ALIN MARIAN APETREI | Universitatea Alexandru Ioan Cuza Iasi (original) (raw)
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Page 1. Thèse présentée pour obtenir le grade de DOCTEUR de l'UNIVERSITÉ PARIS XI Spécial... more Page 1. Thèse présentée pour obtenir le grade de DOCTEUR de l'UNIVERSITÉ PARIS XI Spécialité : Optique et Photonique par Alin Marian APETREI ----- Contribution à l'étude de guides à la limite de ...
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Physical Review B, 2013
ABSTRACT An interesting model for spin crossover compounds (SCC) is the so-called spin-phonon cou... more ABSTRACT An interesting model for spin crossover compounds (SCC) is the so-called spin-phonon coupling model. In this model, the SC units are linked by springs, with elastic constants dependent on their spin states. In the present work, we investigate by means of Monte Carlo Metropolis method, the one-dimensional version of the model at T>0 K. The relevance of our numerical analysis stands in the possibility of studying this model in the general case, i.e., outside the analytical limits of the mean-field approximation (MFA). First, we investigate a couple of model properties, such as pressure-induced-like effects on thermal hysteresis loops, system size and degeneracy influences on the dynamic phase diagrams. We find a high sensitivity of the hysteresis loops on the system size for small sizes only. Second, we qualitatively compare our results with those analytically obtained in the MFA and determine the limits of the latter. Third, we study the kinetic effects on the dynamic phase diagrams and the critical temperature. We find a slow asymptotic decrease of the critical temperature Tc to zero as the kinetics becomes infinitely long. This might be important in the experimental studies of pressure-induced phase transitions for clusters or nanosize SC compounds at low temperatures, as this means that, in practice, there will always be a pseudophase transition, as the measurement time is finite. The transition temperatures are smaller than 0.1 Δ/kB, meaning that is not a question of thermal activation, but it is really the mechanism of spin-phonon coupling that helps the transition from the low-spin to the high-spin level state.
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Journal of The Optical Society of America B-optical Physics, 2010
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Applied Physics B-lasers and Optics, 2005
Conventional and scanning near-field optical microscopy techniques are cross referenced to femtos... more Conventional and scanning near-field optical microscopy techniques are cross referenced to femtosecond nonlinear-optical measurements and finite-element numerical simulations to visualize and analyze a strong confinement of electromagnetic radiation in guided modes of a photonic-crystal fiber with only a few air holes surrounding the fiber core. A nonlinear coefficient of about 120 W−1 km−1 is achieved at the wavelength of 670 nm for a fused-silica fiber with a full hexagonal cycle of closely packed air holes around the fiber core. The removal of a single element from this array of air holes is shown to frustrate field confinement in guided modes, leading to mode leakage.
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Optics Express, 2008
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Applied Physics B-lasers and Optics, 2005
We report on the evaluation of a microstructured optical fiber (MOF) designed for non-linear sign... more We report on the evaluation of a microstructured optical fiber (MOF) designed for non-linear signal processing applications, i.e., with a very small guided mode (waist ∼1 μm). Calculations predict an intrinsic (assuming propagation in the fundamental mode and zero-loss coupling) non-linear γ coefficient of 40 W-1 km-1 at λ=1.55 μm, but they also predict a basic multimode character. NSOM measurements validate directly the high intrinsic γ value (32±10 W-1 km-1) and also show that with an optimized coupling, the overall losses in efficiency taking into account coupling losses and weak excitation of higher-order modes and leaky modes are only 2.5 dB. This performance is adequate for use in all-optical data processing lines, all the more since it is maintained for relevant propagation lengths and peak power densities.
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Optics Express, 2005
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IEEE Transactions on Magnetics, 2010
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Physica B-condensed Matter, 2010
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Page 1. Thèse présentée pour obtenir le grade de DOCTEUR de l'UNIVERSITÉ PARIS XI Spécial... more Page 1. Thèse présentée pour obtenir le grade de DOCTEUR de l'UNIVERSITÉ PARIS XI Spécialité : Optique et Photonique par Alin Marian APETREI ----- Contribution à l'étude de guides à la limite de ...
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Physical Review B, 2013
ABSTRACT An interesting model for spin crossover compounds (SCC) is the so-called spin-phonon cou... more ABSTRACT An interesting model for spin crossover compounds (SCC) is the so-called spin-phonon coupling model. In this model, the SC units are linked by springs, with elastic constants dependent on their spin states. In the present work, we investigate by means of Monte Carlo Metropolis method, the one-dimensional version of the model at T>0 K. The relevance of our numerical analysis stands in the possibility of studying this model in the general case, i.e., outside the analytical limits of the mean-field approximation (MFA). First, we investigate a couple of model properties, such as pressure-induced-like effects on thermal hysteresis loops, system size and degeneracy influences on the dynamic phase diagrams. We find a high sensitivity of the hysteresis loops on the system size for small sizes only. Second, we qualitatively compare our results with those analytically obtained in the MFA and determine the limits of the latter. Third, we study the kinetic effects on the dynamic phase diagrams and the critical temperature. We find a slow asymptotic decrease of the critical temperature Tc to zero as the kinetics becomes infinitely long. This might be important in the experimental studies of pressure-induced phase transitions for clusters or nanosize SC compounds at low temperatures, as this means that, in practice, there will always be a pseudophase transition, as the measurement time is finite. The transition temperatures are smaller than 0.1 Δ/kB, meaning that is not a question of thermal activation, but it is really the mechanism of spin-phonon coupling that helps the transition from the low-spin to the high-spin level state.
Bookmarks Related papers MentionsView impact
Journal of The Optical Society of America B-optical Physics, 2010
Bookmarks Related papers MentionsView impact
Applied Physics B-lasers and Optics, 2005
Conventional and scanning near-field optical microscopy techniques are cross referenced to femtos... more Conventional and scanning near-field optical microscopy techniques are cross referenced to femtosecond nonlinear-optical measurements and finite-element numerical simulations to visualize and analyze a strong confinement of electromagnetic radiation in guided modes of a photonic-crystal fiber with only a few air holes surrounding the fiber core. A nonlinear coefficient of about 120 W−1 km−1 is achieved at the wavelength of 670 nm for a fused-silica fiber with a full hexagonal cycle of closely packed air holes around the fiber core. The removal of a single element from this array of air holes is shown to frustrate field confinement in guided modes, leading to mode leakage.
Bookmarks Related papers MentionsView impact
Optics Express, 2008
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Applied Physics B-lasers and Optics, 2005
We report on the evaluation of a microstructured optical fiber (MOF) designed for non-linear sign... more We report on the evaluation of a microstructured optical fiber (MOF) designed for non-linear signal processing applications, i.e., with a very small guided mode (waist ∼1 μm). Calculations predict an intrinsic (assuming propagation in the fundamental mode and zero-loss coupling) non-linear γ coefficient of 40 W-1 km-1 at λ=1.55 μm, but they also predict a basic multimode character. NSOM measurements validate directly the high intrinsic γ value (32±10 W-1 km-1) and also show that with an optimized coupling, the overall losses in efficiency taking into account coupling losses and weak excitation of higher-order modes and leaky modes are only 2.5 dB. This performance is adequate for use in all-optical data processing lines, all the more since it is maintained for relevant propagation lengths and peak power densities.
Bookmarks Related papers MentionsView impact
Optics Express, 2005
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IEEE Transactions on Magnetics, 2010
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Physica B-condensed Matter, 2010
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