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An in-situ end-point detection technique for ion-beam etching is presented. A laser beam of the same wavelength and polarization as those in the intended application of the grating is fed into the vacuum chamber, and the beam retr...
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An in-situ end-point detection technique for ion-beam etching is presented. A laser beam of the same wavelength and polarization as those in the intended application of the grating is fed into the vacuum chamber, and the beam retro-diffracted by the grating under etching is extracted and detected outside the chamber. This arrangement greatly simplifies the end-point detection. Modeling the grating diffraction with a rigorous diffraction grating computer program, we can satisfactorily simulate the evolution of the diffraction intensity during the etching process and consequently, we can accurately predict the end-point. Employing the proposed technique, we have reproducibly fabricated multilayer dielectric gratings with diffraction efficiencies of more than 92%.
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Magnetic coherence gratings have been created in a thermal beam of rubidium atoms. The coherence gratings involve superposition of magnetic sublevels of a single hyperfine ground state. These gratings are created via interaction w...
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Magnetic coherence gratings have been created in a thermal beam of rubidium atoms. The coherence gratings involve superposition of magnetic sublevels of a single hyperfine ground state. These gratings are created via interaction with a single pulse that drives a two-photon transition between magnetic sublevels of the ground state. After the grating dephases due to the velocity distribution of the atoms, it is revived by the action of a second pulse, an effect that is similar to a photon echo. Such experiment is a first step toward generating periodic atomic structures using a high-flux atomic beam. Here, we present the experimental results and provide a detailed description of the apparatus that produces a high flux beam of thermal rubidium atoms.
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Using a combination of rigorous coupled-wave analysis and simulated annealing, parallel-face slanted surface-relief gratings (PPSSRGs) are optimized. For substrate-mode optical interconnects, profiles are presented for both polyme...
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Using a combination of rigorous coupled-wave analysis and simulated annealing, parallel-face slanted surface-relief gratings (PPSSRGs) are optimized. For substrate-mode optical interconnects, profiles are presented for both polymer and silicon PFSSRGs for both TE and TM polarizations at normal incidence with grating periods designed to give a 45° output angle in the negative-first forward-diffracted order. The resulting diffraction efficiencies range from 70% to 99%, with a majority of the optimized profiles yielding over 90%. Optimized polymer profiles for TE and TM polarizations exhibit similar high diffraction efficiencies, but the TM profiles generally require greater groove depths. Silicon profiles optimized for TM polarization have greater diffraction efficiencies than those for TE polarization. Profiles that can feasibly be fabricated are identified, and sensitivities to groove depth, filling factor, slant angle, and incident angle are shown to be modest.
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In a highly Ge-doped photosensitive fiber co-doped with phosphorus and fluorine and with a doped inner cladding, we observed, during annealing experiments, an anomalous variation of the FBG strength as a function of temperature an...
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In a highly Ge-doped photosensitive fiber co-doped with phosphorus and fluorine and with a doped inner cladding, we observed, during annealing experiments, an anomalous variation of the FBG strength as a function of temperature and time. This characteristic only occurred when the fiber had been loaded with hydrogen. During a stepwise temperature increase from room temperature to 1200℃ with 15 min dwell times, the gratings showed, after an initial thermal decay, in two distinct temperature ranges a significant increase in reflectivity with time. One range with an increase in reflectivity was found between 850 ℃ and 1000 ℃. The behavior of the FBGs in this range was very similar to that known from chemical composition or regenerated gratings. Another temperature range with increasing reflectivity was found between 500 ℃ and 700 ℃, followed by a strong decrease in reflectivity at temperatures between 750 ℃ and 800 ℃. Both regimes of regeneration might be associated with changes in the core and the doped inner cladding of this type of fiber. At different temperatures the drift behavior of λ_B and Δn_(AC) was investigated. In specific temperature regions a positive wavelength drift combined with a decrease in Δn_(AC) has been observed. This is in contradiction to the standard thermal decay model and seems to be a characteristic of regenerated gratings.
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This work presents a theoretical explanation and experimental evidence of pulses- intensity displacement and pulse- broadening profiles of a Q-switched and mode-locked Nd: YAG laser- pumped distributed feedback dye laser (DFDL). E...
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This work presents a theoretical explanation and experimental evidence of pulses- intensity displacement and pulse- broadening profiles of a Q-switched and mode-locked Nd: YAG laser- pumped distributed feedback dye laser (DFDL). Experimental results followed by a theoretical simulation indicate that DFDL pulses peaked noticeably later than their corresponding Nd: YAG laser pulses. The DFDL pulse corresponding to the peak-power pump laser pulse occurs few pulses later than the expected location. The observed and simulated delays were found to depend upon the inter-pulse periods of the pumping Q-switched and mode-locked laser. We report the theoretical basis for the influence of temperature grating relaxation times on the dye laser's pulse characteristics, and apply the transient grating technique to measure the refractive index of a lasing dye solution. Results indicate that the thermal effects of preceding pulses integrate the gain for receding pulses. These results provide a good understanding of temperature grating relaxation times and their impact on the lasing characteristics of DFDL.
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Miniaturized optical instruments have become very important in industry as smart phones and tablet PCs increase in popularity. A chronology of spectrometer development shows that a simple numerical point of view affords important ...
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Miniaturized optical instruments have become very important in industry as smart phones and tablet PCs increase in popularity. A chronology of spectrometer development shows that a simple numerical point of view affords important insights. A tiny spectrometer, which is smaller than a few millimeters size, cannot easily rely on the conventional Fraunhofer diffraction due to its optical criterion limit. As an alternate solution to build smaller spectrometers, a Fresnel spectrometer chip with a gradient line grating is attractive. The fabricated Fresnel spectrometers have optical path volumes of about 1 mm~3 and spectral resolutions of 10 to 23 nm.
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We analyze the far-field diffraction pattern produced by linear spatial chirped gratings. An intuitive analytical interpretation of the generated diffraction orders is proposed for gratings with linear variation of the period and ...
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We analyze the far-field diffraction pattern produced by linear spatial chirped gratings. An intuitive analytical interpretation of the generated diffraction orders is proposed for gratings with linear variation of the period and linear variation of the spatial frequency. Also, experiments using Gaussian beams and plane wave illumination are performed. The analytical expressions are compared to numerical and experimental results, showing a high agreement. Chirped gratings can be implemented in interesting applications: we analyze how they can be used as a deflector, since tunable direction of diffracted orders can be achieved by displacing laterally the grating with respect to the incident light beam. Also the angular width of diffraction orders can be controlled and chirped gratings can be used to generate uniform illumination over a controlled angular range. These two applications have also been experimentally shown. (C) 2018 Elsevier Ltd. All rights reserved.
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We present a semi-analytical model that quantitatively predicts the transmission, the absorption and the resonance locations of one-dimensional lamellar metallic gratings with subwavelength slit apertures. The model relies on the ...
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We present a semi-analytical model that quantitatively predicts the transmission, the absorption and the resonance locations of one-dimensional lamellar metallic gratings with subwavelength slit apertures. The model relies on the fact that subwavelength apertures perforated in metallic films behave like monomode waveguides and provide Airy-like formulae for the transmission and reflection coefficients. Limitations are outlined for too shallow grating depths.
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A novel approach to the design and analysis of space-variant polarization elements using computer-generated subwavelength metal stripe gratings is presented. We demonstrate that by locally controlling the direction and period of t...
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A novel approach to the design and analysis of space-variant polarization elements using computer-generated subwavelength metal stripe gratings is presented. We demonstrate that by locally controlling the direction and period of the grating any desired space-variant polarization state manipulation can be obtained. We illustrate our approach with two distinct types of manipulators: space-variant polarizers and space-variant polarization state transformations. The elements were formed on GaAs as well as ZnSe substrates and designed for laser radiation at 10.6 μm. The results include full space-variant polarization calculations and measurements and show high-quality space-variant polarized beams with a polarization purity of over 99%.
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We propose a deterministic design method of a blazed grating consisting of a binary grating with subwavelength structures for a multilevel phase modulation. The feasible shapes of binary subwave length microstructures are restrict...
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We propose a deterministic design method of a blazed grating consisting of a binary grating with subwavelength structures for a multilevel phase modulation. The feasible shapes of binary subwave length microstructures are restricted to a few kinds of surface profiles by constraints in an actual fabrication technique. The relationship between the feasible shapes of binary subwavelength microstructures and their phase modulations can be calculated by an electromagnetic analysis and tabulated. Using the relationship, a deterministic design of a binary grating with subwavelength structures is simply realized. We have designed the binary blazed grating with subwavelength structures and investigated its performance. Its diffraction efficiency is in good agreement with that by a conventional statistical design method.
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