Laser diode based new generation lidars

Recent technological advances in lasers and detectors now permit realization of relatively low cost and eye-safe lidars. Eye safety, even in the visible and near-IR regions, can be achieved by reducing laser pulse energies to a few micro-joules. The reduced signals due to such low transmitted pulse energies can be at least partially offset by operating at higher pulse repetition frequencies (PRFs). Laser diodes as lidar transmitter sources offer advantages of low cost, several available wavelengths and high PRFs, but they have also suffered from limitations of very low pulse energies, spectrally broad pulsed operation and wide beam divergence. However, the development of master oscillator-power amplifier (MOPA) laser diode configurations now offers the possibility of single-mode pulsed operation at microjoule and higher energy levels with reduced beam divergence. High efficiency photon counting avalanche photodiodes (APDs) have also become available which are capable of counting at high rates (/spl sim/20 MHz), thus permitting effective detection of micro-pulse lidar (MPL) signals. This paper addresses the design requirements of laser diode lidars, based on these technological innovations, to achieve effective aerosol and DIAL water vapor sensing.