- 标题
- 摘要
- 关键词
- 实验方案
- 产品
过滤筛选
- 2019
- photovoltaic power generation system
- sensitivity analysis
- Monte Carlo
- fuzzy layering evaluation method
- Electrical Engineering and Automation
- Xi’an Jiaotong University
-
Circular dichroism & isotropy - polarity Reversal of Ellipticity in molecular films of 1,1’-Bi-2-Naphtol
摘要： We have studied the circular dichroism (CD) in the ultra violet and visible region of the transparent, chiral molecule 1,1’-Bi-2-Naphtol (BINOL) in 1.5 μm thick films. The initial transparent film shows an additional negative cotton effect in the CD compared to solution. With time under room temperature the film undergoes a structural phase transition. This goes hand in hand with a cotton effect at the low energy absorption band which inverts with opposite propagation direction of light through the film which is revealed as a polarity reversal of ellipticity (PRE). After completion of the phase transition the film exhibits circular differential scattering throughout the visible range which also shows PRE. The structure change was studied with Raman, microscopy under cross polarization conditions and nonlinear second-harmonic generation circular dichroism (SHG-CD). The superposition of the optical activity of individual molecules and isotropy effects makes an interpretation challenging. Yet overcoming this challenge by finding a suitable model structural information can be derived from CD measurements.
关键词： Second-harmonic generation circular dichroism,Isotropy,Polarity reversal of ellipticity,Circular dichroism
更新于2025-09-10 09:29:36
-
Time-resolved second harmonic generation with single-shot phase sensitivity
摘要： A time-resolved, phase-sensitive second harmonic generation (SHG) method to probe the excited state dynamics of interfacial species is presented. It is based on an interference measurement between the SHG from a sample and a local oscillator generated at a reference surface in which an entire interference pattern is recorded in a single shot by using a spatially varying phase unit comprised of a pair of wedges that sandwich the reference sample. In combination with 30 kHz modulation of the experiment, shot-to-shot pump-probe measurements are presented. The technique is characterised by measuring the time-resolved change in the amplitude and phase of the interference pattern due to the excited state dynamics of the dye malachite green at the air/water interface. The key attributes of the technique are its excellent phase stability and sensitivity, and relatively short data acquisition times.
关键词： air/water interface,excited state dynamics,time-resolved,second harmonic generation,malachite green,phase-sensitive,interference measurement
更新于2025-09-09 09:28:46
-
[IEEE 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Espoo, Finland (2018.8.27-2018.9.1)] 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Nonlinear Quasi-Phase Matching with metasurfaces
摘要： Quasi-Phase Matching is an optical process needed to build up nonlinear signal from strong pump intensity and is generally obtained through periodical inversion of coherence domains of the crystal. We show that this effect can be arti?cially monitored through inserting metasurfaces along the optical path of the light in a waveguide. Sub-wavelength gratings of holes are etched in Gallium Nitride to locally change medium dispersion, allowing continuous increase of the second harmonic signal. This approach can be used to address any phase delay difference between pump and signal at will, not only π, opening up new perspectives for arbitrary phase matching conditions. It can also be implemented in highly nonlinear systems, in which it is generally hard to address phase-matching conditions, for instance waveguides with buried intersubband quantum wells or other materials such GaAs.
关键词： second harmonic generation,metasurfaces,Quasi-Phase Matching,Gallium Nitride,nonlinear optics
更新于2025-09-09 09:28:46
-
Analysis of Second-Harmonic Generation of Low-Frequency Dilatational Lamb Waves in a Two-Layered Composite Plate
摘要： We analyze the effect of second-harmonic generation (SHG) of primary Lamb wave propagation in a two-layered composite plate, and then investigate the influence of interfacial properties on the said effect at low frequency. It is found that changes in the interfacial properties essentially affect the dispersion relation and then the maximum cumulative distance of the double-frequency Lamb wave generated. This will remarkably influence the efficiency of SHG. To overcome the complications arising from the inherent dispersion and multimode natures in analyzing the SHG effect of Lamb waves, the present work focuses on the analysis of the SHG effect of low-frequency dilatational Lamb wave propagation. Both the numerical analysis and finite element simulation indicate that the SHG effect of low-frequency dilatational Lamb wave propagation is found to be much more sensitive to changes in the interfacial properties than primary Lamb waves. The potential of using the SHG effect of low-frequency dilatational Lamb waves to characterize a minor change in the interfacial properties is analyzed.
关键词： composite plate,interfacial properties,low frequency,second-harmonic generation,Lamb waves
更新于2025-09-09 09:28:46
-
On harmonic injection anti-islanding techniques under the operation of multiple DER-inverters
摘要： This work studies the impact of multiple Distributed-Energy-Resource (DER) inverters (which are connected to the same node) on anti-islanding protection of DER-installations. As it concerns the harmonic injection-based schemes, the induced harmonic voltage component that is provoked by each inverter is compromised, as synchronous injection (injection at the same time intervals) among the inverters cannot be reassured. Therefore, harmonic injection-based anti-islanding schemes will fail if the harmonic voltage component falls below a certain level. In this framework, a novel metric (i.e. the Upgrade-Factor, UF) is introduced, indicating the supplementary power (of DERs) that can be installed in the same point of common coupling without compromising the effectiveness of the harmonic injection scheme. As this metric enables the evaluation of harmonic injection schemes prior to the future integration of DERs, it could be a substantial addendum into the relevant standards that evaluates the anti-islanding features of grid-tied DER-inverters. Finally, this work proposes a technique (implemented in software level), which maximizes UF and reassures the effectiveness of the harmonic injection schemes under the power variations of installed inverters. Extensive simulations and experimental tests have been conducted that verify the effectiveness of the proposed strategy under various penetration-levels and islanding-network conditions.
关键词： Anti-Islanding,Multiple Distributed Generation Systems,Distributed Energy Resources,High penetration
更新于2025-09-09 09:28:46
-
Photoconductive antennas based on epitaxial films In <sub/>0.5</sub> Ga <sub/>0.5</sub> As on GaAs (1?1?1)A and (1?0?0)A substrates with a metamorphic buffer
摘要： The terahertz (THz) wave generation by the spiral photoconductive antennas fabricated on the low-temperature and high-temperature grown undoped and Si-doped In0.5Ga0.5As films is studied by the terahertz time-domain spectroscopy method. The In0.5Ga0.5As layers were grown by molecular beam epitaxy on GaAs substrates with (1 0 0) and (1 1 1) A crystallographic orientations utilizing step-graded InxGa1?xAs metamorphic buffer. The antennas are excited by radiation of Er3+-fiber laser at 1.56 μm wavelength in two regimes: with pulse durations of 2.5 ps or 100 fs. It is found that the THz wave generation is 3–4 times more effective in the case of InGaAs-based antennas on (1 1 1)A GaAs substrates as compared to the (1 0 0) substrates. Power-voltage characteristic of the LT-InGaAs antenna up to and beyond threshold breakdown voltage are reported.
关键词： time-domain spectroscopy,terahertz wave generation,photoconductive antenna,GaAs (1 1 1)A,InGaAs,molecular beam epitaxy
更新于2025-09-09 09:28:46
-
Nonlinear optical susceptibility of atomically thin WX2 crystals
摘要： We have studied tungsten diselenide (WSe2) and tungsten disulfide (WS2) monolayer materials in second harmonic generation spectroscopy and microscopy experiments. Ultra-broadband continuum pulses served as the fundamental beam while its second harmonic spectrum in the visible and ultraviolet (UV) range was detected and analyzed with a better than 0.3 nm spectral resolution (< 2 meV). We provide dispersion data and absolute values for χ(2) for the materials within a photon energy range of 2.3–3.2 eV. Fine spectral features that were detected within the dispersion data for the optical nonlinearities indicate the impact of near bandgap exciton transitions. The fundamental bandgap of 2.35 eV and exciton binding energy of 0.38 eV were determined from the measurements for WS2 monolayers while the corresponding values in WSe2 monolayers were 2.22 eV and 0.71 eV. Ranges for the absolute values of the sheet nonlinearity for WS2 and WSe2 are shown to be 0.58–1.65 × 10?18 m2/V and 0.21–0.92 × 10?18 m2/V, correspondingly.
关键词： Nonlinear spectroscopy and microscopy,Transition metal dichalcogenides,Two-dimensional semiconductors,Second harmonic generation,Optical nonlinearity in semiconductors,Monolayer crystals,Optics at interfaces
更新于2025-09-09 09:28:46
-
A polaron approach to photorefractivity in Fe : LiNbO<sub>3</sub>
摘要： The thermally activated, incoherent hopping of small electron polarons generated by continuous illumination in iron-doped lithium niobate is simulated by a Marcus-Holstein model for which all the input parameters are known from literature. The results of the calculations are compared with a comprehensive set of data obtained from photorefractive, photogalvanic and photoconductive measurements under green light excitation on samples with different doping levels and stoichiometries and composition dependence of the photorefractive observables can be interpreted by a change in the abundance of the different hop types that a polaron performs before being captured by a deep Fe trap. Moreover, by a comparison between experimental and numerical data we obtain new insights on the initial photo-excitation part of the photorefractive process. In particular all results are consistent if a single value of the photogalvanic length LP G = (1.44 ± 0.05) ? is assumed for all the samples and all the temperatures. The photo-generation efficiency φ under green light excitation (somewhere denoted as quantum efficiency) is also estimated. It appears to decrease from 10-15% at room temperature to about 5% at 150K. This behavior is qualitatively interpreted in terms of a temperature-dependent re-trapping probability of the light-emitted particles from the initial Fe donor center.
关键词： photo-generation efficiency,polaron,photogalvanic length,Fe:LiNbO3,Marcus-Holstein model,photorefractivity
更新于2025-09-09 09:28:46
-
A gauge-invariant formulation of interband and intraband currents in solids
摘要： Experiments and simulations in solid-state high harmonic generation often make use of the distinction between interband and intraband currents. These two contributions to the total current have been associated with qualitatively different processes as well as physically measurable signatures, for example, in the spectral phase of harmonic emission. However, it was recently argued [P. F?ldi, Phys. Rev. B 96, 035112 (2017)] that these quantities can depend on the gauge employed in calculations. Since physical quantities are expected to have gauge-independent values, this raises the question of whether the decomposition of the total current into interband and intraband contributions is physically meaningful or merely a feature of a particular mathematical representation of nature. In this article, we explore this apparent ambiguity. We show that a closely related issue arises when calculating instantaneous band populations. In both the case of inter/intraband currents and the case of instantaneous band populations, we propose definitions that are gauge invariant and thus allow these quantities to be calculated consistently in any gauge.
关键词： gauge invariance,solid-state,interband currents,band populations,intraband currents,high harmonic generation
更新于2025-09-09 09:28:46
-
Supercontinuum manipulation based on the influence of chirp on soliton spectral tunneling
摘要： The soliton spectral tunneling (SST) effect, as a soliton spectral switching phenomenon, enables a soliton to tunnel through a spectrally limited regime of normal dispersion in the fiber with multiple zero dispersion wavelengths (ZDWs). Since initial chirp can affect the behavior of pulse evolution, we numerically study the influence of chirp on the SST in the process of supercontinuum (SC) occurring in a photonic crystal fiber (PCF) with three ZDWs. The linear chirp is imposed by a phase modulation of input pulse while maintaining a constant pulse duration. Interestingly, it is found that the spectral range and flatness can be flexibly tuned by adjusting the initial chirp value. More specifically, positive chirp facilitates soliton self-frequency shifting (SSFS), making the soliton quickly transfer from one anomalous dispersion regime to another accompanied by the generation of dispersive waves (DWs). In this case, the SST effect further expands the spectral range by enhancing both the red-shift of the fundamental soliton and the blue-shift of DWs, thus generating a broader SC. However, negative chirp suppresses the SST effect, resulting in a smoother SC at the expense of bandwidth. Therefore, the findings in this work provide interesting results relating to the influence of initial chirp on the SST to generate a considerably smoother and broader SC, which is extremely useful in many applications, such as wavelength conversion and SC generation.
关键词： soliton spectral tunneling,chirp,supercontinuum generation
更新于2025-09-09 09:28:46