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Sökning: L773:1094 4087

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31.
  • Arias, Augusto, et al. (författare)
  • Simultaneous rotation, orientation and displacement control of birefringent microparticles in holographic optical tweezers
  • 2013
  • Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 21:1, s. 102-111
  • Tidskriftsartikel (refereegranskat)abstract
    • We report the experimental implementation of a new method for generating multiple dynamical optical tweezers, where each one of them is generated with an independent linear polarization state with arbitrary orientation. This also allows an independent simultaneous polarization-rotation control. The laser beam, both for generating multiple traps and polarization control, has been modulated using a single reflective nematic liquid crystal with parallel alignment. We present experimental results of controlled displacement, orientation and rotation of birefringent particles. In addition, a simple method for estimating and canceling out the primary astigmatism present in the system is presented.
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32.
  • Arwin, Hans, et al. (författare)
  • Cuticle structure of the scarab beetle Cetonia aurata analyzed by regression analysis of Mueller-matrix ellipsometric data
  • 2013
  • Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 21:19, s. 22645-22656
  • Tidskriftsartikel (refereegranskat)abstract
    • Since one hundred years it is known that some scarab beetles reflect elliptically and near-circular polarized light as demonstrated by Michelson for the beetle Chrysina resplendens. The handedness of the polarization is in a majority of cases left-handed but also right-handed polarization has been found. In addition, brilliant colors with metallic shine are observed. The polarization and color effects are generated in the beetle exoskeleton, the so-called cuticle. The objective of this work is to demonstrate that structural parameters and materials optical functions of these photonic structures can be extracted by advanced modeling of spectral multi-angle Mueller-matrix data recorded from beetle cuticles. A dual-rotating compensator ellipsometer is used to record normalized Mueller-matrix data in the spectral range 400 – 800 nm at angles of incidence in the range 25–75°. Analysis of data measured on the scarab beetle Cetonia aurata are presented in detail. The model used in the analysis mimics a chiral nanostructure and is based on a twisted layered structure. Given the complexity of the nanostructure, an excellent fit between experimental and model data is achieved. The obtained model parameters are the spectral variation of the refractive indices of the cuticle layers and structural parameters of the chiral structure.
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33.
  • Arwin, Hans, et al. (författare)
  • Sum decomposition of Mueller-matrix images and spectra of beetle cuticles
  • 2015
  • Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 23:3, s. 1951-1966
  • Tidskriftsartikel (refereegranskat)abstract
    • Spectral Mueller matrices measured at multiple angles of incidence as well as Mueller matrix images are recorded on the exoskeletons (cuticles) of the scarab beetles Cetonia aurata and Chrysina argenteola. Cetonia aurata is green whereas Chrysina argenteola is gold-colored. When illuminated with natural (unpolarized) light, both species reflect left-handed and near-circularly polarized light originating from helicoidal structures in their cuticles. These structures are referred to as circular Bragg reflectors. For both species the Mueller matrices are found to be nondiagonal depolarizers. The matrices are Cloude decomposed to a sum of non-depolarizing matrices and it is found that the cuticle optical response, in a first approximation can be described as a sum of Mueller matrices from an ideal mirror and an ideal circular polarizer with relative weights determined by the eigenvalues of the covariance matrices of the measured Mueller matrices. The spectral and image decompositions are consistent with each other. A regression-based decomposition of the spectral and image Mueller matrices is also presented whereby the basic optical components are assumed to be a mirror and a circular polarizer as suggested by the Cloude decomposition. The advantage with a regression decomposition compared to a Cloude decomposition is its better stability as the matrices in the decomposition are determined a priori. The origin of the depolarizing features are discussed but from present data it is not possible to conclude whether the two major components, the mirror and the circular polarizer are laterally separated in domains in the cuticle or if the depolarization originates from the intrinsic properties of the helicoidal structure.
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34.
  • Asimakopoulou, Eleni Myrto, et al. (författare)
  • Development towards high-resolution kHz-speed rotation-free volumetric imaging
  • 2024
  • Ingår i: Optics Express. - 1094-4087. ; 32:3, s. 4413-4426
  • Tidskriftsartikel (refereegranskat)abstract
    • X-ray multi-projection imaging (XMPI) has the potential to provide rotation-free 3D movies of optically opaque samples. The absence of rotation enables superior imaging speed and preserves fragile sample dynamics by avoiding the centrifugal forces introduced by conventional rotary tomography. Here, we present our XMPI observations at the ID19 beamline (ESRF, France) of 3D dynamics in melted aluminum with 1000 frames per second and 8 µm resolution per projection using the full dynamical range of our detectors. Since XMPI is a method under development, we also provide different tests for the instrumentation of up to 3000 frames per second. As the high-brilliance of 4th generation light-sources becomes more available, XMPI is a promising technique for current and future X-ray imaging instruments.
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35.
  • Aslan, Selin, et al. (författare)
  • Joint ptycho-tomography reconstruction through alternating direction method of multipliers
  • 2019
  • Ingår i: Optics Express. - 1094-4087. ; 27:6, s. 9128-9143
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the extension of ptychography for three-dimensional object reconstruction in a tomography setting. We describe the alternating direction method of multipliers (ADMM) as a generic reconstruction framework to efficiently solve the nonlinear optimization problem. In this framework, the ADMM breaks the joint reconstruction problem into two well-defined subproblems: ptychographic phase retrieval and tomographic reconstruction. In this paper, we use the gradient descent algorithm to solve both problems and demonstrate the efficiency of the proposed approach through numerical simulations. Further, we show that the proposed joint approach relaxes existing requirements for lateral probe overlap in conventional ptychography. Thus, it can allow more flexible data acquisition.
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36.
  • Astra, E., et al. (författare)
  • Dispersion management for nonlinearity mitigation in two-span 28 GBaud QPSK phase-sensitive amplifier links
  • 2017
  • Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 25:12, s. 13163-13173
  • Tidskriftsartikel (refereegranskat)abstract
    • We present an investigation of dispersion map optimization for-span single channel 28 GBaud QPSK transmission systems with phase-sensitive amplifiers (PSAs). In experiments, when the PSA link is operated in a highly nonlinear regime, a 1.4 dB error vector magnitude (EVM) improvement is achieved compared to a one-span optimized dispersion map link due to improved nonlinearity mitigation. The two-span optimized dispersion map of a link differs from the optimized dispersion map of a dispersion managed phase-insensitive amplifier (PIA) link, Simulations show that the performance of the two-span dispersion map optimized PSA link does not improve by residual dispersion optimization. Further, by using the two-span optimized dispersion maps repeatedly in a long-haul PSA link instead of one-span optimized maps, the maximum transmission reach can he improved 1,5 times, (C) 2017 Optical Society of America
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37.
  • Astra, Egon, et al. (författare)
  • Improved mitigation of self-phase modulation induced impairments in 28 GBaud phase-sensitive amplified links
  • 2019
  • Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 27:4, s. 4304-4316
  • Tidskriftsartikel (refereegranskat)abstract
    • The improved mitigation of self-phase modulation (SPM) induced nonlinear impairments by the use of a multi-span dispersion map optimization in 28 GBaud phase-sensitive amplifier (PSA) links is numerically investigated. We show that a four-span dispersion map optimized PSA link provides 2.1 times reach improvement over a single-span optimized PSA link with a total nonlinear phase shift tolerance increase from 2.1 radians to 8.8 radians. Furthermore, the optimized PSA link increases the maximum transmission reach by 6.9 times compared to a single-span optimized in-line dispersion managed phase-insensitive amplifier (PIA) link and 4.3 times reach extension is achieved compared to a dispersion unmanaged PIA link. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
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38.
  • Atlasov, K.A., et al. (författare)
  • Wavelength and loss splitting in directly coupled photonic-crystal defect microcavities
  • 2008
  • Ingår i: Optics Express. - 1094-4087. ; 16:20, s. 16255-16264
  • Tidskriftsartikel (refereegranskat)abstract
    • Coupling between photonic-crystal defect microcavities is observed to result in a splitting not only of the mode wavelength but also of the modal loss. It is discussed that the characteristics of the loss splitting may have an important impact on the optical energy transfer between the coupled resonators. The loss splitting - given by the imaginary part of the coupling strength - is found to arise from the difference in diffractive outof-plane radiation losses of the symmetric and the antisymmetric modes of the coupled system. An approach to control the splitting via coupling barrier engineering is presented. © 2008 Optical Society of America.
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39.
  • Atlasow, Kirill A., et al. (författare)
  • Photonic-crystal microcavity laser with site-controlled quantum-wire active medium
  • 2009
  • Ingår i: Optics Express. - 1094-4087. ; 17:20, s. 18178-18183
  • Tidskriftsartikel (refereegranskat)abstract
    • Site-controlled quantum-wire photonic-crystal microcavity laser is experimentally demonstrated using optical pumping. The single-mode lasing and threshold are established based on the transient laser response, linewidth narrowing, and the details of the non-linear power input-output charateristics. Average-power threshold as low as ~240 nW (absorbed power) and spontaneous emission coupling coefficient β~0.3 are derived.
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40.
  • Augulis, Ramunas, et al. (författare)
  • Two-dimensional electronic spectroscopy with double modulation lock-in detection: enhancement of sensitivity and noise resistance
  • 2011
  • Ingår i: Optics Express. - 1094-4087. ; 19:14, s. 13126-13133
  • Tidskriftsartikel (refereegranskat)abstract
    • In many potential applications of two-dimensional (2D) electronic spectroscopy the excitation energies per pulse are strictly limited, while the samples are strongly scattering. We demonstrate a technique, based on double-modulation of incident laser beams with mechanical choppers, which can be implemented in almost any non-collinear four wave mixing scheme including 2D spectroscopy setup. The technique virtually eliminates artifacts or "ghost" signals in 2D spectra, which arise due to scattering and accumulation of long-lived species. To illustrate the advantages of the technique, we show a comparison of porphyrin J-aggregate 2D spectra obtained with different methods following by discussion. (C) 2011 Optical Society of America
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