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Author

A. Krishnan

Other affiliations: Texas Tech University
Bio: A. Krishnan is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Plasmon & Surface plasmon. The author has an hindex of 10, co-authored 34 publications receiving 270 citations. Previous affiliations of A. Krishnan include Texas Tech University.

Papers
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Journal ArticleDOI
TL;DR: In this paper, a proof-of-concept imaging technique that combines the advantages of wide-field surface plasmon, leakage radiation, and total internal reflection fluorescence microscopy methods is presented.
Abstract: A proof-of-concept imaging technique that combines the advantages of wide-field surface plasmon, leakage radiation, and total internal reflection fluorescence microscopy methods is presented. High-contrast non-scanning images with subwavelength resolution of patterned and homogeneous samples coated with a fluorescent material were demonstrated. We show that the image formed in the back focal plane of the objective lens can be reconstructed from the image of the sample's surface using an algorithm similar to that used in computerized tomographic imaging. Our experimental results suggest that there is a 1-D Fourier transform relationship between any line amplitude profile at a given angle passing through the center of the sample's surface image and a line amplitude profile passing through the center of the back-focal-plane image at the same angle.

48 citations

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TL;DR: In this article, the photonic Fermi surfaces at the crystal's reciprocal lattice space can be observed directly from the Fourier plane images, where the isofrequency wavevectors of the propagating surface plasmon mode intersect the first Brillouin zone of the crystal structures.
Abstract: Light propagation in dielectric plasmonic crystals with different parameters and symmetries was investigated by plasmon tomography. We show that the photonic Fermi surfaces at the crystal’s reciprocal lattice space can be observed directly from the Fourier plane images. Directional gaps were observed where the isofrequency wavevectors of the propagating surface plasmon mode intersect the first Brillouin zone of the plasmonic crystal structures. We determined that the angular magnitude of the directional gaps depends strongly on the crystal symmetry and the lattice period.

26 citations

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TL;DR: In this paper, the propagation modes in plasmonic structures incorporating a gain medium using Fourier-plane leakage radiation microscopy were obtained with arrays of bimetallic stripes coated with a gain material.
Abstract: We report results on the propagation modes in plasmonic structures incorporating a gain medium using Fourier-plane leakage radiation microscopy. We demonstrate that high contrast images and detailed mode propagation information can be obtained with arrays of dielectric loaded surface plasmon waveguides. Clear interference effects were observed in the Fourier-plane images corresponding to arrays of bimetallic stripes coated with a gain material. This indicates coherent superposition of leaked fluorescence from coupled adjacent waveguides as a result of plasmon stimulated emission.

22 citations

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TL;DR: In this article, a linear polarizer in the optical path of the light within a leakage-based microscope was used to identify the polarization states of SPP modes excited in plasmonic waveguides.

21 citations

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TL;DR: In this paper, a dynamic direct space-to-time pulse shaper based on the combination of a reflective arrayed waveguide grating multiplexer and an array of digital micromirrors used as an external reflector was described.
Abstract: We describe a dynamic direct space-to-time pulse shaper based on the combination of a reflective arrayed waveguide grating multiplexer and an array of digital micromirrors used as an external reflector. Spatial modulation was obtained by imposing a reconfigurable periodic structure on the digital micromirror array. The period of this structure and the number of reflecting micromirrors within each period was varied to produce pulse sequences with variable repetition rates within the burst and different pulsewidths. Experimental results are in excellent agreement with simulated temporal output response.

20 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the compensation of loss and amplification of surface plasmons in waveguides and resonators is discussed, and future challenges, including how to overcome the large losses present in plasmonic systems that offer strong electromagnetic confinement, are also discussed.
Abstract: This Review provides an introduction to the compensation of loss and amplification of surface plasmons in waveguides and resonators. Future challenges, including how to overcome the large losses present in plasmonic systems that offer strong electromagnetic confinement, are also discussed.

703 citations

Journal Article
TL;DR: In this article, the existence of efficient exciton-exciton annihilation, a four-body interaction, in monolayer MoS2 was identified experimentally in ultrafast transient absorption measurements through the emergence of a decay channel varying quadratically with exciton density.
Abstract: Monolayer MoS2 is a direct-gap two-dimensional semiconductor that exhibits strong electron-hole interactions, leading to the formation of stable excitons and trions. Here we report the existence of efficient exciton-exciton annihilation, a four-body interaction, in this material. Exciton-exciton annihilation was identified experimentally in ultrafast transient absorption measurements through the emergence of a decay channel varying quadratically with exciton density. The rate of exciton-exciton annihilation was determined to be (4.3 ± 1.1) × 10(-2) cm(2)/s at room temperature.

292 citations

01 Jan 1997
TL;DR: In this paper, a femtosecond code-division multiple access (CDMA) communication system test bed operating over optical fiber in the 1.5 /spl mu/m communication band is presented.
Abstract: This paper reports comprehensive experimental results on a femtosecond code-division multiple-access (CDMA) communication system test bed operating over optical fiber in the 1.5 /spl mu/m communication band. Our test bed integrates together several novel subsystems, including low-loss fiber-pigtailed pulse shapers for encoding-decoding, use of dispersion equalizing fibers in dispersion compensated links for femtosecond pulse transmission and also in femtosecond chirped pulse amplification (CPA) erbium doped fiber amplifiers (EDFAs), and high-contrast nonlinear fiber-optic thresholders. The individual subsystems are described, and single-user system level experimental results demonstrating the ability to transmit spectrally encoded femtosecond pulses over a 2.5-km dispersion compensated fiber link followed by decoding and high contrast nonlinear thresholding are presented.

176 citations

Journal Article
TL;DR: A novel gold coated femtosecond laser nanostructured sapphire surface based on surface-enhanced Raman spectroscopy (SERS) for detecting vapours of explosive substances was investigated and demonstrates a simple sensing system that is compatible with commercial manufacturing practices to detect taggants in explosives.
Abstract: A novel gold coated femtosecond laser nanostructured sapphire surface - an “optical nose” - based on surface-enhanced Raman spectroscopy (SERS) for detecting vapours of explosive substances was investigated. Four different nitroaromatic vapours at room temperature were tested. Sensor responses were unambiguous and showed response in the range of 0.05-15 µM at 25 °C. The laser fabricated substrate nanostructures produced up to an eight-fold increase in Raman signal over that observed on the unstructured portions of the substrate. This work demonstrates a simple sensing system that is compatible with commercial manufacturing practices to detect taggants in explosives which can undertake as part of an integrated security or investigative mission.

110 citations

Journal ArticleDOI
TL;DR: In this article, the authors provide an updated vision of the types of RLs and RFLs that have been demonstrated and reported, from dyes solutions embedded with nano/submicron-scatterers composites to rare-earth doped micro or nanocrystals and random fiber Bragg gratings as the scattering structure.

80 citations