlation time of atmospheric turbulence of -1 ms, as well as number of transition lines of CO/sub 2/ laser, a laser transmitter with pulse repetition and tuning rate over 50 kHz should improve the LIDAR system due to the rapid collection of data before significant environmental changes occur. For this reason, we are developing a high repetition-rate rapidly-tuned Q-switched CO/sub 2/ laser transmitter. The laser consists of an RF excited CW wave-guide gain cell and an acoustooptic tuner. The tuner consists of two acoustooptic modulators (AOMs) and a beam expander, for rapid tuning and Q-switching. Laser lines are tuned by adjusting the RF frequency to the AOMs.