Measurement of Rotational Temperature in a Molecular Beam with Femtosecond Laser Pulses

We apply high-order harmonic generation to sensitive measurements of molecular rotational temperature in a thin supersonic gas beam. The method uses nonresonant pump and probe femtosecond laser pulses to generate the harmonic radiation from coherently rotating molecules. The rotational temperature of molecules can accurately be derived with high spatial and temporal resolutions from the Fourier spectrum of time-dependent signals. The validity of method was tested for an expanding flow of N2 beam with a rapid temperature decrease. The results show the versatile applicability of this method.