Raman spectrometer for high precision temperature sensing of atmospheric gases

We present a highly accurate Raman spectrometer capable of measuring changes in atmospheric temperature as small as 0.75 K with high spatial and temporal resolution. The spectrometer is based on a laser diode tuned to the resonant absorption line of the ⁸⁵Rb isotope near 780.0 nm. A heated glass cell containing Rb atoms was used as an ultranarrowband atomic absorption notch filter with 0.3cm^-1 bandwidth and optical density as high as four. This filter was placed in front of the spectrograph and blocked up to 99.99% of the elastically scattered laser light, which made it possible to resolve the pure-rotational Raman spectra of molecular atmospheric gases. The relative intensities of pure-rotational Raman transitions were then used to infer atmospheric temperature changes.