The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform
Izabela Naydenova - One of the best experts on this subject based on the ideXlab platform.
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humidity and temperature induced changes in the diffraction efficiency and the Bragg Angle of slanted photopolymer based holographic gratings
Sensors and Actuators B-chemical, 2017Co-Authors: Tatsiana Mikulchyk, James Walshe, Dervil Cody, Suzanne Martin, Izabela NaydenovaAbstract:Abstract This work explores the humidity and temperature response of volume phase slanted gratings recorded in photopolymers with varied chemical composition. Acrylamide and diacetone acrylamide were used as monomers and triethanolamine and N -phenylglycine were used as photoinitiators. The study demonstrates that the response of photopolymer-based holographic gratings to relative humidity (RH) and temperature (T) can be tuned by alteration of the photopolymer composition. Humidity and temperature response of the holograms has been characterized by recording Bragg selectivity curves of transmission gratings and by monitoring the position of the maximum intensity in the spectral response of reflection gratings. Investigation of the humidity response in the range of 20–90% RH reveals that photopolymers containing triethanolamine are more responsive to moisture than photopolymers containing N -phenylglycine and display significant sensitivity to relative humidity above 40%. Full reversibility of humidity induced changes in gratings recorded in diacetone acrylamide-based photopolymer is confirmed at RH ≤ 60%. Exposure to RH ≥ 70% leads to irreversible changes in these gratings. The temperature response of slanted transmission gratings was investigated in the temperature range of 20–60 °C. Exposure of the photopolymer layers containing triethanolamine to elevated temperature was found to cause layer shrinkage due to desorption of absorbed water. Sealed layers containing triethanolamine, however, demonstrated swelling due to the effect of thermal expansion. The photopolymer layers containing N -phenylglycine were found to be unresponsive to temperature changes below 30 °C and have sensitivity to temperature above 30 °C.
Jiro Matsuo - One of the best experts on this subject based on the ideXlab platform.
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characterization of structural dynamics of vo2 thin film on c al2o3 using in air time resolved x ray diffraction
Physical Review B, 2010Co-Authors: Masaki Hada, Kunio Okimura, Jiro MatsuoAbstract:The lattice motion and displacement of atoms in the unit cell in vanadium dioxide $({\text{VO}}_{2})$ grown on $c{\text{-Al}}_{2}{\text{O}}_{3}$ were characterized by static and time-resolved x-ray diffraction (XRD) measurements. The monoclinic-tetragonal phase transition of the ${\text{VO}}_{2}$ unit cell and the twist motion of vanadium atoms in the unit cell were observed. The time-resolved XRD measurements were performed in air using a tabletop high-repetition femtosecond laser. The results obtained from the time-resolved XRD measurements suggested that the unit cell of the low-temperature monoclinic ${\text{VO}}_{2}$ transformed into the high-temperature tetragonal phase extremely rapidly (within 25 ps); however, the atoms in the unit cell fluctuated or vibrated about the center of the tetragonal coordinates, which abated within $\ensuremath{\sim}100\text{ }\text{ps}$. Thus, the time-resolved XRD measurements of the Bragg Angle, intensity, and width of the diffraction lines simultaneously revealed the phase transition of ${\text{VO}}_{2}$ and the atomic motion in the unit cell.
Luc Simard - One of the best experts on this subject based on the ideXlab platform.
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the infrared imaging spectrograph iris for tmt volume phase holographic grating performance testing and discussion
arXiv: Instrumentation and Methods for Astrophysics, 2014Co-Authors: Shaojie Chen, Elliot Meyer, James E Larkin, Etsuko Mieda, Shelley A. Wright, Anna M Moore, Jerome Maire, Luc SimardAbstract:Maximizing the grating efficiency is a key goal for the first light instrument IRIS (Infrared Imaging Spectrograph) currently being designed to sample the diffraction limit of the TMT (Thirty Meter Telescope). Volume Phase Holographic (VPH) gratings have been shown to offer extremely high efficiencies that approach 100% for high line frequencies (i.e., 600 to 6000l/mm), which has been applicable for astronomical optical spectrographs. However, VPH gratings have been less exploited in the near-infrared, particularly for gratings that have lower line frequencies. Given their potential to offer high throughputs and low scattered light, VPH gratings are being explored for IRIS as a potential dispersing element in the spectrograph. Our team has procured near-infrared gratings from two separate vendors. We have two gratings with the specifications needed for IRIS current design: 1.51-1.82{\mu}m (H-band) to produce a spectral resolution of 4000 and 1.19- 1.37 {\mu}m (J-band) to produce a spectral resolution of 8000. The center wavelengths for each grating are 1.629{\mu}m and 1.27{\mu}m, and the groove densities are 177l/mm and 440l/mm for H-band R=4000 and J-band R=8000, respectively. We directly measure the efficiencies in the lab and find that the peak efficiencies of these two types of gratings are quite good with a peak efficiency of ~88% at the Bragg Angle in both TM and TE modes at H-band, and 90.23% in TM mode, 79.91% in TE mode at J-band for the best vendor. We determine the drop in efficiency off the Bragg Angle, with a 20-23% decrease in efficiency at H-band when 2.5 degree deviation from the Bragg Angle, and 25%-28% decrease at J-band when 5{\deg} deviation from the Bragg Angle.
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The infrared imaging spectrograph (IRIS) for TMT: volume phase holographic grating performance testing and discussion
Ground-based and Airborne Instrumentation for Astronomy V. Proc. SPIE, 2014Co-Authors: Shaojie Chen, Elliot Meyer, James E Larkin, Etsuko Mieda, Judith Maire, Shelley A. Wright, Anna M Moore, Luc SimardAbstract:Maximizing the grating efficiency is a key goal for the first light instrument IRIS (Infrared Imaging Spectrograph) currently being designed to sample the diffraction limit of the TMT (Thirty Meter Telescope). Volume Phase Holographic (VPH) gratings have been shown to offer extremely high efficiencies that approach 100% for high line frequencies (i.e., 600 to 6000l/mm), which has been applicable for astronomical optical spectrographs. However, VPH gratings have been less exploited in the near-infrared, particularly for gratings that have lower line frequencies. Given their potential to offer high throughputs and low scattered light, VPH gratings are being explored for IRIS as a potential dispersing element in the spectrograph. Our team has procured near-infrared gratings from two separate vendors. We have two gratings with the specifications needed for IRIS current design: 1.51-1.82μm (H-band) to produce a spectral resolution of 4000 and 1.19-1.37μm (J-band) to produce a spectral resolution of 8000. The center wavelengths for each grating are 1.629μm and 1.27μm, and the groove densities are 177l/mm and 440l/mm for H-band R=4000 and J-band R=8000, respectively. We directly measure the efficiencies in the lab and find that the peak efficiencies of these two types of gratings are quite good with a peak efficiency of ~88% at the Bragg Angle in both TM and TE modes at H-band, and 90.23% in TM mode, 79.91% in TE mode at J-band for the best vendor. We determine the drop in efficiency off the Bragg Angle, with a 20-23% decrease in efficiency at H-band when 2.5° deviation from the Bragg Angle, and 25%-28% decrease at J-band when 5° deviation from the Bragg Angle.
G Bushnellwye - One of the best experts on this subject based on the ideXlab platform.
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nanosecond time resolved crystallography of photo induced species case study and instrument development for high resolution excited state single crystal structure determination
Faraday Discussions, 2003Co-Authors: Jacqueline M Cole, Paul R Raithby, Michael Wulff, Friedrich Schotte, Anton Plech, Simon J Teat, G BushnellwyeAbstract:This work describes one of the first stages in the development of time-resolved photo-induced small-molecule single-crystal diffraction, whereby transient electron density perturbations, with lifetimes down to the nanosecond level, can be resolved at the atomic level. Knowledge of such ephemeral electronic effects is likely to yield key information regarding the origins of certain important physical properties, e.g. luminescent and non-linear optical effects, since it will allow the dynamics of electron density to be identified and quantified, and it is this that underpins such phenomena in a given molecule. The experimental methodology employs phase-locking pump–probe techniques such that the inherent time-structure of a synchrotron X-ray beam (nanoseconds) is harnessed and time-gated in-phase with a femtosecond laser. The resultant beams, made coincident on the crystal in a periodic manner, and a diffraction pattern are recorded as a function of the Bragg Angle, θ. Such technology is based upon the pioneering work carried out in sub-nanosecond time-resolved crystallography of macromolecular biological moieties (non-atomic resolution) at the ESRF, although one crucial difference here is the use of monochromatic irradiation and oscillatory motion rather than Laue ‘snapshot’ methodology, so that atomic resolution is possible. The experimental details of a case study conducted on ID9 at the ESRF, France, are described, whereby the feasibility of the excited-state structure determination of a luminescent rhenium carbene complex, [HNCH2CH2NHCRe(2,2′-bipyridine)(CO)3]Br, is realised. Key experimental parameters that are required for the success of such an experiment are discussed in the light of this study, together with other feasibility work conducted at the SRS, UK, and in the laboratory. Plans, designs and tests for the implementation of this technique in the UK, first at the SRS, and then at DIAMOND, the forthcoming UK synchrotron, are described, in particular with reference to the world-leading potential that DIAMOND could lend toward the development of this technique.
Tatsiana Mikulchyk - One of the best experts on this subject based on the ideXlab platform.
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humidity and temperature induced changes in the diffraction efficiency and the Bragg Angle of slanted photopolymer based holographic gratings
Sensors and Actuators B-chemical, 2017Co-Authors: Tatsiana Mikulchyk, James Walshe, Dervil Cody, Suzanne Martin, Izabela NaydenovaAbstract:Abstract This work explores the humidity and temperature response of volume phase slanted gratings recorded in photopolymers with varied chemical composition. Acrylamide and diacetone acrylamide were used as monomers and triethanolamine and N -phenylglycine were used as photoinitiators. The study demonstrates that the response of photopolymer-based holographic gratings to relative humidity (RH) and temperature (T) can be tuned by alteration of the photopolymer composition. Humidity and temperature response of the holograms has been characterized by recording Bragg selectivity curves of transmission gratings and by monitoring the position of the maximum intensity in the spectral response of reflection gratings. Investigation of the humidity response in the range of 20–90% RH reveals that photopolymers containing triethanolamine are more responsive to moisture than photopolymers containing N -phenylglycine and display significant sensitivity to relative humidity above 40%. Full reversibility of humidity induced changes in gratings recorded in diacetone acrylamide-based photopolymer is confirmed at RH ≤ 60%. Exposure to RH ≥ 70% leads to irreversible changes in these gratings. The temperature response of slanted transmission gratings was investigated in the temperature range of 20–60 °C. Exposure of the photopolymer layers containing triethanolamine to elevated temperature was found to cause layer shrinkage due to desorption of absorbed water. Sealed layers containing triethanolamine, however, demonstrated swelling due to the effect of thermal expansion. The photopolymer layers containing N -phenylglycine were found to be unresponsive to temperature changes below 30 °C and have sensitivity to temperature above 30 °C.