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Nonlinear Optics || Nonlinear Optics in the Two-Level Approximation
摘要： Our treatment of nonlinear optics in the previous chapters has for the most part made use of power series expansions to relate the response of a material system to the strength of the applied optical field. In simple cases, this relation can be taken to be of the form ?P (t) = (cid:2)0χ (1) ?E(t) + (cid:2)0χ (2) ?E(t)2 + (cid:2)0χ (3) ?E(t)3 + · · · . However, there are circumstances under which such a power series expansion does not converge, and under such circumstances different methods must be employed to describe nonlinear optical effects. One example is that of a saturable absorber, where the absorption coefficient α is related to the intensity I = 2n(cid:2)0c|E|2 of the applied optical field by the relation α = α0 / (1 + I /Is), where α0 is the weak-field absorption coefficient and Is is an optical constant called the saturation intensity. We can expand this equation in a power series to obtain α = α0 [1 ? (I /Is) + (I /Is)2 ? (I /Is)3 + · · · ]. However, this series converges only for I < Is, and thus only in this limit can saturable absorption be described by means of a power series of the sort given by Eq. (6.1.1).
关键词： Rabi oscillations,two-level approximation,saturable absorber,optical Stark shifts,nonlinear optics
更新于2025-09-23 15:21:01
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[Texts and Readings in Physical Sciences] Open Quantum Systems Volume 20 (Dynamics of Nonclassical Evolution) || Quantum Tunneling
摘要： Tunneling is a bona?de quantum mechanical e?ect [175, 176]. Since it involves barrier penetration, it is also an inherently non-perturbative process. It serves a crucial role in the test of quantum coherence in macroscopic regimes, also known as Macroscopic Quantum Coherence (MQC) [68]. Development in technology has made the concept of tunneling crucial to the development of devices on the nanoscopic, nanometre 10?9m range, and mesoscopic, upto a few microns μm, scales. Further, tunneling has important rami?cations to almost all branches of physics, such as atomic, molecular, condensed matter physics as well as to quantum ?eld theory and cosmology. A very powerful technique for dealing with tunneling is the semiclassical approximation, which we detail below. Tunneling processes can be broadly classi?ed into two categories: coherent and incoherent tunneling. Coherent tunneling phenomena involve the coherent overlap of wavefunctions located in individual domains, such as, ground states of potential wells, and separated by energy barriers. Incoherent tunneling involves scattering between reservoirs or decay of metastable states into the continuum and hence no overlap of the wavefunction. Tunneling has two perspectives: time independent energy domain considerations and that invoking the time dependent dynamics.
关键词： Macroscopic Quantum Coherence,Semiclassical Approximation,Quantum Tunneling,Incoherent Tunneling,Coherent Tunneling
更新于2025-09-23 15:21:01
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-type PbTe from first principles
摘要： We present an ab initio study that identifies the main electron-phonon scattering channels in n-type PbTe. We develop an electronic transport model based on the Boltzmann transport equation within the transport relaxation time approximation, fully parametrized from first-principles calculations that accurately describe the dispersion of the electronic bands near the band gap. Our computed electronic mobility as a function of temperature and carrier concentration is in good agreement with experiments. We show that longitudinal optical phonon scattering dominates electronic transport in n-type PbTe, while acoustic phonon scattering is relatively weak. We find that scattering due to soft transverse optical phonons is by far the weakest scattering mechanism, due to the symmetry-forbidden scattering between the conduction band minima and the zone center soft modes. Soft phonons thus play the key role in the high thermoelectric figure of merit of n-type PbTe: they do not degrade its electronic transport properties although they strongly suppress the lattice thermal conductivity. Our results suggest that materials like PbTe with soft modes that are weakly coupled with the electronic states relevant for transport may be promising candidates for efficient thermoelectric materials.
关键词： electron-phonon scattering,transport relaxation time approximation,thermoelectric materials,Boltzmann transport equation,n-type PbTe
更新于2025-09-23 15:21:01
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Crystallite size and microstrain: XRD line broadening analysis of AgSiN thin films
摘要： Purpose – This paper aims to determine the crystallite size and microstrain values of AgSiN thin films using potential approach called approximation method. This method can be used as a replacement for other determination methods such as Williamson-Hall (W-H) plot and Warren-Averbach analysis. Design/methodology/approach – The monolayer AgSiN thin films on Ti6Al4V alloy were fabricated using magnetron sputtering technique. To evaluate the crystallite size and microstrain values, the thin films were deposited under different bias voltage ((cid:1)75, (cid:1)150 and (cid:1)200 V). X-ray diffraction (XRD) broadening profile along with approximation method were used to determine the crystallite size and microstrain values. The reliability of the method was proved by comparing it with scanning electron microscopy graph and W-H plot method. The second parameters’ microstrain obtained was used to project the residual stress present in the thin films. Further discussion on the thin films was done by relating the residual stress with the adhesion strength and the thickness of the films. Findings – XRD-approximation method results revealed that the crystallite size values obtained from the method were in a good agreement when it is compared with Scherer formula and W-H method. Meanwhile, the calculations for thin films corresponding residual stresses were correlated well with scratch adhesion critical loads with the lowest residual stress was noted for sample with lowest microstrain and has thickest thickness among the three samples. Practical implications – The fabricated thin films were intended to be used in antibacterial applications. Originality/value – Up to the knowledge from literature review, there are no reports on depositing AgSiN on Ti6Al4V alloy via magnetron sputtering to elucidate the crystallite size and microstrain properties using the approximation method.
关键词： AgSiN thin films,XRD-approximation method,Microstrain,Crystallite size
更新于2025-09-23 15:21:01
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Graphite Supported Stainless-Steel Electrode for the Degradation of Azo Dye Orange G by Fenton Reactions: Effect of Photo-Irradiation
摘要： An electrode, stainless steel supported on graphite, was used for the degradation of hazardous organic compounds, azo dye Orange G (OG), using the photoelectro- Fenton (PEF) process. Results showed that the applied current controlled the electrogeneration rate of both ferrous ion and hydrogen peroxide, which in turn affected the dye degradation kinetics. At an applied current density of 45 μA cm?2, the SS-graphite electrode yielded a molar ?H2O2(cid:2)=?Fe2t(cid:2) ratio of 3.6, which was optimal for dye degradation. Under otherwise identical conditions, UV irradiation significantly enhanced OG degradation, i.e., PEF is more effective than electro-Fenton (EF) process. At the optimal applied current density of 45 μA cm?2, or optimal molar ?H2O2(cid:2)=?Fe2t(cid:2) of 3.6, OG decolorization and total organic carbon removal were 83% (in 3 h) and 55% (in 7 h), versus 75% (in 3 h) and 20% (in 7 h) by PEF and EF, respectively. OG degradation by both PEF and EF processes followed the pseudo first-order kinetics, which suggested the major role of OH radical in OG decolorization.
关键词： Stainless steel,Graphite,Orange G,Photo-electro-Fenton (FEF),Steady-state approximation,Decolorization
更新于2025-09-23 15:21:01
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Variation of the oscillator strengths for the <i>α</i> emission lines of the one- and two-electrons ions in dense plasma
摘要： We present the results of a detailed theoretical study on the variation of the oscillator strengths for the 1s ! 2p transition of the H-like ions and the 1s2 1S ! 1s2p 1P transition of the He-like ions (or, inversely, the Lyman-a and Hea emission lines, respectively) subject to external plasma which meet the spatial and temporal criteria of the Debye-H€uckel (DH) approximation. Our study shows that the resulting oscillator strength decreases for the Hea line for He-like ions, similar to the Lyman-a emission lines for all H-like ions, as the effect of the external plasma increases with the decreasing Debye length D in terms of a reduced Debye length kD ? Zeff D. A nearly universal feature is demonstrated for a scaled oscillator strength as a function of the reduced Debye length kD ? (Z (cid:2) 1)D for different He-like ions that meet the same criteria for the DH model. The percentage changes of the oscillator strengths from their plasma-free values are substantially greater than those for the corresponding change for the redshifts of the Lyman-a and Hea emission lines subject to outside dense plasma. Should these general features be demonstrated experimentally, the theoretical procedure presented in this study could easily be applied to extrapolate from a single calculation for one He-like ion to other He-like ions, which could offer an alternative to complement other diagnostic efforts of the dense plasma.
关键词： He-like ions,oscillator strengths,dense plasma,Debye-H€uckel approximation,H-like ions
更新于2025-09-23 15:21:01
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Up-Conversion Luminescence Properties of Lanthanide-Gold Hybrid Nanoparticles as Analyzed with Discrete Dipole Approximation
摘要： Up-conversion nanoparticles (UCNP) under near-infrared (NIR) light irradiation have been well investigated in the field of bio-imaging. However, the low up-conversion luminescence (UCL) intensity limits applications. Plasmonic modulation has been proposed as an effective tool to adjust the luminescence intensity and lifetime. In this study discrete dipole approximation (DDA) was explored concerning guiding the design of UCNP@mSiO2-Au structures with enhanced UCL intensity. The extinction effects of gold shells could be changed by adjusting the distance between the UCNPs and the Au NPs by synthesized tunable mesoporous silica (mSiO2) spacers. Enhanced UCL was obtained under 808 nm irradiation. The original theoretical predictions could not be demonstrated to full extend by experimental data, indicating that better models for simulation need to take into account in homogeneities in particle morphologies. Yet, one very certain conclusion resulting from the DDA calculations and experiments is that the absorbance can blue-shift with more Au NPs added and the absorbance can-red shift for samples with enhanced silica sizes in the UCNP@mSiO2-Au structures. Furthermore, when the DDA model is more consistent with the practical structure (dispersed Au NPs instead of Au shell), the theoretical absorbance occurs almost the same as the practical absorbance. All in all, the DDA could fit the extinction effect of Au perfectly and be suitable for guiding how to design the UCNP and Au.
关键词： lanthanide-based composites,surface plasmon resonance,up conversion nanoparticles,discrete dipole approximation
更新于2025-09-23 15:21:01
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Formation of Quantum Vortices at the Ionization of an Atom by an Ultrashort Laser Pulse: Two- and Three-Dimensional Cases
摘要： Quantum vortices formed at the barrier-suppression ionization of an atom by an ultrashort laser pulse have been studied theoretically and numerically. The ionization of a hydrogen atom is considered in the two-dimensional space and the ionization of an atom in the zero-range potential approximation is considered in the three-dimensional space. The resulting analytical expressions imply that the localization of quantum vortices in the three-dimensional space can be predicted by analyzing the two-dimensional model.
关键词： hydrogen atom,zero-range potential approximation,ultrashort laser pulse,Quantum vortices,barrier-suppression ionization
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Sozopol, Bulgaria (2019.9.6-2019.9.8)] 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Monte Carlo method for analyzing the propagation of radiation in the skin layers containing blood in photoplethysmography
摘要： In evolutionary multiobjective optimization, it is very important to be able to visualize approximations of the Pareto front (called approximation sets) that are found by multi-objective evolutionary algorithms. While scatter plots can be used for visualizing 2-D and 3-D approximation sets, more advanced approaches are needed to handle four or more objectives. This paper presents a comprehensive review of the existing visualization methods used in evolutionary multiobjective optimization, showing their outcomes on two novel 4-D benchmark approximation sets. In addition, a visualization method that uses prosection (projection of a section) to visualize 4-D approximation sets is proposed. The method reproduces the shape, range, and distribution of vectors in the observed approximation sets well and can handle multiple large approximation sets while being robust and computationally inexpensive. Even more importantly, for some vectors, the visualization with prosections preserves the Pareto dominance relation and relative closeness to reference points. The method is analyzed theoretically and demonstrated on several approximation sets.
关键词： projection,evolutionary multiobjective optimization,Pareto front,evolutionary algorithm,visualization,Approximation set
更新于2025-09-23 15:19:57
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Deep inelastic scattering on a nucleus using holography
摘要： We consider deep inelastic scattering (DIS) on a nucleus described using a density expansion. In leading order, the scattering is dominated by the incoherent scattering on individual nucleons distributed using the Thomas-Fermi approximation. We use the holographic structure functions for DIS scattering on single nucleons to make a nonperturbative estimate of the nuclear structure function in leading order in the density. Our results are compared to the fits from data in the large-x regime.
关键词： Thomas-Fermi approximation,deep inelastic scattering,nuclear structure function,holography,nucleus
更新于2025-09-23 15:19:57