| 1. |
- Aghaeipour, Mahtab, et al.
(författare)
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Optical response of wurtzite and zinc blende GaP nanowire arrays
- 2015
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Ingår i: Optics Express. - 1094-4087. ; 23:23, s. 30177-30187
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Tidskriftsartikel (refereegranskat)abstract
- We compare the optical response of wurtzite and zinc blende GaP nanowire arrays for varying geometry of the nanowires. We measure reflectance spectra of the arrays and extract from these measurements the absorption in the nanowires. To support our experimental findings and to allow for more detailed investigations of the optical response of the nanowire arrays than possible in experiments, we perform electromagnetic modeling. This modeling highlights the validity of the extraction of the absorptance from reflectance spectra, as well as limitations of the extraction due to anti-reflection properties of the nanowires. In our combined experimental and theoretical study, we find for both zinc blende and wurtzite nanowires an absorption resonance that can be tuned into the ultraviolet by decreasing the diameter of the nanowires. This peak stops blue-shifting with decreasing nanowire diameter at a wavelength of approximately 330 nm for zinc blende GaP. In contrast, for the wurtzite GaP nanowires, the resonance continues blue-shifting at 310 nm for the smallest diameters we succeeded in fabricating. We interpret this as a difference in refractive index between wurtzite and zinc blende GaP in this wavelength region. These results open up for optical applications through resonant absorption in the visible and ultraviolet wavelength regions with both zinc blende and wurtzite GaP nanowire arrays. Notably, zinc blende and wurtzite GaP support resonant absorption deeper into the ultraviolet region than previously found for zinc blende and wurtzite InP and InAs. (C) 2015 Optical Society of America
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| 2. |
- Alcusa-Sáez, E. P., et al.
(författare)
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Acousto-optic interaction in polyimide coated optical fibers with flexural waves
- 2017
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 25:15, s. 17167-17173
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Tidskriftsartikel (refereegranskat)abstract
- Acousto-optic coupling in polyimide-coated single-mode optical fibers using flexural elastic waves is demonstrated. The effect of the polyimide coating on the acousto-optic interaction process is analyzed in detailed. Theoretical and experimental results are in good agreement. Although the elastic attenuation is significant, we show that acousto-optic coupling can be produced with a reasonably good efficiency. To our knowledge, it is the first experimental demonstration of acousto-optic coupling in optical fibers with robust protective coating.
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| 3. |
- Amer, Eynas, et al.
(författare)
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Stimulated Raman scattering detection for chemically specific time-resolved imaging of gases
- 2016
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Ingår i: Optics Express. - 1094-4087. ; 24:9, s. 9984-9993
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Tidskriftsartikel (refereegranskat)abstract
- stimulated Raman scattering (SRS) imaging technique based on spatial modulation of the pump beam has been used to study gases. The SRS gain signal was separated from the Stokes beam background in the spatial frequency domain. The SRS signal shows linear behaviour with the gas pressure at a range from 1.0 to 8.0 bars. The signal is linearly proportional to the pump beam intensity while it is enhanced with increasing the Stokes beam intensity to a certain limit than it saturates. Further, the chemical specificity of the technique has been investigated. Two sharp peaks with line width at half maximum of about 0.30 nm have been obtained at Stokes beam wavelengths of 629.93 nm and 634.05 nm corresponding to the methane and ethylene gases, respectively. The results show that SRS imaging is a promising technique to provide chemical specificity as well as spatial and temporal information of gaseous species
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| 4. |
- Arwin, Hans, et al.
(författare)
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Sum decomposition of Mueller-matrix images and spectra of beetle cuticles
- 2015
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 23:3, s. 1951-1966
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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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| 5. |
- Astra, E., et al.
(författare)
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Dispersion management for nonlinearity mitigation in two-span 28 GBaud QPSK phase-sensitive amplifier links
- 2017
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 25:12, s. 13163-13173
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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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| 6. |
- Baghban, Mohammad Amin, et al.
(författare)
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Bragg gratings in thin-film LiNbO3 waveguides
- 2017
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 25:26, s. 32323-32332
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Tidskriftsartikel (refereegranskat)abstract
- We design, fabricate and characterize sidewall corrugated Bragg gratings in a high confinement integrated optics lithium niobate platform, comprising submicrometric photonic wires, tapers and grating couplers to interface off-chip standard telecom optical fibers. We analyze the grating performance as band-rejection filter for TE-polarized signals in the telecom C-band, considering both rectangular and sinusoidal sidewall profiles, and demonstrate record extinction ratios as high as 27 dB and rejection bandwidths as narrow as 3 nm. The results show the potential for an efficient integration of novel photonic functionalities into low-footprint LiNbO3 nonlinear and electro-optical waveguide devices.
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| 7. |
- Bagschik, K., et al.
(författare)
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Spatial coherence determination from the Fourier analysis of a resonant soft X-ray magnetic speckle pattern
- 2016
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 24:20, s. 23162-23176
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Tidskriftsartikel (refereegranskat)abstract
- We present a method to determine the two-dimensional spatial coherence of synchrotron radiation in the soft X-ray regime by analyzing the Fourier transform of the magnetic speckle pattern from a ferromagnetic film in a multidomain state. To corroborate the results, a Young's double-pinhole experiment has been performed. The transverse coherence lengths in vertical and horizontal direction of both approaches are in a good agreement. The method presented here is simple and gives a direct access to the coherence properties of synchrotron radiation without nanostructured test objects.
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| 8. |
- Boyko, Andrey A., et al.
(författare)
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Intracavity-pumped, cascaded AgGaSe2 optical parametric oscillator tunable from 5.8 to 18 mu m
- 2015
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 23:26, s. 33460-33465
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Tidskriftsartikel (refereegranskat)abstract
- A AgGaSe2 nonlinear crystal placed in a coupled cavity is intracavity pumped by the similar to 1.85-mu m signal pulses of a 1.064-mu m pumped Rb: PPKTP doubly-resonant optical parametric oscillator (OPO) operating at a repetition rate of 100 Hz. Using two samples cut for type-I and II phase-matching, the overall idler tunability of the singly-resonant AgGeSe2 OPO covers an unprecedented spectral range from 5.8 to similar to 18 mu m in the mid-IR.
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| 9. |
- Burza, Matthias, et al.
(författare)
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Dispersion and monochromatization of x-rays using a beryllium prism
- 2015
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Ingår i: Optics Express. - 1094-4087. ; 23:2, s. 620-627
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate experimentally and numerically that an x-ray prism made of beryllium can be used to disperse and monochromatize x-rays. A polished beryllium cuboid was employed as refractive and dispersive optics. The results of a proof-of-principle experiment and methods of performance optimization are presented. The spatial separation of undulator harmonics and their subsequent selection using a slit are described. A numerical study, assuming realistic beam and beamline parameters, suggests that undulator harmonics can be spatially separated in the range from 3 keV to beyond 20 keV, while maintaining throughput above 50%. Refractive optics is particularly suitable for low-repetition-rate sources such as free-electron lasers and other LINAC-based short-pulse sources. (C) 2015 Optical Society of America
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| 10. |
- Caleman, Carl, et al.
(författare)
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Ultrafast self-gating Bragg diffraction of exploding nanocrystals in an X-ray laser
- 2015
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Ingår i: Optics Express. - 1094-4087. ; 23:2, s. 1213-1231
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Tidskriftsartikel (refereegranskat)abstract
- In structural determination of crystalline proteins using intense femtosecond X-ray lasers, damage processes lead to loss of structural coherence during the exposure. We use a nonthermal description for the damage dynamics to calculate the ultrafast ionization and the subsequent atomic displacement. These effects degrade the Bragg diffraction on femtosecond time scales and gate the ultrafast imaging. This process is intensity and resolution dependent. At high intensities the signal is gated by the ionization affecting low resolution information first. At lower intensities, atomic displacement dominates the loss of coherence affecting high-resolution information. We find that pulse length is not a limiting factor as long as there is a high enough X-ray flux to measure a diffracted signal.
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