New technology for compact, eye safe lidar is surveyed. Advances with solid state lasers and detectors permit efficient lidar designs that meet requirements for full time atmospheric monitoring. Micro pulse lidar is an approach that employs kHz pulse rate Nd:YLF lasers and micro Joule pulse energies at visible wavelengths. Eye safety is an essential factor and is obtained by beam expansion. High performance is realized by solid state Geiger mode avalanche photodiode photon counting signal acquisition. The capability to monitor all significant cloud and aerosol scattering by a compact instrument has been demonstrated. Pseudorandom modulation CW lidar is under development. CW diode lasers are used directly as transmitters with the advantage of wavelength tunability for water vapor and other differential absorption measurements. Background photon noise and dynamic range are problems for CW lidar. Advanced conventional pulsed diode laser lidar and near infrared lidar at fundamentally eye safe wavelengths are in development for some applications.

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The phase-front quality of the primary spatial lobe emitted from an injection-locked gain-guided AlGaAs laser diode array is measured by using an equal-path, phase-shifting Mach-Zehnder interferometer. Root-mean-square phase errors of 0.037 +/- 0.003 wave (lambda/27) are measured for the single spatial lobe, which contained 240-mW cw output power in a single longitudinal mode. This phase-front quality corresponds to a Strehl ratio of S = 0.947, which results in a 0.23-dB power loss from the single lobe's ideal diffraction-limited power. These values are comparable with those measured for single-stripe index-guided AlGaAs lasers.

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