Very high resolution CO laser spectrometer and first sub-Doppler line-shape studies near 60 THz (5 μm)

Abstract

laser standards. Using this technique, we can tune the CO laser frequency with absolute frequency control within the gain profile of each laser transition. The frequency uncertainty is smaller than 15 kHz, corresponding to Δν/ν=2.5×10-10. Moreover, we obtain a reduction of the CO laser linewidth by a factor of 2 down to 65 kHz, corresponding to a spectral resolution of δν/ν=1×10-9. With this outstanding accuracy and resolution we studied the shape of saturation dips in rovibrational lines of CO and carbonyl sulfide (OCS) at low pressure (<5 Pa). The self-pressure-broadening rate of CO was found to be γc=+83(7) kHz/Pa in this pressure region. This value is about four times higher than values resulting from previous measurements at much higher pressures. To our knowledge the measurements described here are the first line-shape studies with sub-Doppler resolution in the 5 μm spectral region.