A diode laser-diode laser-difference frequency spectrometer for the mid infrared spectral region

In the mid-infrared spectral region between 3 mu m and 25 mu m lead salt diode lasers are the most common light sources for high-resolution spectroscopy. Other light sources as CO-, CO2- lasers or sideband-lasers are expensive, non-portable and poorly tunable. To overcome the cryogenic cooling of the lead salt diode lasers and the described disadvantages of the other light sources the generation of tunable laser radiation by difference frequency generation (DFG) in non-linear crystals as an alternative method is well known. Because of the low efficiency of the non-linear process, dye, solid state or gas lasers are the preferred pump sources for difference frequency generation up to now. To use the flexibility of the non-linear process with the advantages of the visible- or near-infrared-diode lasers we developed a portable tunable cw difference frequency spectrometer applying the non-linear crystal AgGaS2 and two diode lasers as pump sources. High resolution scans over CO, N2O and OCS absorption lines near 2107 cm(-1) demonstrate the capabilities of the spectrometer. Moreover, we present high resolution line broadening measurements of the R(2) line of (CO)-C-13-O-16 in the fundamental band as well as experiments for trace gas detection of (CO)-C-12-O-16 in the fundamental band.