Abstract

The pressure - temperature differential absorption lidar¹-³ utilizes two narrow band tunable pulsed alexandrite lasers. For tuning and narrow band operation, the on-line high resolution laser has three intracavity elements which are a birefringent filter, a tilt tuned thin etalon and a piezoelectrically tuned etalon. To obtain accurate temperature measurements, a line center frequency stability and accuracy of ±0.002 cm^-1 is required over an extended period of time, typically ~ 30 min, which corresponds to a set of measurements and in addition the spectral bandwidth of the on-line laser should be less than 0.02 cm^-1. A wavemeter consisting of a 5 cm coated Fizeau wedge and a Reticon detector array (with 1024 detector elements spaced at 25 μm) has been developed4 to measure the frequency and spectral line shape of the laser. Typically the output spectrum of the on-line alexandrite laser consists of three longitudinal modes which are spaced about 0.007 cm^-1 apart.

© 1990 Optical Society of America