4f结构脉冲整形器失调对光场空间分布的影响

利用零色散脉冲整形装置的模型，从理论上详细讨论了4f结构脉冲整形装置中第一光栅和第一凸透镜之间距离失调、两凸透镜之间距离失调以及第二凸透镜与第二光栅之间距离失调对输出脉冲空间特性的影响。     

4f结构间距失调对达曼类滤波器输出脉冲特性的影响

 研究了4f结构的飞秒脉冲时空变换整形装置在各元件间距不等的情况下对脉冲输出特性的影响，理论分析了间距失调效应对等间距和不等间距达曼光栅滤波器的脉冲输出特性的影响。结果表明4f结构间距失调后无论是能量还是平均度都不如等间距高，中心脉冲能量变小，其它级次脉冲生出更多旁瓣；失调量越小，输出的脉冲质量越高，对于f为12 cm的装置，当失调量小于1 cm时，对输出脉冲影响较小。     

Variation of the speckle contrast in a graded-index fibre by misalignment of the incident beam

The speckle pattern observed at the output end of a multimode fibre is closely related to the modal noise. In this paper, the average contrast of the speckle pattern is studied as a function of the radial position in the output end plane for three kinds of misalignment of the incident beam, i.e. defocusing, axial misalignment and angular misalignment. It is found that a variation of the speckle contrast is very sensitive to all kinds of misalignment of the incident beam and that its varying form strongly depends on the kind of misalignment of the incident beam. The speckle contrast at the centre of the output end plane is also examined as a function of the magnitude of misalignment. It is found that the contrast increases from a minimum value in the correct alignment to a certain saturated value with an increase of misalignment.     

超高亮度激光系统中光栅对脉冲整形器失调对输出脉冲时间特性的影响

在较全面地给出光栅对脉冲整形器失调产生附加相位项表达式的同时，详细地讨论了展宽器失调的附加相位放大系统传输过程中的变化，并与压缩器失调特性作了比较，分析了这些失调对超高亮度激光系统输出脉冲及其聚焦场时间特性的影响，得到了确定光栅对脉冲整形器失调容限的基本原则。     

Angular chirp and tilted light pulses in CPA lasers

We investigate analytically and experimentally various aspects of the angular chirp of ultrashort laser pulses. This type of chirp is easily produced by slight misalignment of standard pulse stretcher and/or compressor setups. Angular chirp leads to tilted pulse fronts in the near field and to a strong reduction of intensity in the focus. The effect is rather difficult to observe with standard diagnostic techniques. We present a method that is based on interferometric field autocorrelation and allows us to measure the angular chirp reliably. Suggestions on how to avoid this effect are outlined as well.     

Wide spectral range third-order autocorrelator based on ultrafast nonresonant nonlinear refraction

We demonstrate a simple scheme for a wide spectral range, third-order autocorrelator based on ultrafast nonlinear Kerr-type refraction. The technique was successfully used to characterize high-energy ultrashort pulses at 1550 and 1300 nm, where the pulse's shape and width are two of the most critical parameters. Because of its simplicity, this technique is also a powerful tool for the optimization of high-power chirped-pulse amplified laser systems, in which slight misalignment of the stretcher-compressor gratings can lead to spatiotemporal pulse distortions. In addition, it can be extended to low-power mode-locked oscillators.     

Misalignment Fault Prediction of Wind Turbines Based on Improved Artificial Fish Swarm Algorithm

A misalignment fault is a kind of potential fault in double-fed wind turbines. The reasonable and effective fault prediction models are used to predict its development trend before serious faults occur, which can take measures to repair in advance and reduce human and material losses. In this paper, the Least Squares Support Vector Machine optimized by the Improved Artificial Fish Swarm Algorithm is used to predict the misalignment index of the experiment platform. The mixed features of time domain, frequency domain, and time-frequency domain indexes of vibration or stator current signals are the inputs of the Least Squares Support Vector Machine. The kurtosis of the same signals is the output of the model, and the 3σ principle of the normal distribution is adopted to set the warning line of misalignment fault. Compared with other optimization algorithms, the experimental results show that the proposed prediction model can predict the development trend of the misalignment index with the least prediction error.     

具有空间重叠性和时间同步性的双波长TEA CO2激光器研究

提出了一种改进的双波长TEA CO2激光器,不仅具有良好的空间重叠性,而且具有比较理想的时间同步性.该激光器由两个空间上部分重叠的光栅和一个锗镜构成光栅-平面腔,两个光栅前后放置,相互利用,共同建立双频振荡,由锗镜输出双波长激光.通过改变两光栅的有效面积,对两输出脉冲空间重叠性进行调节;通过改变两光栅的角度形成的失谐缩小输出脉冲的时间间隔,达到时间同步性.实验表明,可以在空间重叠性的基础上使两输出脉冲的时间间隔由1 000 ns调整到200 ns.     

Parameterized reduced order modeling of misaligned stacked disks rotor assemblies

Light and flexible rotating parts of modern turbine engines operating at supercritical speeds necessitate application of more accurate but rather computationally expensive 3D FE modeling techniques. Stacked disks misalignment due to manufacturing variability in the geometry of individual components constitutes a particularly important aspect to be included in the analysis because of its impact on system dynamics. A new parametric model order reduction algorithm is presented to achieve this goal at affordable computational costs. It is shown that the disks misalignment leads to significant changes in nominal system properties that manifest themselves as additional blocks coupling neighboring spatial harmonics in Fourier space. Consequently, the misalignment effects can no longer be accurately modeled as equivalent forces applied to a nominal unperturbed system. The fact that the mode shapes become heavily distorted by extra harmonic content renders the nominal modal projection-based methods inaccurate and thus numerically ineffective in the context of repeated analysis of multiple misalignment realizations. The significant numerical bottleneck is removed by employing an orthogonal projection onto the subspace spanned by first few Fourier harmonic basis vectors. The projected highly sparse systems are shown to accurately approximate the specific misalignment effects, to be inexpensive to solve using direct sparse methods and easy to parameterize with a small set of measurable eccentricity and tilt angle parameters. Selected numerical examples on an industrial scale model are presented to illustrate the accuracy and efficiency of the algorithm implementation.     

超短光脉冲波形研究

本文讨论了光脉冲技术发展中的脉冲波形测量问题。介绍了一种通用的光脉冲波形测量新方法,该方法可以给出光脉冲的波形、脉宽以及光脉冲内含的频率啁啾信息。这种测量方法已应用于半导体激光器产生ps光脉冲的实验研究,其可行性得到了验证。     

Experimental analysis of phase conjugation properties of four-wave mixing in an SOA after probe broadening due to fibre dispersion

Experimental results are presented which analyze the phase conjugation properties of four-wave mixing signals generated due to the beating between probe pulses broadened by a length of fibre and narrow pump pulses. This results in four-wave mixing pulses significantly narrower than the injected probe pulses albeit with reduced phase conjugation properties, which are examined. The pulses are completely characterized using the second-harmonic generation frequency resolved optical gating technique. The probe pulse is initially broadened due to propagation through 40 m of dispersion compensating fibre. This causes the probe pulse to be much wider than the injected pump pulse, in contrast to previously reported results. The four-wave mixing signal is therefore both wavelength converted and compressed, due to the gating properties of four-wave mixing, with respect to the initial probe signal. The phase conjugation properties of the converted signal are discussed and this signal is then passed through a second length of dispersion compensating fibre in order to further compress the pulse and to examine in more detail the phase conjugation properties.     

甲酸根离子掺杂的AgCl乳剂增感后的光电子特性研究

甲酸根离子作为一种“空穴－电子转换剂”掺杂在卤化银中可以提高潜影形成过程中光电子的利用率。将不同位置甲酸根离子掺杂的立方体AgCl乳剂又经相同条件的硫加金或感绿染料增感后，采用微波吸收介电谱检测技术对样品在脉冲激光作用下所产生的光电子衰减信号进行检测，通过分析光电子的衰减特性，发现甲酸根离子仍然能发挥其空穴陷阱效应，而且自由光电子的衰减时间和寿命与未增感的掺杂乳剂随掺杂位置的变化趋势一致。     

光栅面不平行对压缩脉冲时空特性的影响

 推导了光栅对压缩器两光栅在垂直于刻线的平面(衍射面)内有一夹角时1至4阶色散变化量的表达式,以及脉冲超高斯光束经光栅对压缩后的场分布。并据此模拟分析了光栅表面平行性失调对输出脉冲时空特性的影响。结果表明：脉冲光束单次通过光栅对时其波形会产生扭曲,光栅对的失调会使脉冲扭曲更加严重;而两次通过光栅对时横向谱移动的影响会消除,但脉冲将出现旁瓣,光栅对的失调使得脉冲在时间上提前,且色散阶数越高色散变化量对压缩脉冲时空特性的影响越大。     

非线性自加速光场及其应用

近年来，艾里光束/脉冲等光场因其独特的自加速传输特性以及在诸多应用中表现出的优势引起了人们极大的研究兴趣。但在非线性环境中，这类光场却面临失去其特殊结构以及加速特性的困境。为了解决这一问题，非线性自加速光场应运而生，使得非线性过程具有加速的特质。本文基于作者近期的工作回顾了非线性自加速光场的研究进展。首先讨论了它们的物理图像以及它们与艾里光场的联系，其次详细介绍了自加速特性在非线性调控、非线性响应函数的可视化以及光控光中的独特应用优势，最后介绍了一种新式的光场自加速行为|| 可类比于经典力学中正负质量物质的相互作用过程。这些非线性自加速光场可让非线性动力学过程在弯曲时/空发生，能引起平坦空间无法实现的新现象与新应用。     

Dissipation and dispersion properties of microinhomogeneous media

The propagation of a harmonic elastic wave in a microinhomogeneous (defect-containing) medium is considered in the framework of the rheological model that reperesents the medium in the form of a one-dimensional chain of masses connected by purely elastic elements and by Kelvin-Voigt viscoelastic elements. Analytical expressions are derived for the dissipation and dispersion characteristics of this medium for various distributions of the parameters of the viscoelastic elements. The dissipation and dispersion properties are found to obey the Kramers-Kronig relations. It is also shown that the damping decrement of the wave is almost constant, and the phase velocity monotonically increases in a sufficiently wide range of parameters of the viscoelastic elements in a wide frequency band. The derived expressions for the dispersion and dissipation are used to simulate the propagation of broadband pulses in this kind of medium.     

Role of the longitudinal piston error in a tiled-grating compressor in second and high-order harmonic generation

In this work, we study the limitations for overcoming the longitudinal piston error in a femtosecond tiled-grating compressor using nonlinear measurements like second harmonic generation. In particular, we observe the influence of this error when developing high-power laser experiments such as high-order harmonic generation. The generation of nonlinear processes with femtosecond pulses compressed in tiled-grating systems is studied. Special attention is paid to the role of the longitudinal piston error which is the most difficult to overcome in the compressor alignment. A complex spatio-temporal structure is expected to appear due to that misalignment. Both second harmonic generation in nonlinear crystals and high-order harmonic generation in gases are studied and a strong dependence with piston error is found, thus leading to a sub-micron modulation in the generated signal. In particular, the high sensitivity of the high-order harmonics to the longitudinal position allows one to use this processes for the accurate alignment of the compressor to few tens of nanometers.     

衰荡腔测量中的腔参数选择

 基于谐振腔失调灵敏度参量随腔长的变化关系,提出了一种衰荡腔,它是由共焦腔将腔长缩短为原来的0.73得到的稳定腔。根据光束传输规律和失调腔矩阵方法,以及光腔衰荡法测量原理和曲线拟合方法,建立了腔长、腔镜角度失调下光腔衰荡法的反射率测量模型。通过数值模拟,研究了这种稳定衰荡腔中,腔微小失调对反射率测量结果的影响,并与相同失调情况下共焦衰荡腔的测量结果进行了对比分析。结果表明,这种稳定腔用作衰荡腔,测量结果受腔镜角度失调影响较大,而受腔长失调影响小;其长度较短,便于工程应用;衍射损耗较小,测量精度高。     

Pulse‐shape instabilities and their measurement

Multi‐shot pulse‐shape measurements of trains of ultrashort pulses with unstable pulse shapes are studied. Measurement techniques considered include spectral‐phase interferometry for direct electric‐field reconstruction (SPIDER), second harmonic generation frequency‐resolved optical gating (FROG), polarization gate FROG, and cross‐correlation FROG. An analytical calculation and simulations show that SPIDER cannot see unstable pulse‐shape components and only measures the coherent artifact. Further, the presence of this instability cannot be distinguished from benign misalignment effects in SPIDER. FROG methods yield a better, although necessarily rough, estimate of the pulse shape and also indicate instability by exhibiting disagreement between measured and retrieved traces. Only good agreement between measured and retrieved FROG traces or 100% SPIDER fringe visibility guarantees a stable pulse train.     

光子器件激光封装中热致角度偏移的降低

对光电子器件激光封装中光纤准直器的热致角度偏移进行了实验研究和理论分析.设计了一种新型的拱形焊接支承架,并对其热稳定性进行了测试.测试结果表明,在加载十个连续的温度循环周期后,其角度偏移为0.01°,而在同样的测试条件下,传统的鞍形支承架的角度偏移达到0.023°.采用非线性热—应力耦合有限元模型对封装结构中热应力的变化、残余应力的分布以及准直器角度偏移进行分析.理论分析结果与实验结果极好地吻合.进一步的理论计算得到新型拱形支承架的饱和热致角度偏移为0.043°,与传统鞍形支承架的0.065°相比得到了较大的降低.     

小型短电磁脉冲传感器

对一种短偶极子类小型短电磁脉冲传感器进行了研究,分析了传感器电容、有效面积与结构参数之间的解析关系,给出了传感器的工作原理。根据应用需求设计了不同带宽的该类传感器,并对其波形保真性和有效面积进行了数值分析,仿真结果表明:经传感器接收并还原所得场波形与激励电场波形几乎完全重合,传感器有效面积与理论分析结果偏差小于1%。对传感器的焊接、定位和对轴等制作工艺进行了研究,完成了传感器样品的制作。利用单锥TEM室对传感器的波形保真性和有效面积进行了实验测试,测试结果表明:设计制作的传感器样品可以很好地恢复待测脉冲电场的波形和幅度,两支传感器样品的有效面积实测结果与解析计算结果较为一致,偏差分别小于4%和7%。