<title>Diode-pumped tunable narrow-linewidth Cr:LiSAF lasers for water vapor differential absorption lidars</title>

Abstract

Diode-pumped, tunable Cr:LiSAF lasers are well suited for airborne water vapor differential absorption lidar application. Three types of diode-pumped, tunable, narrow- linewidth, injection seeded, Q-switched Cr:LiSAF lasers for high resolution atmosheric water vapor DIAL measurements in the wavelength range of 810-830 nm have been developed and investigated. By using a total internal reflection laser resonator configuration, efficient coupling of pump radiation from large diode arrays is achieved as also the ability to limit the temperature rise in the LiSAF crystal at high pump powers. The first is a high-energy Cr:LiSAF laser producing up to 25 mJ/pulse at 816 nm with a repetition rate of 1-10 Hz. A DFB diode laser locked to a water vapor absorption line using a photo-acoustic cell was employed to injection seed and tune the slave Cr:LiSAF laser. High spectral purity (<99%) and wavelength stability of 0.08 pm over a period of 10 hours were demonstrated. The second Cr:LiSAF laser is designed to operate at 100 Hz while producing up to 10 mJ/pulse with a much lesser pump power. The reduction in size and weight of this laser coupled with the increased average power leads to significant improvement in the DIAL performance over the first laser. The third diode-pumped Cr:LiSAF laser is an ultra compact laser producing up to 0.1 mJ/pulse at 1000 Hz. This laser is suitable for measuring water vapor profiles in the lower troposhere (3 to 5 km). The input-output and spectral performance of these lasers are presented.