Holographic optical element based digital speckle pattern shearing interferometer

Abstract

Holographic optical element (HOE) based digital speckle pattern shearing interferometer (DSPSI) is presented. The proposed DSPSI setup consists of volume phase holographic (VPH) grating combined with ground glass (diffuser) to shear the incident wavefronts. The shear of the two wavefronts is controlled by the distance between VPH grating and the ground glass. The sheared wavefronts on the ground glass are imaged on the image detector by an imaging lens. As both interfering wavefronts are of almost equal intensities, the contrast of the digital speckle pattern shear interferometric fringes is optimum. The proposed DSPSI setup is used for the measurement of temperature and temperature distribution in butane diffusion flame under the influence of magnetic field. In DSPSI system for the measurement of temperature in gaseous flames, two speckle interferograms are recorded: one in absence of the flame and another in the presence of the flame. These two recorded speckle interferograms are subtracted to get fringe pattern corresponding to the change in refractive index. The phase information is extracted from the experimentally obtained single fringe pattern by using Riesz transform method. The obtained phase information is used to calculate the change in refractive index and hence the temperature inside the flame under study.