Single-pulse broadband rotational coherent anti-Stokes Raman-scattering thermometry of cold N_2 gas

Coherent anti-Stokes Raman scattering (CARS) from the pure rotational Raman lines of N(2) gas is employed to measure the instantaneous (10-nsec) rotational temperature of the gas at room temperature and below. An entire rotational CARS spectrum is generated by a single laser pulse using a broad-bandwidth dye laser and is recorded on an optical multichannel analyzer. A best-fit temperature is obtained for individual experimental spectra by comparison with calculated spectra. Good agreement between CARS temperatures and thermocouple temperatures is observed.