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 (720-800nm)to the mid infrared (3-8#mu#m).The infrared frequency bandwidth was determined to be 90+-5MHz from measurements of Doppler broadened OCS transitions at 5#mu#m.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 v_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.Bsed on calculated IR intensities,the number density of C_9 in the molecular besm is 1.3~*10~(11) molec/cm~3 and the minimum detertable density is 1~*10~9molec/cm~3.We expect this spectrometer to be a powerful tool for the study of transient species formed in molecular beams.
展开▼
