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Träfflista för sökning "L773:1094 4087 ;lar1:(umu)"

Sökning: L773:1094 4087 > Umeå universitet

  • Resultat 1-10 av 56
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1.
  • Abd Alrahman, Chadi, et al. (författare)
  • Cavity-enhanced optical frequency comb spectroscopy of high-temperature H2O in a flame
  • 2014
  • Ingår i: Optics Express. - 1094-4087. ; 22:11, s. 13889-13895
  • Tidskriftsartikel (refereegranskat)abstract
    • We demonstrate near-infrared cavity-enhanced optical frequency comb spectroscopy of water in a premixed methane/air flat flame. The detection system is based on an Er:fiber femtosecond laser, a high finesse optical cavity containing the flame, and a fast-scanning Fourier transform spectrometer (FTS). High absorption sensitivity is obtained by the combination of a high-bandwidth two-point comb-cavity lock and auto-balanced detection in the FTS. The system allows recording high-temperature water absorption spectra with a resolution of 1 GHz and a bandwidth of 50 nm in an acquisition time of 0.4 s, with absorption sensitivity of 4.2 x 10 (9) cm(-1) Hz(-1/2) per spectral element.
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2.
  • Ako, Thomas, et al. (författare)
  • Design of invisibility cloaks with an open tunnel
  • 2010
  • Ingår i: Optics Express. - : Optical Society of America. - 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.
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3.
  • Amotchkina, Tatiana, et al. (författare)
  • Stress compensation with antireflection coatings for ultrafast laser applications : from theory to practice
  • 2014
  • Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 22:24, s. 30387-30393
  • Tidskriftsartikel (refereegranskat)abstract
    • Each complicated coating, in particular, a dispersive mirror consists of dozens of layers. Thin films layers have mechanical stresses. After summing up stresses from all layers, the resulting stress is high enough to bend even a relatively thick substrate. To avoid this effect we suggest depositing an antireflection coating (AR) at the back-side of the substrate which together with suppression of unwanted reflections from the back side will also compensate this stress. We demonstrate unique, extremely thick and sophisticated AR coating consisting of 71 layers with the total physical thickness of 7.5 µm. This AR coating completely compensates stress from the dispersive mirror coated on the front side and minimizes unwanted reflections.
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4.
  • Centeno, R., et al. (författare)
  • External cavity diode laser-based detection of trace gases with NICE-OHMS using current modulation
  • 2015
  • Ingår i: Optics Express. - 1094-4087. ; 23:5, s. 6277-6282
  • Tidskriftsartikel (refereegranskat)abstract
    • We combine an external cavity diode laser with noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) using current modulation. With a finesse of 1600, we demonstrate noise equivalent absorption sensitivities of 4.1 x 10(-10) cm(-1) Hz(-1/2), resulting in sub-ppbv detection limits for Doppler-broadened transitions of CH4 at 6132.3 cm(-1), C2H2 at 6578.5 cm(-1) and HCN at 6541.7 cm(-1). The system is used for hydrogen cyanide detection from sweet almonds.
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5.
  • Cheddad, Abbas, et al. (författare)
  • Improving signal detection in emission optical projection tomography via single source multi-exposure image fusion
  • 2013
  • Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 21:14, s. 16584-16604
  • Tidskriftsartikel (refereegranskat)abstract
    • We demonstrate a technique to improve structural data obtained from Optical Projection Tomography (OPT) using Image Fusion (IF) and contrast normalization. This enables the visualization of molecular expression patterns in biological specimens with highly variable contrast values. In the approach, termed IF-OPT, different exposures are fused by assigning weighted contrasts to each. When applied to projection images from mouse organs and digital phantoms our results demonstrate the capability of IF-OPT to reveal high and low signal intensity details in challenging specimens. We further provide measurements to highlight the benefits of the new algorithm in comparison to other similar methods.
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6.
  • Chen, Xi, et al. (författare)
  • Photothermally tunable silicon-microring-based optical add-drop filter through integrated light absorber
  • 2014
  • Ingår i: Optics Express. - : Optica Publishing Group. - 1094-4087. ; 22:21, s. 25233-25241
  • Tidskriftsartikel (refereegranskat)abstract
    • An optically pumped thermo-optic (TO) silicon ring add-drop filter with fast thermal response is experimentally demonstrated. We propose that metal-insulator-metal (MIM) light absorber can be integrated into silicon TO devices, acting as a localized heat source which can be activated remotely by a pump beam. The MIM absorber design introduces less thermal capacity to the device, compared to conventional electrically-driven approaches. Experimentally, the absorber-integrated add-drop filter shows an optical response time of 13.7 μs following the 10%–90% rule (equivalent to a exponential time constant of 5 μs) and a wavelength shift over pump power of 60 pm/mW. The photothermally tunable add-drop filter may provide new perspectives for all-optical routing and switching in integrated Si photonic circuits.
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7.
  • Chen, Yiting, et al. (författare)
  • Honeycomb-lattice plasmonic absorbers at NIR : anomalous high-order resonance
  • 2013
  • Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 21:18, s. 20873-20879
  • Tidskriftsartikel (refereegranskat)abstract
    • We design, fabricate and characterize a plasmonic honeycomb lattice absorber with almost perfect absorption at 1140 nm over a wide incident angle range. This absorber also possesses a narrow-band, angle- and polarization-dependent high-order resonance in the short-wavelength range, with a bandwidth of 19 nm and angle sensitivity of 3 nm per degree. The nature of this high-order absorption band is analyzed through finite-element simulations. We believe it is due to Bragg coupling of the incident light to the backward-propagating surface plasmon polariton through the periodic modulation of the structure.Such fine absorption bands can find applications in plasmonic sensors and spectrally selective thermal emitters.
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8.
  • Chen, Yiting, et al. (författare)
  • Metal-insulator-metal plasmonic absorbers : influence of lattice
  • 2014
  • Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 22:25, s. 30807-30814
  • Tidskriftsartikel (refereegranskat)abstract
    • We experimentally demonstrate three kinds of metal-insulator-metal based plasmonic absorbers consisting of arrays of gold nanodisks distributed in different lattices, including square, triangular and honeycomb lattices. It’s found that resonances originated from localized surface plasmon undergo little changes with respect to different lattice distributions of the nanodisks. The interparticle coupling results in a minor bandwidth broadening of the fundamental mode. Different from square- and triangular-lattice absorbers, honeycomb-lattice absorber possesses a unique red-shifting (with respect to incident angles) narrow-band high-order mode, which originates from coupling of incident light to propagating surface plasmon polariton (SPP) waves. Similar high-order mode can also be generated in square-lattice absorber by increasing the period so that a smaller reciprocal lattice vector can be introduced to excite the SPP mode. Furthermore, we show that two types of resonances can interact and create Fano-type resonances. The simulation results agree well with the experimental results.
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9.
  • Chen, Yiting, et al. (författare)
  • Plasmonic analog of microstrip transmission line and effect of thermal annealing on its propagation loss
  • 2013
  • Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 21:2, s. 1639-1644
  • Tidskriftsartikel (refereegranskat)abstract
    • We fabricated a plasmonic analog of the microwave microstrip transmission line and measured its propagation loss before and after thermal annealing. It is found that its propagation loss at 980 nm wavelength can be reduced by more than 50%, from 0.45 to 0.20 dB/μm, after thermal annealing at 300 °C. The reduction in loss can be attributed to the improved gold surface condition and probably also to the change in the metal’s inner structure. Less evident loss reduction is noticed at 1550 nm, which is owing to extremely small portion of the modal electric field located in the metal regions at this wavelength.
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10.
  • Dai, Jin, et al. (författare)
  • Light absorber based on nano-spheres on a substrate reflector
  • 2013
  • Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 21:6, s. 6697-6706
  • Tidskriftsartikel (refereegranskat)abstract
    • We systematically study a type of plasmonic light absorber based on a monolayer of gold nano-spheres with less than 30 nm in diameters deposited on top of a continuous gold substrate. The influences of particle size, inter-particle distance, particle-substrate spacer size etc on the resonance are studied thoroughly with a 3D finite-element method. We identified that the high-absorption resonance is mainly due to gap plasmon (coupled through particle bodies) when the separation between neighboring nano-spheres is small enough, such as close to 1 nm; at larger particle separations, the resonance is dominated by particle dipoles (coupled through the host dielectric). Experimentally, an absorber was fabricated based on chemically-synthesized gold nanoparticles coated with silica shell. The absorber shows a characteristic absorption band around 810 nm with a maximum absorbance of approximately 90%, which agrees reasonably well with our numerical calculation. The fabrication technique can be easily adapted for devising efficient light absorbers of large areas.
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  • Resultat 1-10 av 56

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