Development of laser spectroscopy for scattering media applications

Abstract: Laser spectroscopy for both large and small spatial scales has been developed and used in various applications ranging from remote monitoring of atmospheric mercury in Spain to investigation of oxygen contents in wood, human sinuses, fruit, and pharmaceutical solids. Historically, the lidar group in Lund has performed many differential absorption lidar (DIAL) measurements with a mobile lidar system that was first described in 1987. During the years the lidar group has focused on fluorescence imaging and mercury measurements in the troposphere. Five lidar projects are described in this thesis: fluorescence imaging measurement outside Avignon, France, a unique lidar project at a mercury mine in Almadén, Spain, a SO2 flux measurement at a paper mill in Nymölla, Sweden, and two fluorescence imaging projects related to remote monitoring of vegetation and building facades characterization. A new method to measure wind speed remotely in combination with DIAL measurements is presented in this thesis. The wind sensor technique is called videography and is based on that images of plumes are grabbed continuously and the speed is estimated by the use of image processing. A technique that makes it possible to measure a gas in solids and turbid media, non-intrusively, is presented in this thesis. The technique is called gas in scattering media absorption spectroscopy (GASMAS) and has been used since 2001. The GASMAS concept means that a traditional spectroscopy instrument, based on tunable diode lasers, is used but the gas cell or optical path is replaced by a material that strongly scatters light. Mostly, wavelength modulation spectroscopy has been utilized. Four projects using the GASMAS technique to measure gases in fruit, wood, pharmaceutical solids, and human tissue are presented. Two applications have shown a great potential so far; to be able to diagnose the health of human sinuses and gas ventilation in sinuses, and to measure gas inside pharmaceutical solids. A performance analysis of the GASMAS technique is included. This thesis also presents a technique to suppress optical noise in fiber lasers and how to construct a compact tunable diode laser spectroscopy system based on plug-in boards for a standard computer.