Y. Pavan Kumar

Bio: Y. Pavan Kumar is an academic researcher from Raja Ramanna Centre for Advanced Technology. The author has contributed to research in topics: Interferometry & Wavefront. The author has an hindex of 8, co-authored 38 publications receiving 199 citations.

Measurement of centering error of a lens with cyclic optical configuration

Abstract: A new technique for the measurement of centering error (CE) of a lens using a cyclic path optical configuration (CPOC) is presented. The test lens (TL) is placed in the CPOC, adjusted for zero lateral shear. The mechanical axis (MA) of the TL holder is prealigned along the direction of the central ray (CR) of the counterpropagating collimated beams of the CPOC. A pencil beam is also set along the CR outside the CPOC. If the TL is free from CE, then its optical axis (OA) would coincide with the MA and the CR. The focal points F1 and F2, formed by the TL, and the center of the Haidinger-type fringes, due to interference of the light from F1 and F2 (which is along the line joining F1 and F2), would also lie on the CR. In the presence of CE, F1 and F2 would be laterally displaced from the CR and the fringe center (FC) suffers a deviation from the CR. Adjustments in the angular and lateral positions of the TL necessary to align the OA along the CR, as can be ensured from the coincidence of the FC with the CR, give a measure of the CE.

Measurement of the surface profile of a curved optical surface with rotation phase-shifting lateral shear cyclic path optical configuration.

Abstract: We present a new (to our knowledge) technique for introducing phase shifts between the laterally sheared emergent beam components of a cyclic path optical configuration (CPOC). The phase shifts are introduced by applying a small change in the angle of incidence of the incident beam due to the small angular rotation of the CPOC setup. Phase-shifting interferometry has been applied along with this phase-shifting technique for a CPOC with lateral shear to find the surface slope/profile of curved optical surfaces. Results for a spherical optical surface have been discussed. An optical setup for measurement of the surface profile of toroidal beam line mirrors of synchrotron radiation sources is proposed.

Application of Newton's method to determine the focal length of lenses using a lateral shearing interferometer and cyclic path optical configuration setup

Abstract: We present a technique for the focal length measurement of lenses applying Newton's method, using a cyclic path optical configuration (CPOC) and a wedge shear plate (WSP). Two point sources of orthogonal linearly polarized light waves that have a known longitudinal separation between them are generated using CPOC. Selecting a particular state of polarization (s or p), the corresponding point source is made to coincide with the back focal point of the test lens (TL). The collimation of the output beam from TL is tested using the WSP. With a change in the state of polarization, a spherical wavefront would emerge from TL because the corresponding point source is situated slightly away from the focal plane of TL. The radius of curvature of the emerging spherical wavefront from TL approximated as image distance is evaluated by analyzing the shear fringes produced by WSP. Appropriate formulae for the determination of the focal length of TL, from the image distance and known longitudinal separation between the sources, are derived using Newton's method. Results obtained for a positive doublet lens of nominal focal length of 500.0 mm is presented.

Simple technique for the generation of white light Young's fringes with a cyclic optical configuration

Abstract: A new (to our knowledge) technique for the generation of white light Young's type fringes using a cyclic path optical configuration is presented. The effect of the size of an incoherent broadband light source on the fringe visibility is discussed. Applications and advantages of the technique are described.

Measurement of longitudinal displacement using lateral shearing cyclic path optical configuration setup and phase shifting interferometry

Abstract: We present a technique for the measurement of longitudinal displacement using a lateral shearing cyclic path optical configuration (CPOC) setup and phase shifting interferometry. In the technique, a plane mirror mounted on a linear translation stage, placed slightly away from the focal plane of a lens, introduces a longitudinal focal shift to the incident focusing beam. The resulting spherical wavefront emerging from the lens is sheared into two orthogonally polarized beams using the CPOC setup. By applying polarization phase shifting interferometry (PPSI), the longitudinal focal shift of the beam focus is calculated by determining the slope of the optical path difference variation between the sheared beams. Similarly, the additional focal shift introduced due to longitudinal translation of the mirror, by an unknown amount, is determined using PPSI. Half of the difference between the two longitudinal focal shifts measured gives the longitudinal displacement of the mirror. The technique can be used for an extended range of distance measurement. The novelty of the technique is the introduction of CPOC for the distance measurement. The advantages of the technique compared to other related methods are discussed.

Young`s interference experiment with light scattered from two atoms

Abstract: We report the first observation of interference in the light scattered from two trapped atoms ({sup 198}Hg{sup +} ions localized in a linear Paul trap). The visibility of the interference fringes can be explained in the frame-work of Bragg scattering by a harmonic crystal, but with important differences compared to the case of a large crystal. Comparison of the experimental data with theory shows that the interference pattern offers another method to determine ion temperatures and separations. Furthermore, by exploiting the atom`s internal structure we have found a way to obtain {open_quotes}which path{close_quotes} information without invoking the position-momentum uncertainty relation. If the light scattered by the atoms is detected in a polarization-sensitive way, then it is possible to selectively demonstrate either the particle-nature or the wave-nature of the scattered photons.

Characterization of Bessel beams generated by polymeric microaxicons

Abstract: We present a quick, simple and accurate digital holographic characterization of the Bessel beams produced by polymeric microaxicons. This technique allows the numerical reconstruction of both intensity and phase of the beam at whichever point starting from a single acquired hologram. From these data, it is possible to go back to the axicon structure, and to gather information about their characteristics. In particular, the focal length and the depth of focus of the axicon lens are experimentally measured, and the full width at half maximum of the beam is obtained too. The depth of focus, very large for a Bessel beam with respect to a Gaussian one, is successfully exploited for optical trapping of micrometric objects.

Development of a compact, fiber-coupled, six degree-of-freedom measurement system for precision linear stage metrology

Abstract: A compact, fiber-coupled, six degree-of-freedom measurement system which enables fast, accurate calibration, and error mapping of precision linear stages is presented. The novel design has the advantages of simplicity, compactness, and relatively low cost. This proposed sensor can simultaneously measure displacement, two straightness errors, and changes in pitch, yaw, and roll using a single optical beam traveling between the measurement system and a small target. The optical configuration of the system and the working principle for all degrees-of-freedom are presented along with the influence and compensation of crosstalk motions in roll and straightness measurements. Several comparison experiments are conducted to investigate the feasibility and performance of the proposed system in each degree-of-freedom independently. Comparison experiments to a commercial interferometer demonstrate error standard deviations of 0.33 μm in straightness, 0.14 μrad in pitch, 0.44 μradin yaw, and 45.8 μrad in roll.

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.

A simple technique for measuring thickness distribution of transparent plates from a single image by using the sampling moiré method

Abstract: A simple measurement technique for the thickness distribution of transparent plates is proposed by using the sampling moire method. The thickness distribution is automatically analyzed by measuring the phase difference of the moire fringe obtained from a single image, consistent with light refraction. The relationship between the actual thickness and phase difference of the moire fringe is calibrated by using glass plates of known thicknesses. The thickness measured by the present method was found to be in agreement with measurements using a digital micrometer. In our experiment, the average error in glass plate thickness was 1.9% over a 3.5 mm measurement range. Experimental results indicate that the present method can be useful for nondestructive measurements of the thickness distribution of various transparent plates.