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Optical diffraction radiation from a dielectric and a metal nanowire excited by a modulated electron beam
摘要： The optical diffraction radiation that accompanies the motion of a modulated beam of electrons near a dielectric and silver nanowire scatterers is investigated in the two-dimensional formulation. Our goal is to compute the field in the near and far zones and analyze how it depends on electron beam parameters. We demonstrate the excitation of internal resonances of such a scatterer that can be useful in the design of nanoscale non-invasive beam position monitors.
关键词： Plasmon resonance,Diffraction radiation,Nanowire scatterers,Total scattering cross-section,Absorption cross-section,Smith–Purcell effect,Surface wave
更新于2025-09-23 15:22:29
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Changes of the absorption cross section of Si nanocrystals with temperature and distance
摘要： The absorption cross section (ACS) of silicon nanocrystals (Si NCs) in single-layer and multilayer structures with variable thickness of oxide barriers is determined via a photoluminescence (PL) modulation technique that is based on the analysis of excitation intensity-dependent PL kinetics under modulated pumping. We clearly demonstrate that roughly doubling the barrier thickness (from ca. 1 to 2.2 nm) induces a decrease of the ACS by a factor of 1.5. An optimum separation barrier thickness of ca. 1.6 nm is calculated to maximize the PL intensity yield. This large variation of ACS values with barrier thickness is attributed to a modulation of either defect population states or of the efficiency of energy transfer between confined NC layers. An exponential decrease of the ACS with decreasing temperature down to 120 K can be explained by smaller occupation number of phonons and expansion of the band gap of Si NCs at low temperatures. This study clearly shows that the ACS of Si NCs cannot be considered as independent on experimental conditions and sample parameters.
关键词： silicon nanocrystals,average lifetime,absorption cross section,photoluminescence decay,nanocrystal distance
更新于2025-09-23 15:22:29
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On the determination of absorption cross section of colloidal lead halide perovskite quantum dots
摘要： The absorption cross section of lead halide perovskite nanocrystals is important for understanding their photophysical properties, especially those depending on the density of photoexcited charge carriers. Despite its importance, there are large discrepancies among the reported absorption cross section values determined employing different methods. Here, we measured the absorption cross section of CsPbBr3 quantum dots (QDs) of varying sizes using elemental analysis and transient absorption (TA) saturation methods and compared with the previously reported values determined from elemental analysis and transient photoluminescence (PL) saturation methods. A careful comparison indicates that the reliable absorption cross section of lead halide perovskite QDs is obtained from both elemental analysis and TA saturation methods, while many previously reported values determined from the PL saturation method underestimate the absorption cross section.
关键词： quantum dots,absorption cross section,photoluminescence,transient absorption,lead halide perovskite
更新于2025-09-23 15:19:57
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Nanoplasma properties in metallic clusters driven by a Gaussian laser beam in the presence of helical magnetic undulator
摘要： The motivation of present paper is the investigation of effective permittivity and absorption cross section of cluster nanoplasmas in the interaction of a Gaussian laser beam with a cluster of metallic nanoparticles, in the presence of a helical magnetic undulator. The static magnetic field of the undulator couples with the field of the laser wave, and forms a nonlinear force in the interaction region. As a result, the nonlinear force varies the plasmonic oscillations of the electron of nanoplasmas that leads to electron density modulation, which modifies absorption cross section and effective permittivity of nanoparticles. Using a perturbative method, we analytically derived the nonlinear dispersion waves and dielectric constant of metallic nanoparticles lattice (gold, silver, and copper) in the presence of a helical magnetic undulator. Numerical results indicate that with increasing the undulator magnetic field strength, absorption cross section of cluster nanoplasmas increases and absorption phenomenon occurs at frequencies close to the effective plasma frequency. Besides, with decreasing distance of nanoparticles in the cluster (and with increasing the nanoparticles radius), absorption cross section increases. We also found that the dielectric constant of the cluster nanoplasma medium increases with enhancing undulator magnetic field strength only near the effective plasmonic frequency. This concept opens a path toward new properties of cluster nanoplasmas as quantum dots, diagnostics, and sensors based on magnetic undulator structures.
关键词： Gaussian laser beam,Effective permittivity,Metallic clusters,Nanoplasma,Absorption cross section,Helical magnetic undulator
更新于2025-09-19 17:13:59
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Nonlinear absorption and scattering of a single plasmonic nanostructure characterized by <i>x</i> -scan technique
摘要： Nonlinear nanoplasmonics is a largely unexplored research area that paves the way for many exciting applications, such as nanolasers, nanoantennas, and nanomodulators. In the field of nonlinear nanoplasmonics, it is highly desirable to characterize the nonlinearity of the optical absorption and scattering of single nanostructures. Currently, the common method to quantify optical nonlinearity is the z-scan technique, which yields real and imaginary parts of the permittivity by moving a thin sample with a laser beam. However, z-scan typically works with thin films, and thus acquires nonlinear responses from ensembles of nanostructures, not from single ones. In this work, we present an x-scan technique that is based on a confocal laser scanning microscope equipped with forward and backward detectors. The two-channel detection offers the simultaneous quantification for the nonlinear behavior of scattering, absorption and total attenuation by a single nanostructure. At low excitation intensities, both scattering and absorption responses are linear, thus confirming the linearity of the detection system. At high excitation intensities, we found that the nonlinear response can be derived directly from the point spread function of the x-scan images. Exceptionally large nonlinearities of both scattering and absorption are unraveled simultaneously for the first time. The present study not only provides a novel method for characterizing nonlinearity of a single nanostructure, but also reports surprisingly large plasmonic nonlinearities.
关键词： nonlinear absorption,absorption cross section,nonlinear scattering,single gold nanostructures,laser scanning microscopy,nanoplasmonics
更新于2025-09-16 10:30:52
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Visible light from modulated electron beam moving between twin circular silver nanowires forming plasmonic photonic molecule
摘要： The visible-range diffraction radiation of harmonically modulated electron beam, which moves between twin circular silver nanowires is considered. The electromagnetic field of such a two-dimensional beam is a surface wave propagating along its trajectory with the phase velocity equal to the beam velocity. This wave induces currents on the nanowires and hence radiation occurs even if the beam does not touch the wires. If the wires are tuned to a resonance, the radiated power displays a peak proportional to the resonant mode Q-factor. Sub-wavelength in radius silver nanowires are famous as nanoresonators due to the localized surface-plasmon modes. In our analysis, we use the field expansions in the azimuthal Fourier series and the addition theorems for the cylindrical functions. This enables us to reduce the wave scattering problem to a Fredholm second kind infinite-matrix equation that guarantees convergence of numerical solutions. Truncating this matrix, we compute the near and far field patterns of the wires as optically coupled plasmonic resonators and analyse dependence of the far-field spectral characteristics on the wavelength and electron beam parameters.
关键词： absorption cross-section,optical diffraction radiation,total scattering cross-section,plasmon resonance,surface wave,silver nanowires
更新于2025-09-12 10:27:22
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[IEEE 2018 XXIIIrd International Seminar/Workshop on Direct and Inverse Problems of Electromagnetic and Acoustic Wave Theory (DIPED) - Tbilisi, Georgia (2018.9.24-2018.9.27)] 2018 XXIIIrd International Seminar/Workshop on Direct and Inverse Problems of Electromagnetic and Acoustic Wave Theory (DIPED) - Optical Diffraction Radiation of a Beam of Particles Flowing Near a Circular Silver Nanowire
摘要： The optical diffraction radiation that accompanies the motion of a modulated beam of electrons near a silver nanowire scatterer is investigated in the two-dimensional formulation. Our goal is to compute the field in the near and far zones and analyze how it depends on electron beam parameters. We demonstrate the excitation of plasmon resonances of such a nanoscale scatterer that can be used in the design of optical range non-invasive beam position monitors.
关键词： plasmon resonance,diffraction radiation,surface wave,total scattering cross-section,nanowire scatterers,absorption cross-section
更新于2025-09-10 09:29:36
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Research on Measurement Uncertainty of Absorption Cross Section in a Reverberation Chamber
摘要： The absorption cross section (ACS) of absorbers are measured in a reverberation chamber and the relative uncertainty of measurements is calculated. The ACS is calculated by a time-domain method at frequencies in the range 1~3GHz. The average relative uncertainty of the ACS over the frequency range in eight different configurations of absorbers and antennas, which shows good experimental stability, is 0.02 by the measurements.
关键词： Time-domain Method,Absorbers,Reverberation Chamber,Measurement Uncertainty,Absorption Cross Section
更新于2025-09-10 09:29:36
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Transition rate and the photoelectric effect in the presence of a minimal length
摘要： In this work, according to the generalized uncertainty principle (GUP) and time-dependent perturbation theory, the transition rate in the present of a minimal length based on the Kempf algebra is studied. Also, we ?nd the absorption cross section in the framework of the GUP. The modi?ed photoelectric effect is investigated and we show that the differential cross section of the photoelectric effect in the framework of the GUP is related to the isotropic minimal length scale. The upper bound on the isotropic minimal length is estimated.
关键词： absorption cross section,minimal length,generalized uncertainty principle,transition rate,photoelectric effect
更新于2025-09-04 15:30:14