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

CARS（相干反斯托克斯拉曼光谱）方法的新应用已被用于在5km/秒激波速度范围内的低密度空气中强激波后的高温、超高速和辐射非平衡流中的振动和旋转温度的测量。该系统由YAG激光器（抽运光束）、染料激光器（斯托克斯光束）、光学装置和II-CCD紫外光谱仪组成。在强激波后的稳定低密度空气和超高速气流中均可依次获得CARS信号。经过对稳定低密度空气的初步实验，利用染料激光窄带Stokes光束可以在速度大于10km/s的强激波后的超高速空气中获得点CARS信号。信号由新设计的触发系统和光学器件获得。然后利用染料激光的宽带斯托克斯光束获得了足够宽的CARS信号，进一步测量了振动和旋转温度的光谱信息。在此基础上，结合光学系统和光谱系统的参数，对实测CARS信号进行光谱匹配。在匹配过程中，采用最小二乘法对振动温度和旋转温度进行参数化射击。特别是考虑了非共振项的三阶非线性磁化率进行谱估计。从人为的先进的CARS测量技术到我们的超高速和辐射非平衡流，我们成功地获得了CARS信号数据，这些数据在频率范围内具有足够的强度和宽度来确定温度。在激波速度大于5km/s的范围内，即马赫数大于15的范围内，通过实测CARS数据与理论估计光谱的光谱匹配方法，精确地获得了振动温度和旋转温度。得到了辐射超高速流在强激波锋后的振动温度和旋转温度的精确空间分布。研究成果已在国内外学术会议上发表，并引起了广泛的关注和讨论。少

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