We describe the application of a tunable, infrared, spin-flip Raman source to the measurement of the absorption spectra of gases in the spectral region 5-6 µm. Continuous tuning was obtained by using a low finesse Raman crystal cavity to eliminate mode pulling and hopping effects. The effects of atmospheric absorption, and pulse-to-pulse and magnetic field dependent intensity variations were cancelled by using a double beam arrangement. As an illustration of the operation of such a Raman spectrometer we obtain the P and Q branch absorption spectra of nitric oxide at various gas pressures in the spectral region 1890-1835 cm-1. Studies at low gas pressure and with the tunable source operating close to the threshold for stimulated emission show a resolution of ˜ 0.08 cm-1, determined by the linewidth of the Raman scattered radiation. This linewidth is shown to be in agreement with a mechanism of stimulated superradiant narrowing of the spontaneously scattered lineshape. © 1972.
|Number of pages||5|
|Publication status||Published - Feb 1972|