R. S. Sirohi

Measurement of focal length with phase-shifting Talbot interferometry

Phase-shifting interferometry with a Fourier fringe analysis technique is implemented to analyze Talbot interferometric fringes and to evaluate the focal length of a lens. A four-step algorithm is used to obtain the phase map of the lens. The slope of the phase map is related to the focal length, and it is from this relationship that we evaluate the focal length. Experimental results are presented. Our experimental study suggests that phase-shifting Talbot interferometry combined with a Fourier fringe analysis technique can be advantageously used to improve the accuracy of measurement.

Adaptive helical mirror for generation of optical phase singularity

We report a specially designed adaptive mirror that can be bent into a helical shape for generation of an optical phase singularity. The adaptive helical mirror (AHM) reported here is a reflective device that can provide a continuous phase variation of the optical field in the azimuthal direction. The construction details and evaluation of the AHM are presented. A Michelson interferometer is used for the detection of the phase singularity. The AHM can be used for generation of a singular beam having multiple topological charges, positive or negative, just by controlling the excitation voltage of the AHM.

Optical configuration for measurement in speckle interferometry.

An optical configuration for measurement of in-plane displacement and for contouring is reported. In this method an object point is viewed symmetrically with respect to surface normal and combined coherently at the image plane of the imaging system. Because the beams are combined by small apertures at the image plane, decorrelation sets in rather slowly. Owing to low decorrelation, fringes have been obtained for large in-plane deformations and large angular tilts. The method is simple to implement, and its sensitivity can be varied over a wide range. The configuration, therefore, extends the range of measurement.

Different preprocessing and wavelet transform based filtering techniques to improve Signal- to-noise ratio in DSPI fringes

Experimental results reveal that using appropriate pre-processing scheme followed by Biorthogonal wavelet filter reduced speckle index and increase the SNR significantly. This results in enhancement of contrast between dark and bright fringes. The Fig 5(d) shows that the implementation of appropriate pre-processing scheme followed by Biorthogonal wavelet filter gives more clear fringe pattern as comparison to filtering schemes results shown in Fig. 5(a), Fig. 5(b) and Fig. 5(c).