Browsing by Subject "gas thermometry"

Optical frequency combs are broadband laser light sources that produce light consisting of equally separated narrow lines. The frequencies of these comb lines can be determined and stabilized accurately. A dual-comb spectrometer is based on two optical frequency combs, and it can measure spectra at high speed and with high spectral resolution and accuracy. This requires high mutual coherence between the two combs. In this thesis, a passively coherent dual-comb spectrometer was optimized for spectroscopic temperature measurements. Spectroscopic temperature measurements presented in this thesis are based on quantifying the temperature dependence of the molecular absorption lines. In the experimental part of this thesis, three different spectroscopic temperature measurement techniques were used to measure the temperature of acetylene gas and results were compared to the temperature value of a reference temperature sensor. The three methods that are demonstrated in this thesis are line-strength ratio thermometry (LRT), rotational-states distribution thermometry (RDT), and Doppler-broadening thermometry. The measured dual-comb spectra had high quality and the dual-comb figure of merit was determined to be 5.7×10^6 Hz^(-1/2), which is a typical value for a high-quality dual-comb spectrometer. All the temperature measurements were performed at room temperature (295 K). Line-strength ratio thermometry produced the most accurate temperature results, with an estimated uncertainty of approximately 1 K. Rotational-states distribution thermometry results had an estimated uncertainty of about 3 K. Doppler-broadening thermometry did not produce reliable results, most likely due to too high gas pressure. The possible future work should be performed with larger temperature and pressure ranges to assess the accuracy of the presented spectroscopic thermometry techniques more thoroughly.