紧聚焦的超短超强激光脉冲在真空中加速斜入射的相对论电子

研究了紧聚焦的线偏振飞秒超强高斯激光脉冲俘获并剧烈加速斜入射低能相对论电子的效应，发现被俘获的电子在激光脉冲纵向有质动力的强大加速作用下，可以获得GeV量级的能量，并详细研究了入射电子的初能量、斜入射角、电子与激光脉冲的相对延迟时间和激光脉冲宽度等条件对电子能量增益的影响，发现当激光脉宽超过10λ时，脉宽对电子能量增益影响不大．

适用于中等耦合等离子体的碰撞算子

完全电离等离子体中，当试探粒子分布函数fα是关于试探粒子速度vα的偶函数时，导出了一个新的动力学方程的碰撞算子．该碰撞算子同时包括了大角散射（库仑近碰撞）和小角散射（库仑远碰撞）的二体碰撞的贡献，因此，该碰撞算子同时适用于弱耦合（库仑对数ln∧≥10）和中等耦合（库仑对数2≤ln∧≤10）等离子体．而且经过修改的碰撞算子和Rosenbluth势有直接的联系，当试探粒子和场粒子满足条件mα＜mβ（如电子-离子碰撞或Lorentz气体模型）和｜vα｜〉｜vβ｜时，经约化的电子-离子碰撞算子同最初的Fokker

压缩真空环境中无相互作用两量子比特系统的纠缠动力学

本文研究了压缩真空中无相互作用双原子的纠缠动力学特性。通过分析不同初始纠缠态的演化，发现压缩真空中纠缠原子失去纠缠的速度比在普通真空中更快，并且压缩越大纠缠衰减越快。可以用concurrence和可分性“距离”Lambda的时间演化来解释这种不同寻常的纠缠突然消失现象。

双暗态原子系统动力学行为的量子相干控制研究(英文)

量子相干控制前沿问题及应用研究是本世纪物理学前沿领域的重要研究内容.而基于暗态的量子相干控制技术已经导致了在相干布居捕获、绝热跟随、量子信息等多方面的应用.论文主要进行双暗态原子系统动力学行为的若干量子相干控制研究,包括双暗态四能级原子系统的绝热跟随特性研究,双暗态作用提高克尔非线性的新方案提出,自发辐射诱导相干实现非线性极化率的提高以及双通道高效四波混频过程的实现等.

Formation of nanogratings on the surface of a ZnSe crystal irradiated by femtosecond laser pulses

Two collinear femtosecond laser pulses, one at wavelength of 800 nm and the other at 400 nm (double frequency), simultaneously irradiated the surface of ZnSe crystal, which resulted in regular nanograting with period of 180 nm on the whole ablation area. We attribute the formation of the nanograting to be due to the interference between the surface scattered wave of 800 nm lasers and the 400 nm light. The period of the nanograting Lambda is about lambda/2n, where n is refractive index of the sample, and lambda, the laser wavelength. This mechanism is supported by observation of rotation of the nanograting with the polarization of 400 nm light, and by the dependence of Lambda similar to lambda of the nanoripples on the surface of semiconductors and dielectrics.

Ultraviolet-infrared femtosecond laser-induced damage in fused silica and CaF2 crystals

The damage in fused silica and CaF2 crystals induced by wavelength tunable femtosecond lasers is studied. The threshold fluence is observed to increase rapidly with laser wavelength lambda in the region of 250-800 nm, while it is nearly a constant for 800

Effects of relative phase in an open ladder system without incoherent pumping

We studied effects of the relative phase between the probe and driving fields on the absorption and dispersion properties in an open three-level ladder system with spontaneously generated coherence but without incoherent pumping. It is shown that by the phase controlling, switching from absorption to lasing without inversion (LWI) and enhancing remarkablely LWI gain can be realized; large index of refraction with zero absorption and the electromagnetically induced transparency can be obtained. We also find that varying the atomic injection and exit rates has a considerable influence on the phase dependent-absorption property of the probe field, existent of the atomic injection and exit rates gives the necessary condition of the realization of LWI, getting LWI is impossible in the corresponding closed system without incoherent pumping. We studied effects of the relative phase between the probe and driving fields on the absorption and dispersion properties in an open three-level ladder system with spontaneously generated coherence but without incoherent pumping. It is shown that by the phase controlling, switching from absorption to lasing without inversion (LWI) and enhancing remarkablely LWI gain can be realized; large index of refraction with zero absorption and the electromagnetically induced transparency can be obtained. We also find that varying the atomic injection and exit rates has a considerable influence on the phase dependent-absorption property of the probe field, existent of the atomic injection and exit rates gives the necessary condition of the realization of LWI, getting LWI is impossible in the corresponding closed system without incoherent pumping.

Phase control of cross-phase modulation with electromagnetically induced transparency

We investigate a four-level double-Lambda atomic scheme interacting with four laser fields, a weak probe field, a weak signal field and two driven fields, in a closed-loop configuration. We study the Kerr nonlinearity associated with cross-phase modulation based on electromagnetically induced transparency. Our results show, in this closed-loop system, that the strength of cross-phase modulation and two-photon absorption are dependent critically on the relative phase between the excitation paths. By choosing the parameters appropriately, large cross-phase modulation can be achieved within a wide transparency window, while two-photon absorption is cancelled completely. The strength of cross-phase modulation can be enhanced much more by decreasing the intensities of two driven fields.

石英波片偏光干涉谱的研究

根据石英晶体双折射率的色散特性,对石英波片的偏光干涉谱进行了理论分析和数值模拟,提出了一种石英波片延迟量和厚度的偏光干涉标定法。即由偏光干涉谱,可以得出石英波片在200～2000 nm宽光谱范围内的延迟量；通过对长波段的偏光干涉谱极值波长的精确判断,可以准确地计算出该石英波片的厚度。利用Lambda 900 紫外可见近红外分光光度计对一片石英波片的偏光干涉谱进行了测量。在波长精度为0.1 nm的情况下,测量的厚度精度为0.1 μm。误差分析结果表明,通过提高光谱的最小分辨力及选择较长的光谱波段进行测量计算

椭圆芯双模光纤干涉模斑中心间距的研究

通过弱波导近似的方法，讨论了椭圆芯双模光纤中沿光纤长轴的基模模斑半径Wx和短轴的基模模斑半径Wy尺寸，分析了它们的比值随入射光波长λ及纤芯半长轴与半短轴的比值a/b的变化规律。 针对基模LP01和第一高阶模LP11间的相位差变化，计算了双模干涉模斑的分布结构。计算结果表明，当基模LP01和第一高阶模LP11间的相位差为π/2时，两瓣干涉模斑有相同的结构特征。同时，两瓣模斑的中心间距S随Wx/Wy的的增加而变大。而且，当入射波长在0.65 μm和 1.31 μm之间变化时，结合两瓣模斑的中心间距S随Wx/Wy的变化规律，首次给出了S的计算公式。这对于实际应用如传感器和光纤耦合器件设计是很重要的。

Measurement of the diffraction-limit wavefront with double-shearing interferometers

In order to measure the diffraction-limit wavefront, we present three types of common-path double-shearing interferometers based on the theory of double shearing. Two pairs of half-aperture or whole-aperture wedge plates are used to introduce opposite tilt to realize the double-shearing function. By comparing the fringe widths in two fields, the marginal wavefront aberration can be obtained. In the paper, we give three different configurations: half-aperture configuration, whole-field configuration and double-interferometer configuration. The half-aperture configuration has the features of high sensitivity, stabilization and easy alignment. For the whole-field configuration, the interference fringes are displayed in two whole fields. Consequently, the divergent or convergent characteristic and aberration types of a wavefront can be identified visually. The whole-field configuration can be changed to the double-interferometer configuration for continuous test. Both small and large wavefront aberrations can be measured by the double-interferometer configuration. The minimum detectable wavefront aberration (W-0)(min) comes to 0.03 lambda. Lastly, we present the experimental results for the three types of double-shearing interferometers.

Polarization-dependent Talbot effect

The term "polarization-dependent Talbot effect" means that the Talbot self-imaging intensity of a high-density grating is different for TE and TM polarization modes. Numerical simulations with the finite-difference time-domain method show that the polarization dependence of the Talbot images is obvious for gratings with period d between 2 lambda and 3 lambda. Such a polarization-dependent difference for TE and TM polarization of, a high-density grating of 630 lines/mm (corresponding to d/lambda = 2.5) is verified through experiments with the scanning near-field optical microscopy technique, in which a He-Ne laser is used as its polarization is changed from the TE mode to the TM mode. The polarization-dependent Talbot effect should help us to understand more clearly the diffraction behavior of a high-density grating in nano-optics and contribute to wide application of the Talbot effect. (c) 2006 Optical Society of America.

Superresolution, extended focal depth or focal shift with electrically controllable radial birefringent filter

In this paper an electrically controllable radial birefringent pupil filter is proposed. It consists of two polarizers and an improved electrically controllable optical azimuth rotator which has two lambda/4 retarders, one electro-optical crystal and one radial birefringent crystal. The evolution and distribution of polarization states of this pupil filter are discussed. The most interesting and useful advantage of such a structure is that the characteristic of transverse superresolution and axial extended focal depth or focal shift can be obtained merely by controlling the applied voltage on the electro-optical crystal. The radial birefringent crystal azimuth angle cooperating with different electrical inductive phase differences will determine the transverse and axial intensity distribution. It is shown that for particular ranges of electrical inductive phase difference it is possible to obtain transverse superresolution along with extended focal depth or with a focal shift.

Phase interpretation for polarization-dependent near-field images of high-density gratings

It has been described that the near-field images of a high-density grating at the half self-imaging distance could be different for TE and TM polarization states. We propose that the phases of the diffraction orders play an important role in such polarization dependence. The view is verified through the coincidence of the numerical result of finite-difference time-domain method and the reconstructed results from the rigorous coupled-wave analysis. Field distributions of TE and TM polarizations are given numerically for a grating with period d = 2.3 lambda, which are verified through experiments with the scanning near-field optical microscopy technique. The concept of phase interpretation not only explains the polarization dependence at the half self-imaging distance of gratings with a physical view, but also, it could be widely used to describe the near-field diffraction of a variety of periodic diffractive optical elements whose feature size comparable to the wavelength. (C) 2008 Elsevier B.V. All rights reserved.

Beam splitting of low-contrast binary gratings under second Bragg angle incidence

Beam splitting of low-contrast rectangular gratings under second Bragg angle incidence is studied. The grating period is between lambda and 2 lambda. The diffraction behaviors of the three transmitted propagating orders are illustrated by analyzing the first three propagating grating modes. From a simplified modal approach, the design conditions of gratings as a high-efficiency element with most of its energy concentrated in the -2nd transmitted order (similar to 90%) and of gratings as a 1 x 2 beam splitter with a total efficiency over 90% are derived. The grating parameters for achieving exactly the splitting pattern by use of rigorous coupled-wave analysis verified the design method. A 1 x 3 beam splitter is also demonstrated. Moreover, the polarization-dependent diffraction behaviors are investigated, which suggest the possibility of designing polarization-selective elements under such a configuration. The proposed concept of using the second Bragg angle should be helpful for developing new grating-based devices. (C) 2008 Optical Society of America.