Mid-infrared diode-laser difference-frequency spectrometer for environmental analysis

Summary form only given. Tunable single-mode laser sources in the mid-infrared (MIR) spectral range are very interesting tools for high-sensitivity and high-resolution spectroscopic identification of molecules and environmental analysis. Difference-frequency generation (DFG) in AgGaS/sub 2/ with two single mode diode-lasers gives tunable and spectrally narrow laser radiation in the spectral range between 5 and 12 /spl mu/m. For spectroscopic applications the MIR laser is used as a tunable, high-resolution light source in an absorption spectrometer. Typical absorption paths are 1<1 m but in the case of high sensitivity measurements also path lengths of up to 1=36 m can easily be realized by using multi-pass absorption cells. Besides conventional absorption cells also silver halide fibers with a diameter of 200 /spl mu/m are used as evanescent field sensors in the MIR diode-laser DFG spectrometer. This is of particular interest for on-line and in situ applications of this technique, especially when the analysis is requested in optically thick media.