Photoreflectance study on the photovoltaic effect in InAs/GaAs quantum dot solar cell

To investigate the effect of quantum dot (QD) layers on the photovoltaic process of InAs/GaAs QD solar cell (QDSC), QD layers were embedded in conventional GaAs p-n junction SC (GaAs SC) structures. The photoreflectance (PR) was examined at different temperatures (T) and excitation light intensities (I_ex) to investigate the photovoltaic effects through observation of the Franz-Keldysh oscillations (FKOs) in the PR spectra. The evaluated the p-n junction electric fields (F_pn) of the InAs QDSC was different from that of the GaAs SC. Moreover, InAs QDSC show that the different photovoltaic behaviors compared with GaAs SC by varying I_ex and T. From these considerations, we suggest that the different photovoltaic behaviors are caused by the effect of the additional photo-carrier generation in InAs QD layers resulting in enhancement of the field screening effect in F_pn.     

Basic properties of nonlinear surface charge waves at a plasma boundary

The nonlinear properties of surface charges are here analyzed under ideal conditions. We thus deduce a new single equation from the wellknown equations which govern the cold electron plasma motion. Simple formulas that describe the propagation of surface charge perturbations along the plasma boundary are also found.     

Numerical Simulation of a Liquid Drop Freely Oscillating

Free oscillations of a viscous liquid drop surrounded by a dynamically inactive ambient gas, in zero gravity, are investigated numerically using FIDAP^TM package in the axisymmetrical case. The full Navier‐Stokes equations with appropriate interfacial conditions are solved by using Galerkin/Finite element technique along with the spine method for the advection of the free boundary are used. The aim of this preliminary study is to demonstrate the ability of the package to accurately solve nonlinear free surface problems. Oscillations of viscous drops released from an initial static deformation of small‐ to large‐amplitude proportional to the second spherical harmonic, without initial internal circulation, are considered. Accuracy is attested by demonstrating that (i) the drop volume remains constant, (ii) dynamic response to small and moderate amplitudes agrees well with linear and weakly non‐linear perturbation theories, (iii) large amplitude oscillations compare well with some numerical and experimental published results.     

Excitation of Forbidden Electronic Transitions in Atoms by Hermite–Gaussian Modes

Photoexcitation of trapped ions by Hermite–Gaussian (HG) modes from guided beam structures is proposed and investigated theoretically. In particular, simple analytical expressions for the matrix elements of induced atomic transitions are derived that depend both on the parameters of HG beams and on the geometry of an experiment. By using these general expressions, the ${}^2{S}_{1/2}\to {}^2{F}_{7/2}$ electric octupole (E3) transition is investigated in an Yb⁺ ion, localized in the low–intensity center of the HG₁₀ and HG₀₁ beams. It is shown how the corresponding Rabi frequency can be enhanced by properly choosing the polarization of incident light and the orientation of an external magnetic field, which defines the quantization axis of a target ion. The calculations, performed for experimentally feasible beam parameters, indicate that the achieved Rabi frequencies can be comparable or even higher than those observed for the conventional Laguerre–Gaussian (LG) modes. Since HG-like modes can be relatively straightforwardly generated with high purity and stability from integrated photonics, these results suggest that they may form a novel tool for investigating highly-forbidden atomic transitions.