Tunable, Narrow Linewidth, High Repetition Frequency Ce:LiCAF Lasers Pumped by the Fourth Harmonic of a Diode-Pumped Nd:YLF Laser for Ozone DIAL Measurements

Abstract

Ozone plays a crucially important role in all aspects of human life, although it is only a trace gas present in the middle and low atmosphere. Variations in ozone concentration in the stratosphere have an affect on the protection of the earth’s biosphere from the harmful portion of the Sun’s ultraviolet rays. Tropospheric ozone initiates the formation of photochemical smog and in high concentrations is harmful to human health and vegetation. Also ozone has a significant influence on the earth radiation budget. Human activities have produced adverse effects on atmospheric ozone distribution, which it left unchecked could lead to catastrophic changes to the biosphere . Hence the continuous measurement of ozone with good spatial resolution over large regions of the globe is an important scientific goal. A remote sensing technique for the monitoring of ozone concentration based on differential absorption lidar (DIAL) has been established as a method providing rapid and precise time and spatial resolutions [Browell, 1989, Richter, 1997]. Ozone absorbs strongly in the UV over the 240 – 340 nm region and also in the IR at near 9.6 μm. A two-wavelength differential absorption technique in the UV is commonly used for ozone measurement. After obtaining the lidar signals at two neighboring wavelengths (onand off-line), the differential absorption due to ozone is obtained by taking the ratio of the two signals to eliminate the contribution to extinction from scattering commen to both signales. Since the ozone absorption in UV exhibits a smooth band structure, the separation between the onand offline wavelengths is required to be a few nanometers. A number of ground-based [Profitt & Langford, 1997] and aircraft-based DIAL [Richter et al.,1997] systems for monitoring ozone concentrations in the planetary boundary layer, the free troposphere and the stratosphere have been developed by research groups all over the world [McGee et al, 1995, Mc Dermit et al,1995, Carswell et al,1991, Sunesson, et al,1994]. Most of the ground-based ozone DIAL instruments utilize large excimer gas lasers and Raman wavelength shifters, or flashlamp pumped frequency tripled and quadrupled Nd:YAG lasers and dye lasers, which are large complex systems requiring considerable