Compensation for self-focusing by use of cascade quadratic nonlinearity

We demonstrate theoretically and experimentally compensation for positive Kerr phase shifts with negative phases generated by cascade quadratic processes. Experiments show correction of small-scale self-focusing and whole-beam self-focusing in the spatial domain and self-phase modulation in the temporal domain. (C) 2001 Optical Society of America.

Quadratic nonlinear technologies for femtosecond lasers

Quadratic optical nonlinearity chi((2)) can be exploited in femtosecond lasers and regarded as a significant new degree of freedom for the design of short-pulse sources. We will review our recent progress on developing nonlinear quadratic technologies for femtosecond lasers. Our nonlinear laser technology offers new properties for femtosecond lasers, including optical parametric amplifier with novel working regime, efficient second harmonic generation, and time telescope.

on quadratic bent functions in polynomial forms

In this correspondence, we construct some new quadratic bent functions in polynomial forms by using the theory of quadratic forms over finite fields. The results improve some previous work. Moreover, we solve a problem left by Yu and Gong in 2006.

A QUASI-SIMPLEX METHOD FOR STRICTLY CONVEX QUADRATIC PROGRAMMING

本文提出一个不用 Kuhn- Tucker条件而直接搜索严格凸二次规划最优目标点的鲁棒方法 .在搜索过程中 ,目标点沿约束多面体边界上的一条折线移动 .这种移动目标点的思想可以被认为是线性规划单纯形法的自然推广 ,在单纯形法中 ,目标点从一个顶点移到另一个顶点。

Identification of Nonlinear Systems Through Time-Frequency Filtering Technique

In the previous paper, a class of nonlinear system is mapped to a so-called skeleton linear model (SLM) based on the joint time-frequency analysis method. Behavior of the nonlinear system may be indicated quantitatively by the variance of the coefficients of SLM versus its response. Using this model we propose an identification method for nonlinear systems based on nonstationary vibration data in this paper. The key technique in the identification procedure is a time-frequency filtering method by which solution of the SLM is extracted from the response data of the corresponding nonlinear system. Two time-frequency filtering methods are discussed here. One is based on the quadratic time-frequency distribution and its inverse transform, the other is based on the quadratic time-frequency distribution and the wavelet transform. Both numerical examples and an experimental application are given to illustrate the validity of the technique.

Dynamic stress intensity factor of a functionally graded material under antiplane shear loading

The dynamic response of a finite crack in an unbounded Functionally Graded Material (FGM) subjected to an antiplane shear loading is studied in this paper. The variation of the shear modulus of the functionally graded material is modeled by a quadratic increase along the direction perpendicular to the crack surface. The dynamic stress intensity factor is extracted from the asymptotic expansion of the stresses around the crack tip in the Laplace transform plane and obtained in the time domain by a numerical Laplace inversion technique. The influence of graded material property on the dynamic intensity factor is investigated. It is observed that the magnitude of dynamic stress intensity factor for a finite crack in such a functionally graded material is less than in the homogeneous material with a property identical to that of the FGM crack plane.

Flows with Inertia in a Three-Dimensional Random Fiber Network

A fiber web is modeled as a three-dimensional random cylindrical fiber network. Nonlinear behavior of fluid flowing through the fiber network is numerically simulated by using the lattice Boltzmann (LB) method. A nonlinear relationship between the friction factor and the modified Reynolds number is clearly observed and analyzed by using the Fochheimer equation, which includes the quadratic term of velocity. We obtain a transition from linear to nonlinear region when the Reynolds numbers are sufficiently high, reflecting the inertial effect of the flows. The simulated permeability of such fiber network has relatively good agreement with the experimental results and finite element simulations.

Variable power singular interface elements for a crack normal to the bimaterial interface

Zero thickness crack tip interface elements for a crack normal to the interface between two materials are presented. The elements are shown to have the desired r(lambda-1) (0 < lambda < 1) singularity in the stress field at the crack tip and are compatible with other singular elements. The stiffness matrices of the quadratic and cubic interface element are derived. Numerical examples are given to demonstrate the applicability of the proposed interface elements for a crack perpendicular to the bimaterial interface.

The design of a controllable imaging device with the cold atomic medium

Under the circumstance of a Gaussian control field, the cold atomic medium with electromagnetically induced transparency (EIT) turns out to be the special medium with the quadratic index distribution which is controllable online. In our study, the optical system occupies a portion of the EIT medium which acts as an imaging device. With the help of the Collins formula, the analytic expression for the spatial distribution of the probe field in the cold atomic medium is obtained as well as the location of the imaging. The methods for improving the visibility of the imaging are proposed in this paper. Moreover, we also show that the shapes of the images on the output are strongly influenced by the intensity of the control field, which provides a potential optical processing method.

二次光栅在波前测量中的应用

采用一种特殊的二次光栅用于激光波前测量, 它对非零级衍射光束具有不同的聚焦效应, 其光栅线为圆弧型而非直线。导出了在会聚光束情况下的两平面成像在单一像平面上的距离关系, 实验上实现了二次光栅用于会聚光束的波前测量, 测量得到会聚光束具有较大的散焦(-2.93λ)和球差(1.34λ), 与该透镜引起波前的离焦像差理论理想值(-2.695λ)基本符合。该技术可以实现波前的高空间分辨力和高精度实时测量, 大大减少光学元件数量, 降低装置成本。由于大功率激光束的不稳定性, 其波前变化非常快, 所以该方法的实时性非

合成孔径激光成像雷达(Ⅰ):离焦和相位偏置望远镜接收天线

把合成孔径激光成像雷达的目标衍射区分为三个区域,提出采用离焦或者附加空间相位调制板的光学接收望远镜补偿回波像差。当目标处于菲涅耳衍射区时可采用离焦或偏置望远镜补偿回波二次项离焦像差并产生用于孔径合成的二次项相位历程;目标处于夫琅和费衍射区时可以采用离焦或偏置望远镜补偿回波二次项离焦像差但不产生相位历程;目标处于瑞利-索末菲衍射区域时不可能补偿回波高阶像差。

合成孔径激光成像雷达(Ⅱ):空间相位偏置发射望远镜

报道一种可以进行空间相位偏置的光学望远镜,用作合成孔径激光成像雷达中的光学发射天线。在望远镜内放置相位调制平板,控制望远镜的离焦量和位相调制平板的相位函数,能够在激光望远镜的照明区产生可控制的附加空间相位二次项,灵活改变激光照明波前,以在目标回波接收信号中产生雷达运动方向上的所需的二次项相位历程,因此能够实现特定的方位向成像分辨率。

合成孔径激光成像雷达(Ⅲ):双向环路发射接收望远镜

提出了一种用于合成孔径激光成像雷达的双向环路结构的发射接收望远镜,双向环路包括发射4-f转像系统、接收4-f转像系统和独立的望远镜。发射通道中设置离焦和相位调制平板偏置,接收通道中设置离焦和相位平板偏置。控制发射离焦量,发射相位调制函数,接收离焦量,接收相位调制函数,用同一个望远镜可以同时实现空间二次项相位附加偏置的激光发射和消除目标点散射回波接收波面像差的离焦光学接收,并产生雷达运动方向上合适的和可控制的相位二次项历程,从而实现孔径合成成像。详细介绍了系统设计,给出了从发射到光电外差接收的全过程传输方程。

基于PLZT的电光偏转器的特性研究

采用具有高二次电光效应的掺镧锆钛酸铅陶瓷材料（PLZT），设计和制备了一种基于折射率随外加电压发生变化的电光偏转器。构建了测试系统，测得PLZT的电光系数是R33=2.1

Upconversion and fluorescence spectral studies of Er3+/Yb3+-codoped Bi(2)Q(3)-GeO2-Ga(2)Q(3)-Na2O glasses

The absorption spectra and upconversion fluorescence spectra of Er3+/-Yb3+-codoped natrium-gallium-germanium-bismuth glasses are measured and investigated. The intense green (533 and 549 nm) and red (672 nm) emission bands were simultaneously observed at room temperature. The quadratic dependence of the green and red emission on excitation power indicates that the two-photon absorption processes occur. The influence of Ga2C3 on upconversion intensity is investigated. The intensity of green emissions increases slowly with increasing Ga2O3 content, while the intensity of red emission increases significantly. The possible upconversion mechanisms for these glasses have also been discussed. The maximum phonon energy of the glasses determined based on the infrared (IR) spectral analysis is as low as 740 cm(-1). The studies indicate that Bi2O3-GeO2-Ga2O3-Na2O glasses may be potential materials for developing upconversion optical devices (c) 2006 Published by Elsevier B.V.