Sarvendra Singh Negi

Bio: Sarvendra Singh Negi is an academic researcher from Raja Ramanna Centre for Advanced Technology. The author has contributed to research in topics: Phase (waves) & Interferometry. The author has an hindex of 2, co-authored 2 publications receiving 18 citations.

Small roll angle measurement using lateral shearing cyclic path polarization interferometry.

Abstract: We present a technique for the measurement of roll angular displacement of a rotary stage using a lateral shearing cyclic path optical configuration (CPOC) setup and polarization phase shifting interferometry (PPSI). The CPOC setup, aligned on the rotary stage, laterally shears the input plane polarized spherical beam into a pair of orthogonally polarized beams, which when brought to the same state of polarization by a polarizer produce interference fringes similar to Young's fringes. Rotation of the CPOC setup in its plane introduces a phase change between the orthogonally polarized lateral sheared beams due to the change in angle of incidence of the input beam. The change in the phase results in spatial displacement of the interference fringes. Using PPSI, the phase, or the optical path difference change between the laterally sheared beams that is related to the rotation angle of the CPOC setup, is measured.

Measurement of surface form error of an optical surface with reduced interferometric spatial coherence artifacts using a ring source and polarization phase-shifting interferometry.

Abstract: We present a technique for the measurement of surface form error of an optical surface using a ring source and polarization phase-shifting interferometry (PPSI). The ring source, generated using a refracting axicon, is projected onto a rotating diffuser to reduce the spatial coherence noise generated by the spatially coherent He-Ne laser and to enhance the interference fringe contrast. PPSI is applied to extract the phase [and hence the optical path difference (OPD)] from the interference fringes formed by a Fizeau cavity using the ring source. The OPD values are least-square fitted to a plane and the surface form errors are evaluated from the deviations of the OPD values from the fitted reference plane. A two-step subtraction method to reduce the system errors and the effect of the ring source diameter on the effective measurement area of the test surface are discussed. The main advantage of the technique is that the perturbations in the Fizeau cavity are negligible during the phase shifts as the phase shifts between the interfering beams are introduced outside the cavity.

A ring-shaped random laser in momentum space.

Abstract: A ring-shaped random laser in momentum space is designed by directly coupling a random laser with a commercial optical fiber. By using a simple approach of selectively coating the random gain layer on the surface of the fiber, red and yellow random lasers are respectively achieved with low threshold values and a good emission direction due to the guiding role of optical fibers. The unique coupling mechanism leads to a random laser with a ring shape in momentum space, which is an excellent illuminating source for high-quality imaging with an extremely low speckle noise. More importantly, a triple-state color-switchable random laser with yellow, red and yellow-red dual-colors can be flexible, and is obtained by simply moving the pump position. The results may promote the practical applications of random lasers in the fields of sensing, in vivo biological imaging, and high brightness full-field illumination.

Precision roll angle measurement based on digital speckle pattern interferometry

Abstract: An approach to precise measurement of small roll angle based on digital speckle pattern interferometry (DSPI) is introduced. A simple relationship between the roll angle and interferometric phase distribution is established by analyzing the mechanism of fringe formation in the process of roll detection using a dual-beam DSPI, and reasonable approximate processing. The presented method enjoys some important advantages, such as being free of a cooperative target and a very high measurement resolution. In our experiments, a measurement resolution of 1 µrad, which can compete with the best resolution of the existing methods, is achieved. Theoretically, the measurement resolution can even be improved to tens of nano-radians at the cost of increasing the size of the measuring device. The performance of the method is also demonstrated by a comparison experiment.

Double-grating with multiple diffractions enabled small angle measurement.

Abstract: We demonstrate a small angle measurement setup enabled by the double-grating configuration, where the multiple diffractions are used to magnify the deflection angle of the optical beam. Such small angle measurement setup has characteristics of high sensitivity and compact size. The use of two unparallel blazed gratings with a special included angle can realize multiple diffractions for the incident light, leading to the realization of deflection angle amplification. Experimental results verify that small angle can be accurately characterized and the angular resolution of measurement can be improved more than 40 times by inserting the double-grating configuration into the conventional auto-collimation angle measurement setup. Therefore, the micro-radian angle can be accurately measured with our proposed compact characterization setup.

Nanoscale tilt measurement using a cyclic interferometer with polarization phase stepping and multiple reflections.

Abstract: High-accuracy tilt or roll angle measurement is required for a variety of engineering and scientific applications. A cyclic interferometer with multiple reflections has been developed to measure small tilt angles. To accomplish this task, a novel and simple method, phase shift by polarization, was developed. The results of these studies show that the multiple reflection cyclic interferometers can be used to measure object tilts on the order of 0.2 nano-radians. We develop the theory for polarization phase step and show that accurate measurements can be made with the cyclic interferometer.