Measurement of Vibrational/Rotational Temperatures of Nitrogen in the Flow behind Strong Shock Wave by Time-resolving CARS Method

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The novel application by CARS(Coherent Anti-Stokes Raman Spectroscopy) method has been performed to the measurement of vibrational and rotational temperatures in high temperature, hypervelocity, and radiative non-equilibrium flow behind strong shock waves in low density air over the shock velocity range of 5km/sec. The system consists of YAG laser(pumping beam), dye laser(Stokes beam), optical arrangement, and II-CCD spectroscopy instrument for ultraviolet range. The CARS signal can be obtained successively both from the steady low density air and hypervelocity flow behind the strong shock wave.1.After the preliminary experiment for the steady and low density air, the spot CARS signal could be obtained from hypervelocity air behind strong shock wave of the velocity over 10km/s by using a narrow band Stokes beam of dye laser. The signal was obtained from the newly contrived trigger system and optics. Then by the broadband Stokes beam of dye laser the CARS signal that is wide enough for … More measuring the spectroscopic information of vibrational and rotational temperature has been obtained.2.Then a spectroscopic matching method is applied to the measured CARS signal with considering the parameters of optical and spectroscopic system. In the matching process the least square method is adopted in parametric shooting of vibrational and rotational temperatures. In particular non-resonant term of third-order nonlinear susceptibility is taken into account for the spectral estimation.3.From the contrived and advanced technique for the CARS measurement to our hypervelocity and radiative non-equilibrium flow, we have succeed to obtain the CARS signal data, which have enough strength and width in frequency range for the temperature decision. The vibrational and rotational temperatures have been obtained precisely by the spectroscopic matching method of measured CARS data and theoretically estimated spectroscopy for the shock velocity range over 5km/s, which is corresponding to Mach number range over 15. The precise spatial distributions of vibrational and rotational temperatures in the radiating hypervelocity flow behind the strong shock wave front have been obtained.The results have been reported in both domestic and international symposium, where strong interest and discussion have been concentrated to our novel research results. Less