Spectrally Isolating Rotational Raman Lines of CO2: An Experimental Demonstration of the High Resolution of Slow Light Imaging Spectroscopy

In this study, we experimentally demonstrate the high resolution of slow light imaging spectroscopy by measuring the spectrum of narrowly-spaced (93.6 GHz) rotational Raman lines of CO2 in 1 atm at room temperature. Raman spectroscopy of the gas phase is a laser diagnostic technique for measuring important parameters in aerospace applications. Results show that adjacent anti-Stokes lines of J22 and J24 can be completely isolated as no wing overlap is present. The total FWHM of Raman lines is measured to be about 18 to 20 GHz which is due to the collisional and thermal broadening of the Raman lines, the linewidth of the laser, the temporal profile of the intensifier gain, and the instrument function of the method. We characterize the combined effect of the instrument function, the laser linewidth, and the intensifier gain curve on the measurement of rotational Raman lines.