- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Quench dynamics of finite bosonic ensembles in optical lattices with spatially modulated interactions
摘要： The nonequilibrium quantum dynamics of few boson ensembles which experience a spatially modulated interaction strength and are confined in finite optical lattices is investigated. We utilize a cosinusoidal spatially modulated effective interaction strength which is characterized by its wavevector, inhomogeneity amplitude, interaction offset and a phase. Performing quenches either on the wavevector or the phase of the interaction profile an enhanced imbalance of the interatomic repulsion between distinct spatial regions of the lattice is induced. Following both quench protocols triggers various tunneling channels and a rich excitation dynamics consisting of a breathing and a cradle mode. All modes are shown to be amplified for increasing inhomogeneity amplitude of the interaction strength. Especially the phase quench induces a directional transport enabling us to discern energetically, otherwise, degenerate tunneling pathways. Moreover, a periodic population transfer between distinct momenta for quenches of increasing wavevector is observed, while a directed occupation of higher momenta can be achieved following a phase quench. Finally, during the evolution regions of partial coherence are revealed between the predominantly occupied wells.
关键词： nonequilibrium dynamics,spatially dependent interactions,excited states,few-body systems,quench dynamics,optical lattices
更新于2025-09-23 15:21:01
-
Theoretical study of Da??Aa?2a????a??A/Da????a??Aa?2a????a??A triphenylamine and quinoline derivatives as sensitizers for dye-sensitized solar cells
摘要： We have designed four dyes based on D–A0–p–A/D–p–A0–p–A triphenylamine and quinoline derivatives for dye-sensitized solar cells (DSSCs) and studied their optoelectronic properties as well as the e?ects of the introduction of alkoxy groups and thiophene group on these properties. The geometries, single point energy, charge population, electrostatic potential (ESP) distribution, dipole moments, frontier molecular orbitals (FMOs) and HOMO–LUMO energy gaps of the dyes were discussed to study the electronic properties of dyes based on density functional theory (DFT). And the absorption spectra, light harvesting e?ciency (LHE), hole–electron distribution, charge transfer amount from HOMO to LUMO (QCT), D index, HCT index, Sm index and exciton binding energy (Ecoul) were discussed to investigate the optical and charge-transfer properties of dyes by time-dependent density functional theory (TD-DFT). The calculated results show that all the dyes follow the energy level matching principle and have broadened absorption bands at visible region. Besides, the introduction of alkoxy groups into triarylamine donors and thiophene groups into conjugated bridges can obviously improve the stability and optoelectronic properties of dyes. It is shown that the dye D4, which has had alkoxy groups as well as thiophene groups introduced and possesses a D–p–A0–p–A con?guration, has the optimal optoelectronic properties and can be used as an ideal dye sensitizer.
关键词： alkoxy groups,thiophene group,density functional theory,dye-sensitized solar cells,D–A0–p–A/D–p–A0–p–A,triphenylamine,quinoline derivatives,time-dependent density functional theory,optoelectronic properties
更新于2025-09-23 15:21:01
-
Luminescence Line Broadening of CdSe Nanoplatelets and Quantum Dots for Application in w-LEDs
摘要： Nanoplatelets (NPLs) of CdSe are an emerging class of luminescent materials, combining tunable and narrow emission bands with high quantum yields. This is promising for application in white light LEDs (w-LEDs) and displays. The origin of the narrow spectral width of exciton emission in core NPL compared to core-shell NPL and quantum dot (QD) emission is not fully understood. Here we investigate and compare temperature dependent emission spectra of core and core-shell CdSe NPLs and QDs. A wide temperature range, 4 to 423 K, is chosen to gain insight in contributions from homogeneous and inhomogeneous broadening and also to extend measurements into a temperature regime that is relevant for operating conditions in w-LEDs (T~423 K). The results show that temperature induced homogeneous broadening does not strongly vary between the various CdSe nanostructures (ΔEhom≈60-80 meV at 423 K) indicating that electron-phonon coupling strengths are similar. Only for the smallest QDs stronger coupling is observed. The origin of the narrow bandwidth reported at 300 K for core CdSe NPLs is attributed to a very narrow inhomogeneous linewidth. At 423 K the spectral width of NPL exciton emission is still superior to that of QDs. A comparison with traditional w-LED phosphors is made to outline advantages (tunability, narrow bandwidth, high efficiency) and disadvantages (color shift, stability issues) of NPLs for application in w-LEDs.
关键词： w-LEDs,Quantum Dots,Temperature dependent emission spectra,CdSe Nanoplatelets,Luminescence
更新于2025-09-23 15:21:01
-
Nonlinear Optics || The Intensity-Dependent Refractive Index
摘要： The refractive index of many optical materials depends on the intensity of the light used to measure the refractive index. In this chapter, we examine some of the mathematical descriptions of the nonlinear refractive index and examine some of the physical processes that give rise to this effect. In the following chapter, we study the origin of optical nonlinearities in molecular systems, in Chapter 6 we study the intensity-dependent refractive index resulting from the resonance response of an atomic system, and in Chapter 7 we study some physical processes that result from the nonlinear refractive index.
关键词： intensity-dependent,atomic system,optical materials,nonlinear refractive index,molecular systems
更新于2025-09-23 15:21:01
-
Nonlinear Optics || Molecular Origin of the Nonlinear Optical Response
摘要： In Chapter 3, we presented a general quantum-mechanical theory of the nonlinear optical susceptibility. This calculation was based on time-dependent perturbation theory and led to explicit predictions for the complete frequency dependence of the linear and nonlinear optical susceptibilities. Unfortunately, however, these quantum-mechanical expressions are typically far too complicated to be of use for practical calculations. In this chapter we review some of the simpler approaches that have been implemented to develop an understanding of the nonlinear optical characteristics of various materials. Many of these approaches are based on understanding the optical properties at the molecular level. We also present brief descriptions of the nonlinear optical characteristics of conjugated polymers, chiral molecules, and liquid crystals.
关键词： chiral molecules,nonlinear optical susceptibility,liquid crystals,quantum-mechanical theory,conjugated polymers,time-dependent perturbation theory
更新于2025-09-23 15:21:01
-
Faceta??Dependent, Fast Response, and Broadband Photodetector Based on Highly Stable Alla??Inorganic CsCu <sub/>2</sub> I <sub/>3</sub> Single Crystal with 1D Electronic Structure
摘要： Low-dimensional metal halides at molecular level, which feature strong quantum confinement effects from intrinsic structure, are emerging as ideal candidates in optoelectronic fields. However, developing stable and nontoxic metal halides still remains a great challenge. Herein, for the first time, high-crystalline and highly stable CsCu2I3 single crystal, which is acquired by a low-cost antisolvent vapor assisted method, is successfully developed to construct high-speed (trise/tdecay = 0.19 ms/14.7 ms) and UV-to-visible broadband (300–700 nm) photodetector, outperforming most reported photodetectors based on individual all-inorganic lead-free metal halides. Intriguingly, facet-dependent photoresponse is observed for CsCu2I3 single crystal, whose morphology consists of {010}, {110}, and {021} crystal planes. The on–off ratio of {010} crystal plane is higher than that of {110} crystal plane, mainly owing to lower dark current. Furthermore, photogenerated electrons are localized in twofold chains created by [CuI4] tetrahedra, leading to relatively small effective mass and fast transport mobility along the 1D transport pathway. Anisotropic carrier transport characteristic is related to stronger confinement and higher electron density for {110} crystal planes. This work not only demonstrates the great potential of CsCu2I3 single crystal in high-performance optoelectronics, but also gives insights into 1D electronic structure associated with fast photoresponse and high anisotropy.
关键词： photodetectors,facet-dependent photoresponse,1D electronic structures,highly stable,fast response
更新于2025-09-23 15:21:01
-
Simulation and experimental study of the angle-dependent sensitivity of the thick pinhole used for gamma imaging
摘要： The angle-dependent sensitivity of rotationally symmetric thick pinholes used for gamma imaging was investigated using a geometric algorithm and Monte Carlo numerical simulations for the thick pinholes with different structural parameters. The effect of the pinhole diameter, the thickness of the straight-hole portion, and the half conical angle were analyzed. The point source was demonstrated to be a feasible replacement for the homogeneous plane source through theoretical deduction, numerical calculations, and experimental measurements of the angle-dependent sensitivity. A small quasi-point source was established based on a 10K curie level 60Co gamma ray source in the experimental measurement of the angle-dependent sensitivity. The image position remained unchanged and image distortion was avoided by rotating the thick pinhole around the pinhole center. The experimental result was in good agreement with the theoretical calculation, indicating the potential of this measurement method.
关键词： angle-dependent sensitivity,Monte Carlo method,quasi-point source,geometrical numerical algorithm,thick pinhole imaging
更新于2025-09-23 15:21:01
-
Pathways to excitation of atoms with bicircular laser pulses
摘要： We study the excitation of the hydrogen atom by bichromatic circularly polarized laser pulses using numerical solutions of the time-dependent Schr?dinger equation. The results are in agreement with the selection rules for multiphoton processes in such fields, namely, excited states are populated in which orbital angular momentum and magnetic quantum numbers are either both odd or both even, independent of the relative helicity, peak intensity, and pulse duration of the pulses. For co-rotating pulses the results show that excitation predominantly proceeds to states with magnetic quantum number of the same helicity as the laser pulses. Besides pathways via direct photon absorption from the ground state our results indicate that a transfer of population among the Rydberg states occurs via (cid:2)-type transitions. In the case of counter-rotating pulses the largest excitation probability is found for Rydberg states that differ in magnetic quantum number by (cid:3)m = ±3. This pattern allows us to estimate how many photons from each of the two bichromatic fields have been absorbed. Finally, we confirm that a population in Rydberg states beyond a maximum orbital angular quantum number is unlikely.
关键词： Rydberg states,hydrogen atom,bichromatic circularly polarized laser pulses,time-dependent Schr?dinger equation,multiphoton processes
更新于2025-09-23 15:21:01
-
A general approach for the calculation and characterization of x-ray absorption spectra
摘要： We present a general approach for the calculation and assignment of X-ray absorption spectra based on electronic wavepacket propagations performed using explicitly time-dependent electronic structure calculations. Such calculations have the appeal of yielding the entire absorption spectrum for the cost of a single set of electronic wavepacket propagations, obviating the need to explicitly calculate large numbers of core-excited states. The spectrum can either be calculated from the Fourier transform of the time-dependent dipole moment or from the Fourier transform of the wavepacket autocorrelation function. We propose that calculating the absorption spectrum using the latter approach will generally be the preferred option. This method has two important advantages. First, the autocorrelation functions can be obtained for twice the propagation time, resulting in a halving of the computational effort required to calculate the spectrum relative to the time-dependent dipole moment approach. Second, using the tools of filter diagonalisation, the autocorrelation functions may be used to determine the time-independent final core-excited states underlying the peaks of interest in the spectrum. The proposed scheme is validated by calculating and characterizing the X-ray absorption spectra of benzene and trifluoroacetonitrile at the time-dependent second-order algebraic diagrammatic construction level of theory.
关键词： time-dependent electronic structure calculations,X-ray absorption spectra,core-excited states,electronic wavepacket propagations,filter diagonalisation
更新于2025-09-23 15:21:01
-
Temperature dependent Raman frequency model for monoatomic crystals
摘要： In the present study, a theoretical model for the temperature dependence of Raman frequency shift without any adjustable parameters is established. The model builds a relationship between the temperature dependent Raman frequency and the Raman frequency at a reference temperature. To verify the present model, the temperature dependent Raman frequency shifts of Ge, α-Sn, and Si are predicted, which are in excellent agreement with the available experimental results, Balkanski’s theory and Kolesov’s theory. Besides, the model indicates that the variations in special heat with temperature determine the temperature dependent Raman frequency. This work can provide a convenient method to predict the temperature dependent Raman frequency shift for monoatomic crystals.
关键词： Raman frequency shift,semiconductor,temperature dependent,modelling
更新于2025-09-23 15:21:01