Laser Beam Shaping and Mode Conversion in Optical Fibers

塑造设备的所有纤维横梁的一个新班被蚀刻单个模式和 multimode 纤维的结束脸形成一个凹面锥尖端的逆认识到。凹面尖端纤维能与一致紧张分布把 Gaussian 横梁侧面变换成扁平的最高的横梁侧面。有约 5% 的紧张变化和到 67% 的点直径比率的扁平的最高的直径的一根扁平的最高的横梁被完成了。这台设备能也由移动观察飞机从 Gaussian 把横梁形状改变到一个甜甜圈。扁平的最高的 multimode 纤维横梁交货为要求高力量和一致紧张分发的应用是吸引人的。在单个模式纤维，凹面尖端能被用来减少横梁点尺寸直径，启用从单个模式纤维联合到综合光波导的有效的光。

Effect of the Reaction Field on Molecular Forces and Torques Revealed by an Image-Charge Solvation Model

We recently developed the Image-Charge Solvation Model(ICSM),which is an explicit/implicit hybrid model to accurately account for long-range electrostatic forces in molecular dynamics simulations[Lin et al.,J.Chem.Phys.,131,154103,2009].The ICSM has a productive spherical volume within the simulation cell for which key physical properties of bulk water are reproduced,such as density,radial distribution function,diffusion constants and dielectric properties.Although the reaction field(RF)is essential,it typically accounts for less than 2% of the total electrostatic force on a water molecule.This observation motivates investigating further the role of the RF within the ICSM.In this report we focus on distributions of forces and torques on water molecules as a function of distance from the origin and make extensive tests over a range of model parameters where Coulomb forces are decomposed into direct interactions from waters modeled explicitly and the RF.Molecular torques due to the RF typically account for 20% of the total torque,revealing why the RF plays an important role in the dielectric properties of simulated water.Moreover,it becomes clear that the buffer layer in the ICSM is essential to mitigate artifacts caused by the discontinuous change in dielectric constants at the explicit/implicit interface.

Hyperspectral Imaging Based on Compressive Sensing: Determining Cancer Margins in Human Pancreatic Tissue <i>ex Vivo</i>, a Pilot Study

Cancer is the second-leading cause of death in the United State and surgery remains the primary treatment for most solid mass tumors. However, accurately identifying tumor margins in real-time remains a challenge. In this study, the design and testing of hyperspectral imaging (HSI) system based on a single-pixel camera engine is discussed. The primary advantage of a single pixel architecture over traditional scanning HSI techniques is its high sensitivity and potential to function at low light levels. The objective for the imaging system described here is to detect changes in the reflectance spectra of tissue and to use these differences to delineate tumor margins. This paper presents the results of a 19-patient pilot study that assesses the ability of the HSI system to use reflectance imaging to delineate adenocarcinoma tumor margins in human pancreatic tissue imaged ex vivo. Pancreatic tissue excised during pancreatectomy was imaged immediately after being sent to the pathology lab. A pathologist sectioned the tissue and placed samples into standard tissue embedding cassettes. These tissue samples were then imaged using the HSI system. After imaging, the samples were returned to the pathologist for processing and analysis. The HSI was later compared to the histological analysis. The spectral angle mapping (SAM) and support vector machine (SVM) algorithms were used to classify pixels in the HSI images as healthy or unhealthy in order to delineate margins. Good agreement between margins determined via HSI (using both SAM and SVM) and histology/white light imaging was found.

Image Charge Methods for a Three-Dielectric-Layer Hybrid Solvation Model of Biomolecules

This paper introduces a three dielectric layer hybrid solvation model for treating electrostatic interactions of biomolecules in solvents using the PoissonBoltzmann equation.In this model,an interior spherical cavity will contain the solute and some explicit solvent molecules,and an intermediate buffer layer and an exterior layer contain the bulk solvent.A special dielectric permittivity profile is used to achieve a continuous dielectric transition from the interior cavity to the exterior layer.The selection of this special profile using a harmonic interpolation allows an analytical solution of the model by generalizing the classical Kirkwood series expansion.Discrete image charges are used to speed up calculations for the electrostatic potential within the interior and buffer layer regions.Semi-analytical and least squares methods are used to construct an accurate discrete image approximation for the reaction field due to solvent with or without salt effects.In particular,the image charges obtained by the least squares method provide accurate approximations to the reaction field independent of the ionic concentration of the solvent.Numerical results are presented to validate the accuracy and effectiveness of the image charge methods.

Introduction to non-Hermitian photonics in complex media:PT-symmetry and beyond

This special issue is dedicated to the emerging field of non-Hermitian photonics of complex media, with emphasis on PT-symmetric optical structures. In particular, the papers highlight the variety of applications being considered and the ways in which non-Hermitian optics can improve their performance.

Giant resonant light forces in microspherical photonics

Resonant light pressure effects can open new degrees of freedom in optical manipulation with microparticles,but they have been traditionally considered as relatively subtle effects.Using a simplified two-dimensional model of surface electromagnetic waves evanescently coupled to whispering gallery modes(WGMs)in transparent circular cavities,we show that under resonant conditions the peaks of the optical forces can approach theoretical limits imposed by the momentum conservation law on totally absorbing particles.Experimentally,we proved the existence of strong peaks of the optical forces by studying the optical propulsion of dielectric microspheres along tapered microfibers.We observed giant optical propelling velocities,0.45 mm s21 for some of the 15-20 mm polystyrene microspheres in water for guided powers limited at,43 mW.Such velocities exceed previous observations by more than an order of magnitude,thereby providing evidence for the strongly enhanced resonant optical forces.We analyzed the statistical properties of the velocity distribution function measured for slightly disordered(,1%size variations)ensembles of microspheres with mean diameters varying from 3 to 20 mm.These results demonstrate a principal possibility of optical sorting of microspheres with the positions of WGM resonances overlapped at the wavelength of the laser source.They can be used as building blocks of the lossless coupled resonator optical waveguides and various integrated optoelectronics devices.

Electron Raman scattering in a cylindrical quantum dot

Electron Raman scattering（ERS） is investigated in a CdS cylindrical quantum dot（QD）.The differential cross section is calculated as a function of the scattering frequency and the size of the QD.Single parabolic conduction and valence bands are assumed,and singularities in the spectrum are found and interpreted.The selection rules for the processes are also studied.The ERS studied here can be used to provide direct information about the electron band structure of these systems.