Molecular Velocimetry Using Photothermal Grating Induced by Laser Multibeam Interference

Abstract This paper describes the tagging velocimetry system for measuring the velocity distributions on multiline using photothermal grating. Firstly, the grating is induced by multibeam interference to make the grating image sharp. The sharp grating reduces the influence of molecular diffusion, which is inherent problem in molecular velocimetry. Secondly, the gratings of wide interval are induced by the use of diffraction gratings without and with modulation, to measure velocity in wide range. To detect the change of refractive index by the photothermal effect, we used the CCD-LD differential interferometer, which was developed in our previous study. The interferometer has functions of spatial and temporal differentiation for reducing the influence of phase fluctuations due to turbulent mixing