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Displacement Measurement of DAST Crystal by Speckle Photography in Crystal Oscillator
Sugandhi K. and Balamurugan R.
Synthesis and the growth of 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystals by a seed rotation technique in methanol solution is described. DAST crystals have a large surface area and perform well in simple harmonic and THz generation through their peculiar characterisation. The structure and crystallinity are confirmed by the powder X-ray diffraction method. SEM analysis helps with morphological study. In the experimental setup, the optical design for displacement estimation and the crystal oscillator are simplified for convenience. A low-power coherent red laser of 650 nm by a good resolution CCD camera is employed. Speckle photography is a non-destructive method to assess the in-plane displacement on DAST crystal surfaces in the complex MEMS application field. The displacement evaluation is carried out with the help of Young’s fringes observed in the speckle pattern. The counted fringes in terms of the wavelength of the laser contribute to the displacement in the range of microns. The intensity information is obtained from the surface profile plot.
Keywords: DAST, crystal growth, SEM, Speckle photography, Young’s fringes, In-plane displacement