适用于单色脉冲光的新型双光楔晶体退偏器

针对单色脉冲光的退偏振应用,对传统双折射晶体退偏器存在的局限性进行分析,提出了一种新型的双光楔晶体退偏器。此退偏器由2个光轴互相成π4并设计成特殊楔形的石英晶体光楔组成,理论计算结果表明此退偏器能对单色脉冲光完全退偏。基于光学设计软件(A SAP)对所设计的退偏器进行了仿真计算,结果表明经此退偏器退偏后的出射光偏振度P0.001 26。此退偏器的特点是对于任意偏振态的单色入射光都能实现有效的退偏,也适用于对准单色光进行退偏,且退偏效果与时域无关。     

2 μm Cr,Tm,Ho:YAG激光热退偏效应的数值模拟及实验研究

理论分析了Cr,Tm,Ho:YAG激光晶体的热退偏效应, 模拟计算了该晶体棒端面退偏度的分布, 并进行了偏光干涉实验验证. 结果表明, 数值模拟和实验研究结果完全一致, 热致退偏效应随抽运能量增大而增强, 退偏度分布呈十字形, 最大退偏度发生在晶体棒端面上与起偏器偏振方向成45°方位处. 以此提出了高能量Cr,Tm,Ho:YAG激光器的热退偏补偿方法, 获得了激光脉冲能量提高24%以上的实验效果.     

星载光栅成像光谱仪的退偏器设计与分析

星载光栅成像光谱仪中的光栅通常有着强烈的偏振响应,为保证成像光谱仪测量结果的准确性,加入退偏器是消除光学系统的偏振响应的一种常用方法.对水平-垂直(H-V)型石英退偏器的退偏原理进行了理论分析,根据成像光谱仪的偏振响应特点,采用一片H-V型石英退偏器即可实现光谱仪的退偏要求.重点分析了退偏器引入的双像对成像光谱仪像质的影响,分析的结果表明,加入退偏器后,仪器偏振响应敏感度小于1%,MTF下降小于1.5%,像质满足使用要求,完全可应用于星载光栅成像光谱仪.     

波片和旋转器的复合退偏效应研究

介绍了几种退偏器,并详细论述了复色光的退偏机理.用Stockes矢量和Mueller矩阵分析了波片和旋转器组合对复色光的退偏效应,导出了Stockes矢量的具体形式,并对复色光的退偏进行了讨论,所得结论对偏光器件的设计与应用均具有一定的价值.     

光谱仪会聚光路中退偏器的设计方法

为了降低光谱仪的偏振敏感度,提出了一种在会聚光路中设计退偏器的方法。该方法首先将系统的望远镜和准直镜视为辅助光路,使得光束的偏振状态可以用Stocks矢量来表示;然后使用Mueller矩阵来表示元件的偏振特性,并推导出了基于Mueller矩阵的系统偏振敏感度模型;最后利用多重多元回归分析来提升Mueller矩阵的计算速度与精度。基于该方法设计了一款放置在会聚光路中的改进型退偏器,系统的偏振敏感度小于1%,像点分裂距离小于8μm,该结果满足设计要求,验证了该方法在会聚光路中设计退偏器的有效性。     

2.94 μm Er:YAG激光热效应数值模拟及实验研究

理论分析了Er:YAG激光晶体的热退偏效应,模拟计算了该晶体棒端面退偏的分布,并进行了偏光干涉实验验证。结果表明,数值模拟和实验结果完全一致,热退偏效应随抽运能量增大而增强,退偏分布呈十字形,最大退偏发生在晶体棒端面上与起偏器偏振方向成45°方位处。同时,还阐明了一种利用临界稳定腔来测量灯抽运脉冲Er:YAG激光器有效热透镜焦距的简单方法,测量出不同抽运功率下Er:YAG晶体的等效热焦距。     

基于SPGD算法的非保偏-保偏光自适应偏振转换

报道了一种基于随机并行梯度下降(SPGD)算法的高消光比非保偏-保偏光自适应偏振转换系统。该系统利用偏振控制器对非保偏光的偏振分量进行直接控制,通过SPGD算法对输出的偏振消光比进行优化,最终实现了自适应的非保偏-保偏光的偏振转换。理论上,结合SPGD算法和偏振控制器的原理,对系统进行分析,建立了非保偏-保偏光自适应偏振转换的数学模型。实验上,利用该系统实现了非保偏到保偏光的转换,获得了14.1dB的线偏振光输出;并利用该系统将任意方向(0~360°)偏振态的线偏振光转换为期望偏振态的高消光比线偏光,其输出线偏光的平均消光比约为12dB。     

Zig-Zag板条的全反射退偏分析

利用菲涅尔公式分析了Zig-Zag板条中全反射退偏对谐振光束的影响和能量损耗。分析了当谐振光偏振方向与Zig-Zag板条的选偏方向存在偏差时,线偏光经过板条后的偏振态,并计算了各因素对Zig-Zag板条全反射退偏损耗的影响。根据板条全反面的镀膜特点设计合理的谐振光全反射次数可有效地降低Zig-Zag板条的全反射退偏损耗。     

Zig-Zag板条的全反射退偏分析

利用菲涅尔公式分析了Zig—Zag板条中全反射退偏对谐振光束的影响和能量损耗。分析了当谐振光偏振方向与Zig-Zag板条的选偏方向存在偏差时,线偏光经过板条后的偏振态,并计算了各因素对Zig—Zag板条全反射退偏损耗的影响。根据板条全反面的镀膜特点设计合理的谐振光全反射次数可有效地降低Zig—Zag板条的全反射退偏损耗。     

石英光楔退偏振器研究

本文对石英光楔作为退偏振器的原理、设计及有效性进行了理论分析和实验研究,指出了最佳退偏条件。     

Simple depolarizers for spectrophotometric measurements of anisotropic samples

Spectrophotometric measurements on optically anisotropic samples are considerably affected by the partial polarization of light in the instrument. It is shown that by depolarizing the incident beam, more realistic results are obtained even for strong directional anisotropic materials. Two types of depolarizers were investigated.     

Dependence of extinction cross-section on incident polarization state and particle orientation

This note reports on the effects of the polarization state of an incident quasi-monochromatic parallel beam of radiation and the orientation of a hexagonal ice particle with respect to the incident direction on the extinction process. When the incident beam is aligned with the six-fold rotational symmetry axis, the extinction is independent of the polarization state of the incident light. For other orientations, the extinction cross-section for linearly polarized light can be either larger or smaller than its counterpart for an unpolarized incident beam. Therefore, the attenuation of a quasi-monochromatic radiation beam by an ice cloud depends on the polarization state of the beam if ice crystals within the cloud are not randomly oriented. Furthermore, a case study of the extinction of light by a quartz particle is also presented to illustrate the dependence of the extinction cross-section on the polarization state of the incident light.     

Writing 40 nm marks by using a beaked metallic plate near-field optical probe

We have developed a near-field optical probe that uses a triangular metallic plate with a three-dimensionally tapered apex as a light source for thermally assisted magnetic recording. Numerical analysis using a finite-element method shows that the size of the optical spot generated at the apex is 15 nm x 20 nm, and the efficiency (defined as the ratio between the power of the optical near field at the surface of the recording medium and that of the incident light) is 15% when the incident light is focused by a lens with a numerical aperture of 0.8. The metallic plate was fabricated on the surface of a quartz slider and used for writing marks on a phase change recording medium. The marks were observed with a scanning electron microscope, and we confirmed that marks with a diameter of 40 nm were successfully written on the medium.     

Long-range correlations of the polarized-light intensity in disordered samples

The spatial correlation function of intensity fluctuations in a speckle formed by polarized light multiply scattered in a disordered sample has been calculated. The dependence of the long-range spatial correlations on the polarization state of incident light and the depolarizing properties of the medium has been determined for the cases of transmission and reflection.     

Polarization characteristics and magneto-optic diffraction efficiency at oblique light incidence

In a great number of papers that deal with the study of the magneto-optic diffraction (MOD), theoretical analysis and interpretation of experimental data are performed without regard for reflection effects of the incident and diffracted light beams on the entrance and exit surfaces of the transparent film. In consequence the MOD parameters are not connected with the angle of light incidence and the orientation of the incident light polarization plane. In the present work the reflection effects are taken into account. For the Raman-Nat diffraction region the general expressions involving the relationships of diffracted light polarization and intensity with the symmetry of the grating, angle of incidence and polarization of the incident light are obtained. In particular it is shown that even for a symmetrical grating the polarization of the zeroth-order diffracted beam differs from that of the incident light, and the polarization of higher-order beams differs from the orthogonal one providing that the incident light is not s- or p-polarized. A maximum in the angular dependence of diffraction efficiency is predicted being observed experimentally.     

星载光栅光谱仪消偏器性能研究

星载光栅光谱仪中的光栅有着强烈的偏振响应。为了保证光谱仪测定的光谱分布的准确性,必须在光辐射进入仪器光谱测量部分之前就消去光辐射的偏振。应用矩阵光学推导出了这种紫外石英消偏器的残余偏振度,并得到影响其消偏性能的几个因素。建立了一套测试系统,在300-360nm波段上对其消偏性能进行了研究,得出入射光经过紫外石英消偏器后的残余偏振度变化范围1.2%-5.7%。与理论推导有较好的一致性。并按照国际通用不确定度评估规范,对测量结果进行不确定度分析和评估,组合不确定度小于1.8%。     

Simultaneous slow and fast light in C60 solution

Recently, many researchers have reported their work about sub- and superluminal propagation. And many experiments have demonstrated the group velocity transition between slow and fast light. In this letter, the authors reported simultaneous slow and fast light in a single light beam which could be explained by the photorefractive lens-like effect and the spatial dispersion qualitatively. In our experiment, a focused light beam at 532 nm normally incident upon a thin quartz cell full of C₆₀ solution and spatial diffraction rings were observed behind the cell. Recurring to a pinhole diaphragm, we measured the group velocity of light of different position on the diffraction rings. The experimental results demonstrated that slow and fast could exist in a single beam at the same time. We could acquire slow or fast light just by adjusting the position of the detector and keeping the experimental parameters, such as: modulation frequency and incident intensity, unchanged. Our experiment put forward a new way to control the group velocity in nonlinear optical material.     

Intensification and location of relativistic laser pulses against pointing fluctuations with micro-tube plasma lenses

We analyze, via an off-axis incident model and three-dimensional particle-in-cell simulations, the influence of beam pointing fluctuations (BPFs) on the propagation properties of relativistic laser pulses in micro-tubes. It is observed that the in-tube laser intensity can be further amplified in the BPFs-induced off-axis incident case. But the intensification factor exhibits strong polarization-dependence. When the laser pulse is linearly polarized in the off-axis incident plane (p-polarization), more electrons may be dragged out from about a half of the tube inner surface in each across section than in the on-axis incident case, enhancing the effects of relativistic nonlinearity and channel focusing. The area for generating more electrons is reduced by one half in the s-polarization case, resulting in less efficient light intensification. The BPFs-induced off-axis incident also leads to pulse shortening. Moreover, light confinement in the tube core is evident and the laser pulse tends to be coaxial with the tube.     

Influence of incident light polarization on photonic nanojet

Dielectric microspheres can confine light in a three-dimensional (3D) region called photonic nanojet is shown when they are illuminated by different polarized beams. The influence of incident light polarization on photonic nanojet using the finite-difference time-domain (FDTD) method is demostrated. The axial field intensity profiles of photonic nanojets for both the linear and circular polarization incident beams are very similar. Azimuthal polarization incident beam induces a doughnut beam along the optical axis, while the radial polarization incident beam permits one to reach an effective volume as small as 0.7(λ/n) 3 .