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 the residual wedge angle of a nontransparent parallel plate with a modified cyclic path optical configuration.

Abstract: A new technique for the measurement of the residual wedge angle (RWA) of a nontransparent nearly parallel plate (NPP), using a polarized He–Ne laser source, is proposed. A modified cyclic path optical configuration is used to produce counterpropagating collimated beams, which get reflected from the end surfaces of the NPP and are combined to produce two-beam Fizeau fringes, whose spacing is inversely proportional to the wedge angle of the NPP. The states of polarization of the beams reflected from the end surfaces of the NPP are transformed to opposite circular polarizations, and polarization phase shifts are applied between them. Phase shifting interferometry (PSI) has been used to determine the angular tilt between the interfering beams and, hence, the RWA of the NPP. Results obtained from a validation experiment are presented. The PSI-based technique does not suffer from any measurement ambiguities due to limitations in effective beam aperture.

Determination of the surface form error of a spherical mirror with phase shifting Sagnac interferometer.

Abstract: A polarization Sagnac interferometer (SI) is used to produce two laterally separated, identical, convergent emergent beams with linear orthogonal polarizations. The emergent p-polarized and s-polarized beams converge toward their respective focal points. The test and reference spherical mirrors are placed at confocal positions with respect to the s and p focal points so as to normally reflect back the test and reference beams through the SI that recombines the test and reference waves. Polarization phase shifting interferometry is applied to obtain the surface form error of the test surface with respect to the reference surface. A two-step measurement procedure eliminates the system aberrations. Results obtained for a concave spherical test surface with respect to a convex spherical reference surface are presented. The optical configuration is relatively less susceptible to external mechanical vibration.

Determination of the tangential surface profile of Toroidal beam line mirrors with polarization phase-shifting Twyman–Green interferometer

Abstract: A new technique for the measurement of the tangential surface profile of Toroidal mirrors (TMs) used in synchrotron radiation beam lines is proposed. A cylindrical lens placed in the collimated input (He–Ne laser) beam of a polarization Twyman–Green interferometer (TGI) forms line foci in the reference and test arms. The effect of the sagittal curvature of the TM is eliminated by adjusting a line focus on the surface of the TM, along the central tangential section. Thus, a toric test wavefront (TTW) with sagittal curvature identical to that of the incident cylindrical wavefront and tangential curvature with slope twice that of the TM, is produced along the reflection direction. The TTW interferes with a reference cylindrical wavefront, generated by retroreflecting the incident cylindrical wavefront from a reference plane mirror in the reference arm of the TGI and having identical curvature in the sagittal direction. Polarization phase-shifting interferometry has been applied to obtain the tangential surface profile of the test TM. Results are compared with other methods. The advantages of the technique are that only a plane reference mirror is needed to generate the reference beam, and the technique is suitable for TMs with long tangential radii of curvature in the kilometer regime.

Determination of surface roughness of plane optical components using quasimonochromatic light source and phase shifting interferometry

Abstract: A differential interferometric technique for the measurement of surface roughness of plane optical surfaces is proposed. A polarization Sagnac interferometer, placed in the image space of a reflection microscope system with linearly polarized, spatially coherent, quasimonochromatic incident beam illumination, splits the image-forming beam from a plane test surface (TS) into laterally sheared (LS) linear orthogonal components. The LS components interfere when brought to the same state of polarization. The optical path difference (OPD) variation along the direction of lateral shear is a measure of the slope variation on the TS. Polarization phase shifting interferometry has been applied to extract the OPD variation and thus the slope distribution, slope errors, and, subsequently, height errors. System error contribution is eliminated by combining height error data obtained for parallel sections of the TS that lie along a section of the image field parallel to the direction of lateral shear, as the TS is shifted in a direction normal to the lateral shear direction between the data capture. Results obtained for an aluminized plane polished TS are presented.

Simple technique for the accurate internal measurement of a right angle with a polarization phase-shifting, lateral-shearing, cyclic path optical configuration

Abstract: A simple, new, self-referenced technique for the internal measurement of a right angle is presented. A polarization cyclic path optical configuration (CPOC) receives as the input beam a pair of laterally separated plane wave components, having angular separation of ψw = (π±4nδ), produced due to internal reflection of a linearly polarized plane wave on the surfaces enclosing the 90-deg (±δ) angle of a right-angled prism (where δ is the error in 90-deg angle and n is the index of refraction of the material of the prism). The CPOC is used to superpose the mutually inclined plane wave components by duplicating the input pair of plane wave fronts and introducing appropriate lateral shear between the identical pairs. The superposed inclined plane wave components interfere to produce two beam Fizeau fringes (FF), when brought to the same state of polarization. The error in the right angle can be calculated simply from the spacing of the resulting FFs or, more accurately, from the slope of the optical path difference variation obtained by applying polarization phase-shifting interferometry. Results obtained for a right-angled prism are presented.

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.