We report the design and performance of a tunable, pulsed high resolution mid infrared cavity ringdown spectrometer. Stimulated Raman scattering in H-2/D-2 is used to downconvert the output of a SLM Alexandrite ring laser (720-800 nm) to the mid infrared (3-8 mum). The infrared frequency bandwidth was determined to be 90+/-5 MHz from measurements of Doppler broadened OCS transitions at 5 mum. The minimum detectable per pass fractional absorption is 1 ppm. We observe a frequency dependent ringdown cavity transmission of +/-5 ppm due to spatial variations of the mirror reflectivity. The upsilon(6) band of linear C-9 formed by laser ablation of graphite in a He molecular beam was measured, showing a factor of 2 improvement in sensitivity relative to previous IR diode laser experiments. Based on calculated IR intensities, the number density of C-9 in the molecular beam is 1.3(*)10(11) molec/cm(3) and the minimum detectable density is 1(*)10(9) molec/cm(3). We expect this spectrometer to be a powerful tool for the study of transient species formed in molecular beams. (C) 2002 American Institute of Physics. [References: 30]
展开▼
