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.

Interferometric-auto-collimation technique for the determination of small angular tilt of a plane mirror

Abstract: A new common path interferometric auto-collimation technique is proposed. A laser autocollimator is combined with a modified triangular path interferometer for generating Fizeau fringes formed due to interference between two split up plane wave components with angular separation equal to four times of the angular deflection of the plane test mirror. The angular deflection of the plane test mirror is measured either from the fringe spacing or more accurately, from the slope of the optical path difference variation of the interference field obtained by applying polarization phase shifting interferometry. Results for a validation experiment are presented.

Un-polarized light transmission DIC microscope

Abstract: A new technique for creating Differential Interference Contrast (DIC) images of transparent specimens, using un-polarized, white light is discussed. A Sagnac interferometer (SI) is used in the image space of a transmission DIC microscope to produce small/differential laterally sheared, coherent beam components that interfere to form DIC images. Phase shifts between the exit beam components are introduced by applying small angular rotation of the SI in its own plane. Results obtained for a transparent watermark on a glass slide are presented. Most important advantage of the technique is that the birefringence of a test specimen does not affect the DIC images as un-polarized light is used.

Simple technique for fabrication of Nd-phosphate laser glass rods for high power lasers

Abstract: A technique for fabrication of Nd-glass laser rods from raw laser glass slab is presented. Cylindrical laser glass rods are prepared by using custom made glass sawing, milling and edging machines. A square section bar of laser glass, which is sawn from the slab, is converted to that with octagonal section by flat milling of the four corners of the square section bar. The rod with octagonal section is then transformed to a rod with right circular section in a glass edging machine. A ball-bearing based setup, which can be attached to the oscillatory arm of a conventional polishing machine, for simultaneous polishing of the flat end faces of a number of laser rods fixed in holders, is described. The method is suitable for fabrication of both large and small diameter laser rods.

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.