Frequency-comb-calibrated Doppler broadening thermometry

We describe an implementation of Doppler broadening thermometry based upon a room-temperature continuous-wave quantum cascade laser at 9.07 mu m, coherently phase locked to a thulium optical frequency comb centered at 2 mu m. The thermodynamic temperature is retrieved from the analysis of multiple-line absorption spectra of the NH3 nu(2) band, adopting semiclassical line-shape models and taking into full account the speed dependence of collisional broadening. We demonstrate that a precision of approximately five parts over 10(5) can be reached as a result of the analysis of only 90 absorption spectra, as acquired as a function of the gas pressure.