利用双光栅的多普勒频移测速度

衍射光的多普勒频移是与光栅运动速度有关的量.激光束依次通过动光栅、静光栅衍射,然后使1对光频不同、彼此平行又能部分重叠的衍射光束通过硅光电池进行光电转换,得到的信号电流的频率等于多普勒频移.信号电流经I/V转换、f/V转换和A/D转换后,由单片机测出电压,由此就可以确定动光栅的运动速度.最后对利用双光栅的多普勒频移测气垫导轨上滑块的速度进行分析和讨论.     

Displacements and deformations of a vortex light beam produced by the diffraction grating with embedded phase singularity

Properties of vortex light beams produced by a diffraction grating with groove bifurcation (“fork” structure) are studied in the case of small diffraction angles. Analytical expressions are derived for the amplitude distribution of a diffracted beam generated from an incident Gaussian beam with arbitrary radius and wavefront curvature, transversely shifted and inclined with respect to the nominal axis (normal to the grating crossing it at the bifurcation point). In such situations, the output beam becomes asymmetric; the optical vortex core and the intensity maximum displace orthogonally to the incident beam shift direction. The nearest vicinity of the vortex core preserves its circular symmetry and the optical vortex remains locally isotropic. The effects of misalignment depend on the incident beam characteristics, the diffraction order and the propagation distance behind the grating. Experimental measurements support the results of calculations.     

高斯光束经环形光栅的衍射特性分析

基于傅里叶-贝塞尔变换计算高斯光束垂直入射环形光栅时的衍射远场分布,分析了其衍射远场光强分布的一般规律,并与平面波入射时的情况进行了比较.计算结果表明：当光栅半径为1.5倍高斯光束束腰半径时, 随着光栅环数的增加,中央亮斑半值全宽先减小后增大、中央亮斑所包含的功率占总功率的比值减小、中央主极大光强值减小,三者的变化趋势与平面波入射时的趋势一致;中央亮斑半径、次极大光强值变化趋势与平面波入射时的变化趋势不同.当环数小于5时,高斯光束经过环形光栅的衍射场光强变化无规律;当环数大于10后两种情况下衍射场光强变化都不明显;当环数趋于无穷时中央亮斑半径、中央亮斑半值全宽、次极大光强值趋于圆孔衍射(环数等于1)时的值,中央亮斑所包含的功率占总功率的比值约等于圆孔衍射时的1/2,中央主极大光强值约等于圆孔衍射时的1/4.     

反射型体全息光栅对超短脉冲激光光束衍射的性质

在光栅记录介质色散效应的影响下,拓展Kogelnik的耦合波理论研究了反射型体全息光栅对偏振方向垂直和平行于入射面的超短脉冲激光光束衍射的性质。结果表明对于记录在LiNbO3光折变晶体中的体全息光栅,在色散效应、光栅参量和入射条件的共同影响下,光栅对偏振方向垂直于入射面的超短脉冲激光光束衍射的光谱带宽大于对偏振方向平行于入射面的超短脉冲激光光束衍射的光谱带宽,在不考虑光栅介质色散效应的影响时,它们都变大。进一步给出了衍射光的光谱带宽及光栅的衍射效率随入射脉冲的光谱带宽与光栅的光谱带宽比值的变化情况。     

光学马格努斯效应中的横向角移分析

从平面角谱理论出发,建立了光束在空气和玻璃界面折射的传输模型.基于这一模型,揭示了光学马格努斯效应中的横向角移现象.对于特定的线偏振和椭圆偏振光束,其折射场重心出现了横向角移,而当入射光束为圆偏振时,横向角移则会消失.在正负折射率界面,光束的横向角移产生了反转现象,这是由于光束在左手材料中发生了负衍射.超高折射率可明显地减少横向角移,而超低折射率则可显著地增强横向角移.这些发现将为如何调控和增强光学马格努斯效应提供理论依据. 关键词： 光学马格努斯效应 横向角移 圆偏振     

Millimeter wave beams diffracted from reflecting gratings

According to the angular-spectrum method, a radiation beam of an antenna horn in the Fresnal region is decomposed into the plane waves with the fast Fourier transform algorithm and the waves diffracted from a reflection grating are superposed as a diffracted beam. Compared with the reflected beam from the same size mirror, the radiation half width of the diffracted beam from a grating is narrower and its lateral shape is shift. These performances have been experimentally verified at Ka-band by: (1). The relative diffraction efficiencies in the first order with two triangular gratings which is put along propagating direction of a beam produced by a conical lens-horn. (2). H-plane lateral width with power—3dB lapsed of the focus beam from a grating and a mirror in a grating spectrometer for millimeter waves (25–100 GHz).     

Implications of spectral hole burning on the manipulation of spatial Goos–Hänchen shift in an atomic cell

We present a new scheme to report on Goos–Hänchen (GH) shift experienced by the Gaussian light beam interacting with an optical cavity filled with four-level sodium atomic medium in the spectral hole burning region with and without Doppler broadening effect. Theoretical atomic density-matrix formalism is employed to obtain the susceptibility of atomic medium while the stationary-phase-theory is used to compute the GH shift in the reflected and transmitted probe beams subjected to control fields. A steep normal slope of dispersion is observed with a maximum and zero probability of transmission and reflection coefficients, respectively, at the regions of the spectral holes burning. In the normal dispersion spectrum at the region of spectral hole burning, positive and negative GH shift is observed, respectively, in the transmitted and reflected light beams. However, at anomalous dispersive regions negative GH shift in the transmission beam and positive GH shift in the reflection beam is observed. The reflection and transmission coefficients as well as the spatial GH shift are the functions of probe detuning, collective phase of control fields, beam incident angle and inverse Doppler broadening effect in the spectral hole burning region. The position and number of spectral holes also depend on the same spectral parametrs as stated above. The study is expected to be useful for optoelectronic devices and optical-clocking applications.     

Diffraction of light by two spatially separated parallel ultrasonic waves of different frequency

A theory is developed for the diffraction of light by two spatially separated parallel ultrasonic progressive waves of different frequency. The preliminary theories ofRaman andNath [C. V.Raman and N. S.Nath, Proc. Indian Acad. Sci. A2, 406–412; 413–420 (1935)] for normal and oblique incidence are taken to be valid. The resulting equations are extensions of earlier results of R.Mertens, Z. Physik160, 291–296 (1960). The predicted periodicity of the diffraction spectrum with increasing sound beam separation agrees with the well known periodicity of the light intensity distributions in the Fresnel zone of the phase grating formed by the first ultrasonic wave. Results of numerical calculations are presented to illustrate features of the theoretical results, as reflected in the first order of diffraction for 3.0 and 6.0 Mc ultrasonic waves in water.     

Consequences of the Kramers-Kronig relations for light diffraction on thick gratings

Diffraction of monochromatic light on a grating leads to the attenuation of the transmitted beam of diffraction order zero. In the case of a thick grating the diffraction efficiency, and hence the effective attenuation coefficient, is a fast-varying function of the Bragg mismatch angle. According to Kramers-Kronig theory, the transmitted beam encounters a phase shift that also depends on the mismatch angle. This phase shift is measured for holographic gratings in a photoaddressable block copolymer and compared with analytical calculations.     

畴腐蚀掺镁铌酸锂可调阵列光分束器的研究

研究了不同畴腐蚀深度的掺镁铌酸锂二维六角可调阵列光分束器的分数Talbot效应.对不同Talbot分数β和不同畴腐蚀深度的阵列光分束器Talbot衍射像进行了数值模拟理论研究.模拟结果表明,Talbot分数β可以改变Talbot衍射像的周期及结构分布,而畴腐蚀深度可有效调制衍射像的光强分布.在理论研究的基础上,设计并制备了具有不同畴腐蚀深度的掺镁铌酸锂二维六角阵列光分束器,对其在不同Talbot分数β条件下的分数Talbot效应进行了通光实验研究,实现了畴腐蚀阵列光分束器对近场Talbot衍射光强分布的调制,实验结果与理论研究结果一致.     

菌紫质同线偏振全息记录时再现光偏振方向对衍射效率的调制

当用相同偏振方向的物光和参考光在菌紫质薄膜上记录光栅时,再现光的偏振方向会影响其衍射效率.采用琼斯矩阵方法对此进行了理论分析,结果显示,再现光的偏振方向对衍射光的光强产生余弦调制;当再现光的偏振方向平行或垂直于记录光的偏振方向时,衍射光仍为线偏振光,其他情况下衍射光均变成椭圆偏振光.再现光偏振方向对衍射效率峰值的调制为正向余弦调制,对衍射效率稳定值的调制为反向余弦调制(与前者在相位上相差π).加入辅助紫光可抑制光栅的饱和,从而使得再现光偏振对衍射效率稳定值的调制由反向余弦调制变为正向余弦调制,并且提高了衍 关键词： 菌紫质 光致各向异性 衍射效率 琼斯矩阵     

A simple method for testing laser beam collimation

A simple and improved method is proposed for testing laser beam collimation by a new type of grating, comprising concentric equilateral triangles and the mirror images of these triangles. Although this type of grating possesses one-dimensional periodicity in a particular direction and inherent defects in periodicity, the moiréfringe pattern formed by placing an exact replica of such a grating at its self-imaging plane shows that the self-imaging phenomenon takes care of the defects in the periodic objects.     

基于微机电系统光栅平动式光调制器实验和优化设计

基于微机电系统(MEMS)的光栅平动式光调制器(光栅平动式光调制器)调制性能的实验研究关系到其进一步应用。设计了光栅平动式光调制器的相干光学信息处理系统实验方案,He-Ne激光器出射的光束经扩束器和准直透射后成为平行光入射光栅平动式光调制器,被测光栅平动式光调制器放置在相干光学信息处理系统的输入面,滤波器在频谱面上,显微镜放大像面上的信号,经CCD在计算机上记录存储;实验结果和理论分析吻合。对光栅平动式光调制器进行方案优化,将可动光栅边框和悬臂梁表面处理成不反光,使可动光栅和下反射镜构成的整个反射面为光栅周期的整数倍。经理论计算,在光栅周期为8μm,光栅占空比为0.5,光栅边距为2μm,周期数为6的条件下,光栅平动式光调制器图像填充率为74.67%,光学效率为81.06%,衬比度大于5000∶1。     

On-line beam diagnostics based on single-shot beam splitting phase retrieval

We propose a novel on-line beam diagnostic method based on single-shot beam splitting phase retrieval. The incident beam to be measured is diffracted into many replicas by a Dammann grating and then propagates through a weakly scattering phase plate with a known structure; the exiting beams propagate along their original direction and form an array of diffraction patterns on the detector plane. By applying the intensity of diffraction patterns into an iterative algorithm and calculating between the grating plane, weakly scattering plane, and detector plane, the complex field of the incident beam can be reconstructed rapidly; the feasibility of this method is verified experimentally with wavelengths of 1053 and 632.8 nm.     

渐变周期弯曲光栅的衍射和成像特性

阐述了渐变周期弯曲光栅的原理,对其衍射特性和成像特性进行了分析,结果表明:渐变周期弯曲光栅具有分束和聚焦的双重作用;其对称衍射级起到焦距相等的正透镜和负透镜的作用;它可把不同景深的的物体聚焦成像于空间分离的同一焦面上.     

Two-dimensional higher-diffraction-order optical beam splitter based on phenanthrenequinone-doped poly(methyl methacrylate) photopolymer

A two-dimensional optical beam splitter has been realized that uses the higher diffraction orders of a refractive-index grating. Gratings were recorded experimentally with light from a semiconductor laser incident at a small angle on phenanthrenequinone-doped poly(methyl methacrylate) photopolymer. The incident signal beam, which was made up of three different wavelengths (632.8, 532.0, and 488.0 nm), was split by the grating into multiple output beams with nearly equal size and separation. Results are given for when the sample grating was placed behind, in front of, and in the focal plane of a Fourier lens. The properties of higher-order-diffraction images have been discussed. The discussion shows that a two-dimensional higher-diffraction-order optical beam splitter provides a practical method for splitting a signal beam.     

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.     

任意偏振态光束全反射时的侧向和横向位移

光束在电介质界面发生全反射时,实际反射光束会在入射面内相对于几何反射光束产生一侧向位移,在垂直于入射面的方向产生一横向位移。利用改进的能流法研究了任意偏振态光束发生全反射时的侧向和横向位移特性。研究表明,侧向位移的大小与入射光束的两组成部分———TE和TM偏振光的相位差无关,而与两组分的光强比密切相关,且该位移可以表示为TE和TM偏振光束各自的位移按光强的加权平均。横向位移的大小不仅与入射光束两组分的光强比相关,还与组分的相位差密切相关。另外,反射光束不仅在椭圆偏振态入射的情况下会产生横向位移,而且在TE和TM偏振态之外的其他线偏振态入射时,也会产生横向位移。     

光纤激光器频谱组束的理论研究

 建立了由光纤激光器阵列、薄透镜和衍射光栅组成的频谱叠加理论模型，基于高斯光束的变换和衍射理论，推导出远场光强分布的关系式，探讨了系统参量的优化设计并进行了数值模拟。结果表明：当中心波长激光器的-1级干涉主极大与槽面衍射主极大重合、零级干涉主极大刚好落在槽面衍射的+1级零值极小上、其它波长激光器的-1级干涉主极大与中心波长激光器的槽面衍射主极大重合时，输出光束的衍射效率较高；当光栅平面法线与薄透镜光轴的夹角为衍射光栅槽形角的一半时，输出光束的半角宽度较小。     

Interferometric testing of the spacing error of a plane diffraction grating

Two measuring methods of the plane diffraction grating spacing error are presented in this work. The first one resembles real- time holographic interferometry. The hologram is exposed when an object beam is the nth diffraction order, and is then illuminated by the -nth diffraction order wave. The second method makes use of double-exposure holographic interferometry. The first exposure is performed when the nth diffraction order is an object beam. During the second exposure the -nth diffraction order is an object beam. Both methods allow to measure the spacing error separately, not only from the grating surface error but also from the aberrations introduced by the other optical elements of the set-up.