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  • A Atlasov, Kirill, et al. (författare)
  • 1D photonic band formation and photon localization in finite-size photonic-crystal waveguides
  • 2010
  • Ingår i: OPTICS EXPRESS. - 1094-4087. ; 18:1, s. 117-122
  • Tidskriftsartikel (refereegranskat)abstract
    • A transition from discrete optical modes to 1D photonic bands is experimentally observed and numerically studied in planar photonic-crystal (PhC) L-N microcavities of length N. For increasing N the confined modes progressively acquire a well-defined momentum, eventually reconstructing the band dispersion of the corresponding waveguide. Furthermore, photon localization due to disorder is observed experimentally in the membrane PhCs using spatially resolved photoluminescence spectroscopy. Implications on single-photon sources and transfer lines based on quasi-1D PhC structures are discussed.
  • Abrahamsson, Christoffer, et al. (författare)
  • Time and wavelength resolved spectroscopy of turbid media using light continuum generated in a crystal fiber
  • 2004
  • Ingår i: Optics Express. - Optical Soc. America. - 1094-4087. ; 12:17, s. 4103-4112
  • Tidskriftsartikel (refereegranskat)abstract
    • We report a novel system for time-resolved diffuse remission spectral measurements, based on short light continuum pulses generated in an index-guided crystal fiber, and a spectrometer-equipped streak camera. The system enables spectral recordings of absorption and reduced scattering coefficients of turbid media in the wavelength range 500 - 1200 nm with a spectral resolution of 5 nm and a temporal resolution of 30 ps. The optical properties are calculated by fitting the solution of the diffusion equation to the time-dispersion curve at each wavelength. Example measurements are presented from an apple, a finger and a pharmaceutical tablet. (C) 2004 Optical Society of America.
  • Ako, Thomas, et al. (författare)
  • Design of invisibility cloaks with an open tunnel
  • 2010
  • Ingår i: Optics Express. - 1094-4087. ; 18:26, s. 27060-27066
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper we apply the methodology of transformation optics for design of a novel invisibility cloak which can possess an open tunnel. Such a cloak facilitates the insertion (retrieval) of matter into (from) the cloak's interior without significantly affecting the cloak's performance, overcoming the matter exchange bottleneck inherent to most previously proposed cloak designs. We achieve this by applying a transformation which expands a point at the origin in electromagnetic space to a finite area in physical space in a highly anisotropic manner. The invisibility performance of the proposed cloak is verified by using full-wave finite-element simulations. (C) 2010 Optical Society of America
  • Alerstam, Erik, et al. (författare)
  • Improved accuracy in time-resolved diffuse reflectance spectroscopy.
  • 2008
  • Ingår i: Optics express. - Optical Society of America. - 1094-4087. ; 16:14, s. 10440-10454
  • Tidskriftsartikel (refereegranskat)abstract
    • Significant improvements in the accuracy of time-resolved diffuse reflectance spectroscopy are reached by using a Monte Carlo scheme for evaluation of measured photon time-of-flight distributions. The use of time-resolved diffusion theory of photon migration, being the current standard scheme for data evaluation, is shown defective. In particular, the familiar problem sometimes referred to as absorption-to-scattering coupling or crosstalk, is identified as an error related to the breakdown of the diffusion approximation. These systematic errors are investigated numerically using Monte Carlo simulations, and their influence on data evaluation of experimental recordings are accurately predicted. The proposed Monte Carlo-based data evaluation avoids these errors, and can be used for routine data evaluation. The accuracy and reproducibility of both MC and diffusion modeling are investigated experimentally using the MEDPHOT set of solid tissue-simulating phantoms, and provides convincing arguments that Monte Carlo-based evaluation is crucial in important ranges of optical properties. In contrast to diffusion-based evaluation, the Monte Carlo scheme results in optical properties consistent with phantom design. Since the MEDPHOT phantoms are used for international comparisons and performance assessment, the performed characterization is carefully reported.
  • Amer, Eynas, et al. (författare)
  • UV laser interaction with a fluorescent dye solution studied using pulsed digital holography
  • 2013
  • Ingår i: Optics Express. - Optical Society of America. - 1094-4087. ; 21:21
  • Tidskriftsartikel (övrigt vetenskapligt)abstract
    • A frequency tripled Q-switched Nd-YAG laser (wavelength 355 nm, pulse duration 12 ns) has been used to pump Coumarin 153 dye solved in ethanol. Simultaneously, a frequency doubled pulse (532 nm) from the same laser is used to probe the solvent perpendicularly resulting in a gain through stimulated laser induced fluorescence (LIF) emission. The resulting gain of the probe beam is recorded using digital holography by blending it with a reference beam on the detector. Two digital holograms without and with the pump beam were recorded. Intensity maps were calculated from the recorded digital holograms and used to calculate the gain of the probe beam due to the stimulated LIF. In addition numerical data of the local temperature rise was calculated from the corresponding phase maps using Radon inversion. It was concluded that about 15% of the pump beam energy is transferred to the dye solution as heat while the rest is consumed in the radiative process. The results show that pulsed digital holography is a promisingtechnique for quantitative study of fluorescent species
  • Andersson, Mats, et al. (författare)
  • Spectroscopic studies of wood-drying processes
  • 2006
  • Ingår i: Optics Express. - Optical Society of America. - 1094-4087. ; 14:8, s. 3641-3653
  • Tidskriftsartikel (refereegranskat)abstract
    • By the use of wavelength-modulation diode laser spectroscopy, water vapor and oxygen are detected in scattering media nonintrusively, at 980 nm and 760 nm, respectively. The technique demonstrated is based on the fact that free gases have extremely sharp absorption structures in comparison with the broad features of bulk material. Water vapor and oxygen measurements have been performed during the drying process of wood. The results suggest that the demonstrated technique can give information about the drying process of wood to complement that of commercially available moisture meters. In particular, the time when all the free water has evaporated from the wood can be readily identified by a strong falloff in the water vapor signal accompanied by the reaching of a high-level plateau in the molecular oxygen signal. Furthermore, the same point is identified in the differential optical absorption signal for liquid water, with a sharp increase by an order of magnitude in the ratio of the signal intensities at 980 nm and 760 nm.
  • Antelius, Mikael, et al. (författare)
  • An apodized SOI waveguide-to-fiber surface grating coupler for single lithography silicon photonics
  • 2011
  • Ingår i: Optics Express. - 1094-4087. ; 19:4, s. 3592-3598
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the design, fabrication, and characterization of a grating for coupling between a single mode silica fiber and the TE mode in a silicon photonic waveguide on a silicon on insulator (SOI) substrate. The grating is etched completely through the silicon device layer, thus permitting the fabrication of through-etched surface coupled silicon nanophotonic circuits in a single lithography step. Furthermore, the grating is apodized to match the diffracted wave to the mode profile of the fiber. We experimentally demonstrate a coupling efficiency of 35% with a 1 dB bandwidth of 47 nm at 1536 nm on a standard SOI substrate. Furthermore, we show by simulation that with an optimized buried oxide thickness, a coupling efficiency of 72% and a 1 dB bandwidth of 38 nm at 1550 nm is achievable. This is, to our knowledge, the highest simulated coupling efficiency for single-etch TE-mode grating couplers. In particular, simulations show that apodizing a conventional periodic through-etched grating decreases the back-reflection into the waveguide from 21% to 0.1%.
  • Antosiewicz, Tomasz, 1981-, et al. (författare)
  • A simple model for the resonance shift of localized plasmons due to dielectric particle adhesion
  • 2012
  • Ingår i: Optics Express. - 1094-4087. ; 20:1, s. 524-533
  • Tidskriftsartikel (refereegranskat)abstract
    • Ultrasensitive detectors based on localized surface plasmon resonance refractive index sensing are capable of detecting very low numbers of molecules for biochemical analysis. It is well known that the sensitivity of such sensors crucially depend on the spatial distribution of the electromagnetic field around the metal surface. However, the precise connection between local field enhancement and resonance shift is seldom discussed. Using the quasistatic approximation, we developed a model that relates the sensitivity of a nanoplasmonic resonator to the local field in which the analyte is placed. The model, corroborated by finite-difference time-domain simulations, may be used to estimate the magnitude of the shift as a function of the properties of the sensed object – permittivity and volume – and its location on the surface of the resonator. It requires only a computation of the resonant field induced by the metal structure and is therefore suitable for numerical optimization of nanoplasmonic sensors.
  • Antosiewicz, Tomasz, 1981-, et al. (författare)
  • Plasmonic glasses: Optical properties of amorphous metal-dielectric composites
  • 2014
  • Ingår i: Optics Express. - 1094-4087. ; 22:2, s. 2032-2043
  • Tidskriftsartikel (refereegranskat)abstract
    • Plasmonic glasses composed of metallic inclusions in a host dielectric medium are investigated for their optical properties. Such structures characterized by short-range order can be easily fabricated using bottom-up, self-organization methods and may be utilized in a number of applications, thus, quantification of their properties is important. We show, using T-Matrix calculations of 1D, 2D, and 3D plasmonic glasses, that their plasmon resonance position oscillates as a function of the particle spacing yielding blue-and redshifts up to 0.3 eV in the visible range with respect to the single particle surface plasmon. Their properties are discussed in light of an analytical model of an average particle's polarizability that originates from a coupled dipole methodology. (C) 2014 Optical Society of America
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