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Hot electron thermoreflectance coefficient of gold during electron-phonon nonequilibrium
摘要： The temperature-dependent reflectivity of metals is quantified by the thermoreflectance coefficient, which is a material dependent parameter that depends on the metallic band structure, electron scattering dynamics, and photon wavelength. After short-pulse laser heating, the electronic sub-system in a metal can be driven to temperatures much higher than that of the lattice, which gives rise to unique non-equilibrium electron and phonon scattering dynamics, leading to a “hot electron” thermoreflectance that is different from the traditionally measured equilibrium coefficient. In this work, we analytically quantify and experimentally measure this hot electron thermoreflectance coefficient through ultrafast pump-probe measurements of thin gold films on silica glass and sapphire substrates. We demonstrate the ability to not only quantify the thermoreflectance during electron-phonon nonequilibrium, but also validate this coefficient’s predicted dependence on the absolute temperature of the electronic subsystem. The approach outlined in this work provides a metrology to further understand and quantify excited-state scattering effects on the dielectric function of metals.
关键词： electron-phonon scattering,Pump-probe,Thermoreflectance,Drude model,electronic temperature
更新于2025-09-23 15:21:21
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Generalized local analogue model for nonlocal plasmonic nanostructures based on multiple-fluid hydrodynamic framework
摘要： The control and manipulation of light waves is a long-standing ambition with profound implications for the development of science and technology. Recent advances in nanofabrication allow for a rapid progress in engineering plasmonic nano-devices which collect and concentrate light or electromagnetic waves into a subwavelength region, enabling various applications in nanophotonics, such as bio-sensor with enhanced sensitivity, plasmonic laser, plasmonic colors and quantum plasmonics, to name a few. Spatial dispersion plays a critical role in nanophotonics when small plasmonic structures with feature sizes of few nanometers are handled. Such nonlocality is typically considered in a hydrodynamic framework and generally requires solving coupled partial differential equations, and therefore is involved. We develop a generalized local analogue model to reflect the nonlocal effects of plasmonic structures and avoid the complicated analysis within the multiple-fluid hydrodynamic framework, where more than one kind of charge carriers is considered. We show that spatial nonlocality can be represented by simply replacing the nonlocal surface region with an in-situ artificial local dispersive film. With such an elegant and simple-to-use alternative, the conventional analysis and simulations in the local regime acquire nonlocal capability, sufficient for a quantitative description of various plasmonic structures in nanoscale, rendering a much simpler process and great practical advantages in the numerical treatment.
关键词： multiple fluid,in-situ local model,nonlocal response,hydrodynamic Drude model
更新于2025-09-23 15:21:01
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THz cutoff frequency and multifunction Ti 2Ba2Ca2Cu3O10/GaAs photonic bandgap materials
摘要： By using the transfer matrix method (TMM), we theoretically explore the transmittance properties and cuto? frequency of one-dimensional photonic crystal (1DPCs) within the terahertz frequency region. The present structure consists of high-temperature superconductor and semiconductor layers. The results of the calculations represent the e?ects of various parameters on the cuto? frequency. We have used the two-?uid model as well as the Drude model to describe the permittivity of superconductor and semiconductor. Further, we consider that the permittivity of both the materials is depending on the hydrostatic pressure. The present results show that with the increasing of di?erent parameters as the operating temperature, the thickness of semiconductor, and the ?lling factor of semiconductor, then the cuto? frequency shift to lower frequencies regions. By the increasing of superconductor thickness, hydrostatic pressure, doping concentration and ?lling factor of the superconductor, we found the cuto? frequency shifts to higher frequency regions. These results indicate that cuto? frequency can be modi?ed through these di?erent parameters. Finally, the present design could be useful for many optical systems as the optical ?lter, re?ector and photoelectronic applications in the Terahertz regime.
关键词： Cuto? frequency,transfer matrix method,photonic crystal,doping concentration,hydrostatic pressure,two-?uid model,Drude model
更新于2025-09-23 15:21:01
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Influence of the Nonlocal Effect on the Optical Properties of Nonspherical Plasmonic Semiconductor Nanoparticles
摘要： Noble metals are commonly used as plasmon materials because of their high density of free electrons, but semiconductor materials are also becoming of interesting in this field because its electron density can be varied by doping. Metal nitrides can be an alternative to noble metals because of their low absorption loss and high electron density. Among others, TiN and ZrN seem to be most suitable as alternative plasmonic materials because their optical properties are dominated by conduction electrons near the plasmon frequency. There is the flame spray pyrolysis process, which is currently developed to produce such kind of nanoparticles. In this paper, based on an extension of the discrete sources method, the effect of the hydrodynamic Drude model of the quantum nonlocal effect on the optical characteristics of semiconductor nanoparticles is analyzed. The influence of accounting for the nonlocal effect (NLE) on the optical properties under spherical particles deformation has been investigated. It has been shown that accounting for the NLE leads to a plasmon resonance blue shift and a damping similar to noble metals. It was found that smaller particles demonstrate larger NLE influence than larger ones. Besides, the influence of polarization on the local and nonlocal responses of 3D nonspherical semiconductor particles has been investigated as well. Using simulation accounting for the nonlocal effect, it is shown that the extinction of a nonspherical ZrN particles exceeds that of a gold particle.
关键词： discrete sources method,nonlocal effect,hydrodynamic Drude model,nonspherical semiconductor nanoparticle,plasmonics,Light scattering
更新于2025-09-23 15:21:01
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Nonlinear Optics || Nonlinear Optics of Plasmonic Systems
摘要： In the present chapter we explore the optical properties of plasmonic systems. The word plasmonics is often associated with the properties of metals. The reason for this association is that both the electrical and optical properties of metals are intimately related to the large number of nearly free electrons present in the conduction band of a metal. In this chapter we will primarily be concerned with the optical properties of metals, although the fundamental results that we obtain equally well describe the optical properties of other types of plasmas. The properties of nearly free electrons have been described earlier in this book, for instance as a limiting case of the Lorentz model described in Section 1.4 and also in terms of relativistic effects of plasmas as described in Section 13.7. The present chapter seeks to describe the properties of plasmonic systems in a cohesive manner. Part of the reason for interest in plasmonic systems is that they display very strong light-matter coupling, and this strong coupling leads to both linear and nonlinear properties that can be qualitatively different from those of nonplasmonic systems. This coupling leads for example to a propagating wave, known as a surface plasmon polariton (SPP), which is a mixed excitation of both electron and electromagnetic ?eld oscillations. Plasmonic systems also tend to display large nonlinear optical effects, both because metals often possess a large value ofχ (3) and because for the case of composite systems electric ?elds tend to become enhanced in regions near a metallic particle. More detailed accounts of the the role of plasmonics in nonlinear optics can be found in the accounts of Kauranen and Zayats (2012), Maier (2007), and Novotny and Hecht (2006a).
关键词： surface plasmon polariton,Drude model,plasmonics,gold,nonlinear optics
更新于2025-09-23 15:21:01
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Plasmon enhanced second harmonic generation by periodic arrays of triangular nanoholes coupled to quantum emitters
摘要： Optical properties of periodic arrays of nanoholes of a triangular shape with experimentally realizable parameters are examined in both linear and nonlinear regimes. By utilizing a fully vectorial three-dimensional approach based on the nonlinear hydrodynamic Drude model describing metal coupled to Maxwell’s equations and Bloch equations for molecular emitters, we analyze linear transmission, reflection, and nonlinear power spectra. Rigorous numerical calculations demonstrating second and third harmonic generation by the triangular hole arrays are performed. It is shown that both the Coulomb interaction of conduction electrons and the convective term contribute on equal footing to the nonlinear response of metal. It is demonstrated that the energy conversion efficiency in the second harmonic process is the highest when the system is pumped at the localized surface plasmon resonance. When molecular emitters are placed on a surface of the hole array line shapes, the second harmonic signal exhibits three peaks corresponding to second harmonics of the localized surface plasmon mode and upper and lower polaritonic states.
关键词： strong coupling,second harmonic generation,hydrodynamic Drude model,plasmonics,nonlinear optics
更新于2025-09-19 17:13:59
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Fundamentals and Applications of Nanophotonics || A dynamical, classical oscillator model for linear and nonlinear optics
摘要： In this chapter we will build and develop a self-consistent, classical oscillator model to describe linear and nonlinear optical interactions like refraction and frequency conversion in both centrosymmetric and noncentrosymmetric materials. In addition to being quite ubiquitous in all of physics, the classical oscillator model of matter is an enormously pedagogical tool that serves as a natural springboard to the description and understanding of quantum systems and leads to a rather detailed portrayal of all the dynamical factors that contribute to most linear and nonlinear optical phenomena. The method is endowed with causality as well as a natural degree of self-consistency that includes linear and nonlinear material dispersions, elements that are usually necessary to understand many of the subtleties of the interaction of light with matter. By way of examples, using this classical approach we will examine harmonic generation in bulk materials and in metal-based nanostructures. In centrosymmetric materials like metals (materials composed of molecules that lack a center of symmetry), second harmonic generation (SHG) arises mostly from nearly free, conduction electrons (nearly free because they are con?ned by the metal walls) and is due to a combination of spatial symmetry breaking (interfaces), the magnetic portion of the Lorentz force, and, to a lesser extent, the interaction of third harmonic (TH) and pump photons. By the same token, the third order nonlinearity (c(3)) gives rise to most of the TH signal, while to a small degree the interaction of pump and SH photons also produces cascaded, TH photons. The classical oscillator model will be pivotal in these systems as well, where a combination of free (Drude) and bound (Lorentz) electrons suf?ces to describe most linear and nonlinear optical phenomena.
关键词： Lorentz model,centrosymmetric materials,noncentrosymmetric materials,classical oscillator model,harmonic generation,linear and nonlinear optics,Drude model
更新于2025-09-16 10:30:52
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Modal analysis for nanoplasmonics with nonlocal material properties
摘要： Plasmonic devices with feature sizes of a few nanometers exhibit effects which can be described by the nonlocal hydrodynamic Drude model. We demonstrate how to exploit contour integral methods for computing eigenfrequencies and resonant states of such systems. We propose an approach for deriving the modal expansion of relevant physical observables. We use the methods to perform a modal analysis for a metal nanowire. All complex eigenfrequencies in a large frequency range and the corresponding resonant states are computed. We identify those resonant states which are relevant for the extinction cross section of the nanowire.
关键词： extinction cross section,nanoplasmonics,hydrodynamic Drude model,modal analysis,nonlocal material properties,metal nanowire
更新于2025-09-16 10:30:52
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Ultrafast Plasmon Dynamics and Hole–Phonon Coupling in NIR Active Nonstoichiometric Semiconductor Plasmonic Cu <sub/> 2– <i>x</i> </sub> S Nanocrystals
摘要： Nonstoichiometric Cu2?xS nanocrystals (NCs) have been synthesized by hot-injection method after changing the copper to sulfur ratio. Optical studies confirmed well-defined localized surface plasmon resonance (LSPR) absorbance band from near-infrared to mid-infrared arising due to p-type hole vacancy in the doped semiconductor. Carrier concentrations of the Cu2?xS NCs are calculated to be on the order of ～1021 cm?3 after following the Drude model, which is one order of magnitude lower as compared to the metallic (Au/Ag) system. To understand ultrafast plasmon dynamics of Cu2?xS NCs, femtosecond broadband (visible?near IR) pump?probe spectroscopy has been employed. Ultrafast plasmon dynamics of the Cu2?xS NCs have been monitored after changing composition (copper to sulfur ratio), pump wavelength, and laser intensity. At moderate pump power hole?phonon relaxation time constant has been observed to be in the range of 240?440 fs for Cu2?xS NCs depending upon pump wavelengths (400, 800 nm). From the ultrafast transient data, hole?phonon coupling constant (G) has been determined in the range (1.6?2.7) × 1010 J K?1 s?1 cm?3 for Cu2?xS NCs at different excitation wavelengths, which is also one order lower as compared to the metallic system. We have proposed a new mechanistic scheme for hot carrier relaxation dynamics, in accordance with the two-temperature model (TTL) as reported in literature for plasmon dynamics.
关键词： Nonstoichiometric Cu2?xS nanocrystals,femtosecond broadband pump?probe spectroscopy,localized surface plasmon resonance,hole?phonon coupling constant,two-temperature model,Drude model
更新于2025-09-12 10:27:22
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Reconstructing charge-carrier dynamics in porous silicon membranes from time-resolved interferometric measurements
摘要： We performed interferometric time-resolved simultaneous reflectance and transmittance measurements to investigate the carrier dynamics in pump-probe experiments on thin porous silicon membranes. The experimental data was analysed by using a method built on the Wentzel-Kramers-Brillouin approximation and the Drude model, allowing us to reconstruct the excited carriers’ non-uniform distribution in space and its evolution in time. The analysis revealed that the carrier dynamics in porous silicon, with ~50% porosity and native oxide chemistry, is governed by the Shockley-Read-Hall recombination process with a characteristic time constant of 375 picoseconds, whereas diffusion makes an insignificant contribution as it is suppressed by the high rate of scattering.
关键词： carrier dynamics,porous silicon,Drude model,Shockley-Read-Hall recombination,interferometric measurements
更新于2025-09-11 14:15:04