PPLN晶体差频测量飞秒激光脉冲的载波包络相移

在飞秒激光频率梳系统中，通常采用自参考技术测量飞秒激光脉冲的载波包络相移，但该技术需要采用光子晶体光纤进行光谱扩展从而增加了系统的不稳定性，这种技术已经制约了高稳定度的飞秒激光频率梳的发展.采用PPLN晶体差频法测量了宽谱钛宝石振荡器输出的7fs激光脉冲的载波包络频移，得到了大于30dB的拍频信号，为研制无光纤的新一代高稳定度光学频率梳奠定了基础.     

高功率激光系统随机相位屏的特性研究

 高功率激光系统中随机相位屏的统计模型出发,分析了其相位噪声及梯度的一阶和二阶统计性质。研究了完全相干光与部分相干光通过随机相位屏后的传输性质,推导得出部分相干光在经过随机相位屏后,其交叉谱密度的期望等于随机相位屏透过率函数的期望与入射光交叉谱密度的乘积。对该模型下的远场分布进行了数值模拟。结果显示,能量对称分布的完全相干光通过相位干屏后,只有通过随机相位屏透过率函数期望的远场分布是对称的;部分相干光在传输通过随机相位屏后,其谢尔模光束性质不会改变,但光强分布不再具有对称性,且强度明显降低。     

同时实现介电常数和磁导率为负的H型结构单元左手材料

基于用一种结构同时实现材料介电常数和磁导率为负的思想，提出了H型结构单元左手材料模型.采用矩形波导法测试表明，H型结构单元在微波频率范围出现左手透射峰，并且可以由参数t对左手特性区域进行调控.同时利用相位法、棱镜折射法和散射参量法从实验和理论证明了在左手透射峰区域材料的折射率为负值，介电常数和磁导率亦同时为负.相对由金属开口谐振环与金属线两种结构组合实现的左手材料，H型结构集磁谐振与电谐振于一体，结构简单、制备方便，对微波器件左手材料表现出更多的优越性.     

傅里叶变换轮廓术中新的相位及高度算法分析

在传统傅里叶变换轮廓术三维面型测量中,为了准确得到被测物体的高度分布,必需保证投影仪出射光瞳和摄像机入射光瞳的连线与参考面平行并且在同一水平面,否则存在较大的误差。着眼于更普通的情况,讨论双瞳连线与参考面成某一夹角时的高度计算,推导出了非平行时的参考面光场及物面变形条纹光场的表达式,并给出了高度映射公式。因而,传统的傅里叶变换轮廓术测量成为角度α=0时的特例。该方法使傅里叶变换轮廓术的测量条件得到了放宽;易于通过移动投影装置或成像装置获取全场条纹;并为在难以实现双瞳与参考面平行的特殊环境下的测量提供了可行的方法。计算机模拟及实验均证实了该方法的有效性。     

The S-FFT calculation of Collins formula and its application in digital holography

We study analytically and numerically the properties of one-dimensional chain of cold ions placed in a periodic potential of optical lattice and global harmonic potential of a trap. In close similarity with the Frenkel-Kontorova model, a transition from sliding to pinned phase takes place with the increase of the optical lattice potential for the density of ions incommensurate with the lattice period. We show that at zero temperature the quantum fluctuations lead to a quantum phase transition and melting of pinned instanton glass phase at large values of dimensional Planck constant. After melting the ion chain can slide in an optical lattice. The obtained results are also relevant for a Wigner crystal placed in a periodic potential.     

Accurate determination of the absolute phase and temporal-pulse phase of few-cycle laser pulses

A Fourier analysis method is used to accurately determine not only the absolute phase but also the temporal-pulse phase of an isolated few-cycle (chirped) laser pulse. This method is independent of the pulse shape and can fully characterize the light wave even though only a few samples per optical cycle are available. It paves the way for investigating the absolute phase-dependent extreme nonlinear optics, and the evolutions of the absolute phase and the temporal-pulse phase of few-cycle laser pulses.     

Dispersive white-light spectral interferometry including the effect of thin-film for distance measurement

A spectral-domain white-light interferometric technique is used for measuring distances in a Michelson interferometer with a mirror represented by a thin-film structure (TFS) on a substrate. A fibre-optic spectrometer is employed for recording spectral interferograms that include wide wavelength range effects of dispersion in a cube beam splitter and multiple reflection within the TFS. Knowing the effective thickness of the beam splitter, its dispersion and parameters of the TFS and substrate, the positions of the second interferometer mirror are determined precisely by a least-squares fitting of the theoretical spectral interferograms to the recorded ones. We apply the technique to the beam splitter made of BK7 optical glass and to a uniform SiO₂ thin film on a silicon wafer. We compare the results of the processing that include and do not include the effect of the TFS.     

Optical nonlinearity measurement of 4-（N-methyl,N-hydroxyethl）amino,4＇-nitroazobenzene using a transmittance technique with a phase object（T-PO） with top-hat beams at 600-nm wavelength

The transmittance technique with a phase object（T-PO）,for measuring optical nonlinear coefficients is proposed with a top-hat beam.The sensitivity of the T-PO with a top-hat beam is a factor of 4 greater than that with a Gaussian beam.The validity of this method is verified by measuring the nonlinearity of a well-characterized liquid,CS 2 at 532-nm wavelength.The ease of use of this method has been proved by measuring a new compound 4-（N-methyl,N-hydroxyethyl）amino,4＇-nitroazobenzene（ANAB） at 600-nm wavelength,indicating that this method can be extended to the measurement of optical nonlinearities in a wide-band spectrum.     

Critical behavior of the absorbing state transition in the contact process with relaxing immunization

We introduce a model for the Contact Process with relaxing immunization CPRI  . In this model, local memory is introduced by a time and space dependence of the contamination probability. The model has two parameters: a typical immunization time τ$\tau$ and a maximum contamination probability a$a$. The system presents an absorbing state phase transition whenever the contamination probability a$a$ is above a minimum threshold. For short immunization times, the system evolves to a statistically stationary active state. Above _τc(a)${\tau }_c\left(a\right)$, immunization predominates and the system evolves to the absorbing vacuum state. We employ a finite-size scaling analysis to show that the transition belongs to the standard directed percolation universality class. The critical immunization time diverges in the limit of a→1$a\to 1$. In this regime, the density of active sites decays exponentially as τ$\tau$ increases, but never reaches the vacuum state in the thermodynamic limit.     

Multi-Type Directed Scale-Free Percolation

In this paper,we study a long-range percolation model on the lattice Z d with multi-type vertices and directed edges.Each vertex x ∈ Z d is independently assigned a non-negative weight Wx and a type ψx,where(Wx) x∈Z d are i.i.d.random variables,and(ψx) x∈Z d are also i.i.d.Conditionally on weights and types,and given λ,α 0,the edges are independent and the probability that there is a directed edge from x to y is given by pxy = 1 exp(λφψ x ψ y WxWy /| x-y | α),where φij 's are entries from a type matrix Φ.We show that,when the tail of the distribution of Wx is regularly varying with exponent τ-1,the tails of the out/in-degree distributions are both regularly varying with exponent γ = α(τ-1) /d.We formulate conditions under which there exist critical values λ WCC c ∈(0,∞) and λ SCC c ∈(0,∞) such that an infinite weak component and an infinite strong component emerge,respectively,when λ exceeds them.A phase transition is established for the shortest path lengths of directed and undirected edges in the infinite component at the point γ = 2,where the out/in-degrees switch from having finite to infinite variances.The random graph model studied here features some structures of multi-type vertices and directed edges which appear naturally in many real-world networks,such as the SNS networks and computer communication networks.