Transmitter design for differential absorption water vapor LIDAR

We present a stabilized master-laser power-amplifier system for ground-based differential absorption LIDAR (DIAL) for profiling atmospheric water vapor. This system consists of two CW master lasers with the wavelength of each master laser actively stabilized. The system employs GaAlAs laser diodes for both the master lasers and the tapered laser amplifier. The on-line master laser is currently stabilized to a water vapor absorption line at 822.92 nm, using a multipass cell. The offline master laser is stabilized by locking the frequency of the beat note between the two master lasers to the peak of a 16 GHz bandpass filter for a wavelength offset of 0.036 nm from the on-line master. At the stabilized off-line wavelength water presents a negligible absorption cross section, and the two laser wavelengths have essentially identical atmospheric scattering characteristics. The tapered optical amplifier, which uses a custom designed pulsed driver, produces 1 μs pulses with peak power of ∼500 mW and a repetition rate of 3 kHz. Measurements of the spectral purity of the amplifier output, and the master lasers are presented. We next discuss the pulse timing and operation of the system and issues associated with data acquisition.