Examining surface and bulk structures using combined nonlinear vibrational spectroscopies

We combined sum-frequency generation (SFG) vibrational spectroscopy with coherent anti-Stokes Raman scattering (CARS) spectroscopy in one system to examine both surface and bulk structures of materials with the same geometry and without the need to move the sample. Poly(methyl methacrylate) (PMMA) and polystyrene (PS) thin films were tested before and after plasma treatment. The sensitivities of SFG and CARS were tested by varying polymer film thickness and using a lipid monolayer.     

Manipulating supercontinuum generation by minute continuous wave

We report a simple triggering mechanism that greatly enhances and stabilizes supercontinuum generation by using an extremely weak cw light (~200,000 times weaker than the pump light). Such an active manipulation scheme can be enabled by a wide range of input conditions and circumvents complex techniques such as precise time delay tuning and dedicated feedback control. It thus offers a handy and versatile approach to control and optimize supercontinuum generation, expanding its range of applications, including ultrafast all-optical signal processing, spectroscopy, and imaging. The utility of the present technique for improving signal integrity in chirped pump optical parametric amplification is also demonstrated.     

Method for suppressing the mirror image in Fourier-domain optical coherence tomography

A method, novel to our knowledge, for effective mirror image suppression in Fourier-domain optical coherence tomography based on a phase shift between neighboring A-mode scans is demonstrated. By realizing that the phase shifts of the real and mirror images are mutually reversed and assuming that the real image intensities of the two successive A-mode scans are the same, we can solve a set of two coupled equations to obtain the real image signals. The images based on the scanning of a high-resolution spectral-domain optical coherence tomography system are processed to show effective mirror image suppression results. Compared with a similar method of broad application, our approach has the advantages of shorter process time and higher flexibility in selecting the concerned image portions for processing.     

Tuning of optical resonances in asymmetric microtube cavities

We tune optical resonances in rolled-up SiO/SiO(2) microtube cavities by gradually modifying the tube structure through asymmetrical postdeposition of SiO(2). Spectral blueshifts followed by redshifts of the resonant modes are observed in a thin-walled microtube (tube-I), which is attributed to a competition between shape deformation and effective increase of tube wall thickness. In contrast, only a monotonic redshift is detected when asymmetrical deposition is performed on a thick-walled microtube (tube-II). Distinct wavelength-dependent tuning was revealed in both kinds of tubes. Numerical calculations based on perturbation theory are carried out to explain and confirm the experimental results.     

可调光瞳滤波器的轴向焦移及扩展焦深

光学超分辨、焦深扩展及焦移3种效应一直受到研究人员的关注,且在光学显微成像、光学校准、光学相干层析成像及光存储中有着重要的应用.提出一种可调谐光瞳滤波器来实现光学系统的轴向焦移及扩展焦深.该光瞳滤波器由两个完全相同且相互平行的λ/4波片和置于其间的λ/2波片组成,其中λ/2波片分为两个可作相对旋转的区域,并且通过推导得...     

大气湍流随机相位差的相关解调算法研究

根据大气光学湍流的光纤干涉测量技术原理及其信号表现形式,针对湍流相位变化的随机性和复杂性,提出了能够实时解调湍流随机相位差的相关解调算法,数值模拟了固定相位差、波形相位差以及符合湍流频谱特征的随机相位差的解调.结果表明,此算法的绝对误差小于10-3,满足湍流测量的要求.该研究为实现光学湍流相位差的动态检测提供了必要的理...     

Design and end chamfer simulation of PEFP beam line curved dipole magnets

The design, fabrication and field measurement of 11 DC curved dipole magnets for the PEFP Beam Line have been completed. In this paper, a design method for a complex end chamfer using OPERA-3D is proposed. The conventional method for estimating chamfer shape is extended and applied to a curved dipole magnet by a coordinate transformation. Using the interface with CAD software, the complex end chamfer is modeled and fully determined by 3D simulation to meet the field uniformity requirement. The magnetic field measurement results are in good agreement with the simulation. The design considerations, field simulation results, end chamfer development process and measurement results are presented in detail.     

The fractional variational iteration method using He's polynomials

In this Letter, by introducing He's polynomials in the correct functional, we propose a new fractional variational iteration method to solve nonlinear time-fractional partial differential equations involving Jumarie's modified Riemann-Liouville derivative. Several examples have been solved to illustrate the proposed method is quite effective and convenient for solving kinds of nonlinear fractional order problems.     

Possible origin of ferromagnetism in un-doped ZnO: First-principles calculations

We performed first-principles calculations to investigate the electronic structures and magnetic properties of neutral and charged intrinsic defects of wurtzite ZnO. Our results show that an isolated single charged Zn vacancy can introduce a magnetic moment of 1.00μB, and may be responsible for the unexpected ferromagnetism in the system.