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Sökning: L773:1094 4087

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471.
  • Lyubomirskiy, Mikhail, et al. (författare)
  • Planar refractive lenses made of SiC for high intensity nanofocusing
  • 2021
  • Ingår i: Optics Express. - 1094-4087. ; 29:9, s. 14025-14032
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on the manufacturing and testing of the first nanofocusing refractive lenses made of single-crystal silicon carbide. We introduce the fabrication process based on lithography, followed by deep isotropic etching. The lenses were characterized at the energy of 12 keV at the beamline P06 of the synchrotron radiation source PETRA III. A focal spot of 186 nm x 275 nm has been achieved with a lens working distance of 29 mm.
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472.
  • Ma, Guangjin, et al. (författare)
  • Intense circularly polarized attosecond pulse generation from relativistic laser plasmas using few-cycle laser pulses
  • 2016
  • Ingår i: Optics Express. - 1094-4087. ; 24:9, s. 10057-10065
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated the polarization of attosecond light pulses generated from relativistic few-cycle laser pulse interaction with the surface of overdense plasmas using particle-in-cell simulation. Under suitable conditions, a desired polarization state of the generated attosecond pulse can be achieved by controlling the polarization of the incident laser. In particular, an elliptically polarized laser pulse of suitable ellipticity can generate an almost circularly polarized attosecond pulse without compromising the harmonic generation efficiency. The process is thus applicable as a new tabletop circularly-polarized XUV radiation source for probing attosecond phenomena with high temporal resolution.
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473.
  • Maccaferri, N., et al. (författare)
  • Polarizability and magnetoplasmonic properties of magnetic general nanoellipsoids
  • 2013
  • Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 21:8, s. 9875-9889
  • Tidskriftsartikel (refereegranskat)abstract
    • An approach to compute the polarizability tensor of magnetic nanoparticles having general ellipsoidal shape is presented. We find a surprisingly excellent quantitative agreement between calculated and experimental magneto-optical spectra measured in the polar Kerr configuration from nickel nanodisks of large size (exceeding 100 nm) with circular and elliptical shape. In spite of its approximations and simplicity, the formalism presented here captures the essential physics of the interplay between magneto-optical activity and the plasmonic resonance of the individual particle. The results highlight the key role of the dynamic depolarization effects to account for the magneto-optical properties of plasmonic nanostructures.
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474.
  • Maccaferri, Nicolò, et al. (författare)
  • Polarizability and magnetoplasmonic properties of magnetic general nanoellipsoids
  • 2013
  • Ingår i: Optics Express. - : Optica Publishing Group. - 1094-4087. ; 21:8, s. 9875-9889
  • Tidskriftsartikel (refereegranskat)abstract
    • An approach to compute the polarizability tensor of magnetic nanoparticles having general ellipsoidal shape is presented. We find a surprisingly excellent quantitative agreement between calculated and experimental magneto-optical spectra measured in the polar Kerr configuration from nickel nanodisks of large size (exceeding 100 nm) with circular and elliptical shape. In spite of its approximations and simplicity, the formalism presented here captures the essential physics of the interplay between magneto-optical activity and the plasmonic resonance of the individual particle. The results highlight the key role of the dynamic depolarization effects to account for the magneto-optical properties of plasmonic nanostructures.
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475.
  • Magalhaes, Regina, et al. (författare)
  • Fiber-based distributed bolometry
  • 2019
  • Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 27:4, s. 4317-4328
  • Tidskriftsartikel (refereegranskat)abstract
    • Optical fibers are inherently designed to allow no interaction between the guided light and the surrounding optical radiation. Thus, very few optical fiber-based technologies exist in the field of optical radiation sensing. Accomplishing fully-distributed optical radiation sensing appears then as even more challenging since, on top of the lack of sensitivity explained above, we should add the need of addressing thousands of measurement points in a single, continuous optical cable. Nevertheless, it is clear that there exist a number of applications which could benefit from such a distributed sensing scheme, particularly if the sensitivity was sufficiently high to be able to measure correctly variations in optical radiation levels compatible with the earth surface. Distributed optical radiation sensing over large distances could be employed in applications such as Dynamic Line Rating (DLR), where it is known that solar radiation can be an important limiting factor in energy transmission through overhead power cables, and also in other applications such as thermo-solar energy. In this work, we present the proof-of-concept of the first distributed bolometer based on optical fiber technology and capable of detecting absolute changes of irradiance. The core idea of the system is the use of a special fiber coating with high emissivity (e.g., carbon coating or black paint). The high absorption of these coatings translates into a temperature change that can be read with sufficiently high sensitivity using phase-sensitive reflectometry. To demonstrate the concept, we interrogate distinct black-coated optical fibers using a chirped-pulse ÖOTDR, and we readily demonstrate the detection of light with resolutions in the order of 1% of the reference solar irradiance, offering a high-potential technology for integration in the aforementioned applications.
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476.
  • Maire, Guillaume, et al. (författare)
  • High efficiency silicon nitride surface grating couplers
  • 2008
  • Ingår i: Optics Express. - 1094-4087. ; 16:1, s. 328-333
  • Tidskriftsartikel (refereegranskat)abstract
    • High efficiency surface grating couplers for silicon nitride waveguides have been designed, fabricated, and characterized. Coupling efficiencies exceeding 60 % are reported at a wavelength of 1.31 mu m, as well as angular and wavelength -3 dB tolerances of 4 and 50 nm, respectively. When the wavelength is increased from 1310 nm to 1450 nm the coupling efficiency progressively decreases but remains above 20 % at 1450 nm. The influence of the duty ratio of the grating has also been investigated: maximum coupling efficiency was obtained at 50 % duty ratio.
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477.
  • Malik, Rohit, 1984, et al. (författare)
  • Frequency-resolved noise figure measurements of phase (in)sensitive fiber optical parametric amplifiers
  • 2014
  • Ingår i: Optics Express. - : The Optical Society. - 1094-4087 .- 1094-4087. ; 22:23, s. 27821-27832
  • Tidskriftsartikel (refereegranskat)abstract
    • We measure the frequency-resolved noise figure of fiber optical parametric amplifiers both in phase-insensitive and phase-sensitive modes in the frequency range from 0.03 to 3 GHz. We also measure the variation in noise figure due to the degradation in pump optical signal to noise ratio and also as a function of the input signal powers. Noise figure degradation due to stimulated Brillouin scattering is observed.
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478.
  • Malik, Rohit, 1984, et al. (författare)
  • Optical signal to noise ratio improvement through unbalanced noise beating in phase-sensitive parametric amplifiers
  • 2014
  • Ingår i: Optics Express. - : The Optical Society. - 1094-4087 .- 1094-4087. ; 22:9, s. 10477-10486
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the beating of signal and idler waves, which have imbalanced signal to noise ratios, in a phase-sensitive parametric amplifier. Imbalanced signal to noise ratios are achieved in two ways; first by imbalanced noise loading; second by varying idler to signal input power ratio. In the case of imbalanced noise loading the phase-sensitive amplifier improved the signal to noise ratio from 3 to 6 dB, and in the case of varying idler to signal input power ratio, the signal to noise ratio improved from 3 to in excess of 20 dB.
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479.
  • Malm, Erik, et al. (författare)
  • Reference shape effects on Fourier transform holography
  • 2022
  • Ingår i: Optics Express. - 1094-4087. ; 30:21, s. 38424-38438
  • Tidskriftsartikel (refereegranskat)abstract
    • Soft-x-ray holography which utilizes an optics mask fabricated in direct contact with the sample, is a widely applied x-ray microscopy method, in particular, for investigating magnetic samples. The optics mask splits the x-ray beam into a reference wave and a wave to illuminate the sample. The reconstruction quality in such a Fourier-transform holography experiment depends primarily on the characteristics of the reference wave, typically emerging from a small, high-aspect-ratio pinhole in the mask. In this paper, we study two commonly used reference geometries and investigate how their 3D structure affects the reconstruction within an x-ray Fourier holography experiment. Insight into these effects is obtained by imaging the exit waves from reference pinholes via high-resolution coherent diffraction imaging combined with three-dimensional multislice simulations of the x-ray propagation through the reference pinhole. The results were used to simulate Fourier-transform holography experiments to determine the spatial resolution and precise location of the reconstruction plane for different reference geometries. Based on our findings, we discuss the properties of the reference pinholes with view on application in soft-x-ray holography experiments.
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480.
  • Malm, Erik, et al. (författare)
  • Singleshot polychromatic coherent diffractive imaging with a high-order harmonic source
  • 2020
  • Ingår i: Optics Express. - 1094-4087. ; 28:1, s. 394-404
  • Tidskriftsartikel (refereegranskat)abstract
    • Singleshot polychromatic coherent diffractive imaging is performed with a high-intensity high-order harmonic generation source. The coherence properties are analyzed and several reconstructions show the shot-to-shot fluctuations of the incident beam wavefront. The method is based on a multi-step approach. First, the spectrum is extracted from double-slit diffraction data. The spectrum is used as input to extract the monochromatic sample diffraction pattern, then phase retrieval is performed on the quasi-monochromatic data to obtain the sample's exit surface wave. Reconstructions based on guided error reduction (ER) and alternating direction method of multipliers (ADMM) are compared. ADMM allows additional penalty terms to be included in the cost functional to promote sparsity within the reconstruction.
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