Frequency agile infrared lidar based on a nontracking KNbO_3 optical parametric oscillator

We present what is to our knowledge the first mid-IR lidar system based on a KNbO3 optical parametric oscillator pumped by a Ti:sapphire laser. The optical parametric oscillator works in a nontracking configuration and provides high-frequency agility from 1 to 4 µm. This system constitutes an extension to the IR of UV lidars described previously [Europhys. J. D 4, 231 (1998); Appl. Opt. 37, 2231 (1998); Atmos. Environ. 32, 2957 (1998)] for the determination of aerosol concentrations in urban atmospheres. As first field tests, measurements at 3.5 µm were performed in fog conditions. Water droplet size and concentration were determined from Mie calculations. Quantitative temporal mappings and angular profiles are presented