Talbot effect under illumination of double femtosecond laser pulses

The Talbot effect under illumination of double femtosecond laser pulses has been reported. Spectrums of double femtosecond laser pulses with phase differences are quite different from that of one single femtosecond laser pulse. Therefore, the Talbot images of the double femtosecond laser pulses with phase differences are different from that of one single femtosecond laser pulse. Specifically, for the phase difference corresponding to π, the Talbot image shows the largest difference from that of one single pulse. Experimental results are in good agreement with the theoretical analysis. The behaviors of Talbot images under double femtosecond laser pulses illumination cannot be obtained under one femtosecond laser pulse, monochromatic or polychromatic light illumination. Therefore, it is a new interesting optical phenomenon for the Talbot effect which should have potential applications.     

Experimental study of the Talbot effect under femtosecond laser illumination

Experimental results of the Talbot effect of an amplitude grating under femtosecond laser illumination are reported. Compared with Talbot image under continuous wave (CW) illumination, Talbot images under femtosecond laser illumination are different due to the wide spectral bandwidth and the Talbot images are more distorted at longer Talbot distances. The spectrums and the pulsewidths of femtosecond laser pulses are measured with the frequency-resolved optical gating (FROG) apparatus. Experimental results are in good agreement with the theoretical analysis.     

Talbot effect of a high-density grating under femtosecond laser illumination

The Talbot effect of a high-density grating under femtosecond laser illumination is analyzed with rigorous electromagnetic theory which is based on the Fourier decomposition and the rigorous coupled-wave analysis (RCWA). Numerical simulations show that the contrast of the Talbot images steadily decreases as the transmitted femtosecond laser pulses propagate forward and with wider spectrum width of the femtosecond laser pulses. The Talbot images of high-density gratings have much higher sensitivity of the spectrum widths of the incident laser pulses than those of the traditional low-density gratings. In experiments, the spectrums and the pulse widths of the incident pulses are measured with a frequency-resolved optical grating (FROG) apparatus. The Talbot images are detected by using a Talbot scanning near-field optical microscopy (Talbot-SNOM) technique, which are in coincidence with the numerical simulations. This effect should be useful for developing new femtosecond laser techniques and devices.     

脉冲加载下锥角绝缘子的激光辐照沿面闪络性能北大核心CSCD

通过搭建脉冲加载下的激光辐照沿面闪络实验平台,考察了锥角绝缘子受激光辐照时的真空沿面闪络性能。结果表明:不论是紫外光(266nm)还是可见光(532nm)辐照在阴极三相点或者样品中间,+45°锥角绝缘子构型的性能都要优于-45°锥角绝缘子,并且紫外辐照阴极三相点对沿面闪络电压的影响较大,因此在大型脉冲功率装置中应该避免射线对绝缘堆阴极三相点处的辐照。     

啁啾超短脉冲光波照射下光栅Talbot效应的研究

应用傅里叶频谱分析法，给出了光栅在啁啾超短脉冲光波照射下菲涅耳衍射方程并分析了其Talbot效应. 数值计算表明，在Talbot距离处的衍射光强不仅与照射的超短脉冲光波的宽度有关，而且与脉冲光波的啁啾有关. 根据光栅在Talbot距离处衍射光强的变化，给出了一种检验超短脉冲光波是否含有啁啾的简单方法. 关键词： 光栅 菲涅耳衍射 Talbot效应 啁啾超短脉冲激光     

脉冲加载下锥角绝缘子的激光辐照沿面闪络性能

通过搭建脉冲加载下的激光辐照沿面闪络实验平台, 考察了锥角绝缘子受激光辐照时的真空沿面闪络性能。结果表明：不论是紫外光（266 nm）还是可见光（532 nm）辐照在阴极三相点或者样品中间, +45锥角绝缘子构型的性能都要优于－45锥角绝缘子, 并且紫外辐照阴极三相点对沿面闪络电压的影响较大, 因此在大型脉冲功率装置中应该避免射线对绝缘堆阴极三相点处的辐照。     

光束整形在激光照明中的应用

提出利用光束整形技术提高激光照明均匀性、调节照明远场光斑尺寸的方法,用Easylaser激光仿真软件分析光束截断比对照明均匀性的影响,分析大气湍流条件下光束整形对照明均匀性的影响,并比较调节光束质量与光束整形对照明均匀性的影响。结果表明:光束整形具有调节照明激光远场光斑尺度及均匀性的能力,相位调节因子越大,整形后远场光斑半径越大、均匀性越好;光束截断比越大照明均匀性越好;弱湍流条件下,光束整形比调节光束质量的照明激光远场光斑均匀性更好。     

光束整形在激光照明中的应用

提出利用光束整形技术提高激光照明均匀性、调节照明远场光斑尺寸的方法,用Easylaser激光仿真软件分析光束截断比对照明均匀性的影响,分析大气湍流条件下光束整形对照明均匀性的影响,并比较调节光束质量与光束整形对照明均匀性的影响。结果表明：光束整形具有调节照明激光远场光斑尺度及均匀性的能力,相位调节因子越大,整形后远场光斑半径越大、均匀性越好;光束截断比越大照明均匀性越好;弱湍流条件下,光束整形比调节光束质量的照明激光远场光斑均匀性更好。     

LD激光照明

本文研究半导体激光器作为主动红外夜视照明光源所遇到的问题，讨论使用光纤对半导体激光器进行光束整圆和光斑均匀化的过程，并对各种光纤进行比较，提出解决夜视激光照明引起的模式噪声的方法。     

Spatial Fourier-transform polarimetry using space-variant subwavelength metal-stripe polarizers

A novel method for rapid polarization measurement is suggested. The method is based on a periodic space-variant polarizer that can be realized by use of subwavelength metal-stripe gratings. The Stokes parameters of the incident beam are determined by Fourier analysis of the space-variant intensity transmitted through the grating, thus permitting real-time polarization measurement. We discuss the design and realization of such polarizers and demonstrate our technique with polarization measurements of CO(2)-laser radiation at a wavelength of 10.6mum.     

生物光声层析成像中不均匀和不稳定照明解决方法

在生物组织光声层析成像(Photoacoustic?Tomography,?PAT)算法中,为了简化问题,通常假设在均匀和稳定照明的理想情况下,重建组织的初始声压分布图、光吸收能量分布图和光学特性参数分布图.但在实际应用中,当光在生物组织中传播时,会出现光衰减和光通量分布不均匀的情况,导致重建精度下降.本文对非理想条件...     

Internal and near-surface fields for a chiral sphere under arbitrary laser beam illumination

A general scheme for the investigation of scattering by a chiral sphere under arbitrary monochromatic laser beam illumination is presented. The scattered and internal fields are expanded by using appropriate spherical vector wave functions, and their expansion coefficients are determined by the boundary conditions and the projection method. Targeting multiple incidence forms such as Gaussian beam, Hermite–Gaussian beam, doughnut mode beam and zero-order Bessel beam, the influence and propagation of near-surface intensity field for a chiral sphere are analyzed. These properties are very important for studying the properties of chiral media, and for manipulating the optical tweezers and super-resolution imaging of particles.     

Dispersion of collective modes at inhomogeneous metal surfaces

A simple model in which electrons are assumed to be specularly reflecting on a plane located a distance u above the boundary of a homogeneous metallic region is proposed for studying dynamical properties of metal surfaces. This model is believed to incorporate essential effects of the inhomogeneity of a pure jellium surface in a new way. It leads to a strong reduction of hydrodynamic dispersion effects for long wavelengths surface plasmons, in agreement with experiment and with various previous calculations. The model is also applied to surface phonons and exact numerical dispersion curves for both surface phonons and plasmons at arbitrary wavelengths are presented.     

Confocal scanning laser ophthalmoscopy improvement by use of Mueller-matrix polarimetry

A new technique for improving the signal-to-noise ratio and the contrast in images recorded with a confocal scanning laser system is presented. The method is based on the incorporation of a polarimeter into the setup. After the spatially resolved Mueller matrix of a sample was calculated, images for incident light with different states of polarization were reconstructed, and both the best and the worst images were computed. In both the microscope and the opthalmoscope modes, the best images are better than the originals. In contrast, the worst images are poorer. This technique may be useful in different fields such as confocal microscopy and retinal imaging.     

Holograms produced with double-heterojunction laser illumination

Off-axis holograms have been constructed with a double-heterojunction (Ga, Al) As-GaAs semiconductor laser, and image reconstruction has been accomplished using a semiconductor and a He-Ne laser. The reconstructed real images were quite clear, and the signal-to-noise ratio of those images was about 10. Experiments suggest that semiconductor lasers can successfully be applied to coherent optics.     

激光主动照明光学系统设计

为提高跟踪测量系统对暗弱目标的探测能力,设计一套自动化激光主动照明光学系统,对跟踪测量视场范围进行主动辅助照明。该系统在0.2~5 km距离处的照明直径均为10 m,计算出其在-20℃及+45℃的温度调焦量,照明仿真结果表明系统照明不均匀性15%。通过研究系统像差对照明均匀性的影响,以及对设计的调光组进行分析,得到调光组移动量与照明距离之间的理论关系,表明自动调节调光组位置即可实现不同照明距离处的均匀照明。设计和分析结果表明,该主动照明系统能够自动调节调光组位置,实现跟踪测量视场内的均匀照明,有利于跟踪测量系统对于暗弱目标的探测。     

Electron diffraction at stepped homogeneous and inhomogeneous surfaces

Defect analysis at surfaces with LEED or RHEED have so far been essentially restricted to steps or superstructure domains. Even if there are no superstructures, variations of the scattering factor influence the spot profile. With the now available high-resolution instruments more details of the spot profile may be observed. Therefore it will be discussed how a careful study of the spot profile at different energies may be used to analyze a surface with simultaneous steps and inhomogeneities. It will be shown how the asperity height is obtained without fitting parameters and how inhomogeneities are analyzed with respect to coverage and size distribution.     

The eigenmodes of a spatially inhomogeneous laser

The theory of the isothermal Hall-effect in intrinsic material is corrected taking into account arbitrary surface and bulk recombination and the departure from local electrical neutrality. The resulting formulas for the Hall voltage, the Hall field, the charge density, and the electron-hole current are valid for a weak magnetic field.     

Propagation of laser beams through inhomogeneous media

The propagation of gaussian beams in media with an arbitrary gain and/or dispersion profile is discussed using a variational method. Simple analytic formulae are derived and applied to the spin-flip laser which has a gaussian gain profile. The results are a significant improvement on the quadratic-gain approximation.