Frequency Comb-Based Spectroscopy of 02 for Primary Thermometry

Rovibrational absorption spectroscopy can be used for primary gas thermometry since absorption line strengths and shapes are affected by the temperature of the absorbing sample [1]. Examples of established spectroscopic thermometry techniques include Doppler-broadening thermometry (DBT), line-strength ratio thermometry (LRT), and rotational-state distribution thermometry (RDT) [1]. DBT relies on determining the temperature-dependent Doppler width of the molecular absorption line [1]. In the LR T method, the ratio of the line strengths of individual rovibrational absorption lines is determined. Due to the temperature dependency of the population in rotational states that are associated with different lines, the ratio of line strengths is temperature dependent [1]. RDT relies on this same dependency but in this method, multiple absorption line strengths over the whole absorption band are considered [2].