Quasi-Dammann grating with proportional intensity of array spots for surface hardening of metal

For surface hardening of metal,a quasi-Dammann grating (QDG) is proposed and fabricated to generate array spots with proportional-intensity distribution.To get uniformly hardened band distribution and improve the wear resistance of the sample surface,a three-order QDG is designed to produce array spots with enhanced intensity in the edge.The design and fabrication of the QDG are described in detail.The surface profile of the fabricated grating was measured,which shows that the fabrication error is less than...     

Application of a Phase-grating Beamsplitter in Laser-Processing Indium-Tin-Oxide Films for Liquid Crystal Panels

Array illumination built on a binary phase grating with a green, Q-switched, pulse Nd:YAG laser is used for patterning indium-tin-oxide films into electrodes of liquid crystal display panels. To this end, even-fanout gratings are recursively designed by simulated-annealing algorithm and are realized in quartz glasses by dry etching. While an array of identically intense beam spots strikes the film, a table supporting the film moves in a direction orthogonal to said spots array at a constant speed, forming a large group of equispaced grooves in the film. A machining yield of 1600 mm/s has been attained using a 32×1 grating.To whom correspondence should be addressed     

Combined optical dispersion by prism and arrayed waveguide grating with multiple diffraction orders for Raman spectrometer

A compact dispersive device for Raman spectrometer was proposed to achieve a spectrum resolution below 0.55 nm in the spectral range of 800 to 1000 nm. A 41-channel arrayed waveguide grating (AWG) with eleven different diffraction orders was designed, and each output channel of this AWG contained eleven light signals with periodically 20 nm spaced wavelength. These signals were further cross-dispersed by a prism, and finally form a 41 × 11 spots array on a CCD. The detailed theoretical analysis and simulation of this dispersive device were introduced in this paper. Compared with commercial dispersive modules composed of grating, lens, and mirrors, the proposed structure is able to provide a compact device with higher spectrum resolution, which is attractive for handheld Raman spectrometer.     

Magnetization reversal of micropattern Fe bar array: Combination of vector and Bragg magneto-optical Kerr effect measurements

We report on a magneto-optical Kerr effect (MOKE) investigation of alternating wide and narrow Fe bars, forming a two-dimensional periodic array. The magnetization reversal was studied by regular longitudinal Vector-MOKE in specular geometry as well as in Bragg-MOKE geometry, using the diffraction spots from the grating for hysteresis measurements. With Vector-MOKE a two-step switching process for the wide and narrow Fe bars is observed, indicative for a narrow switching field distribution in this array. In addition, hysteresis loops were determined as a function of the diffraction order for the hard and easy axis direction. The loops at different orders of diffraction can qualitatively and quantitatively be described by Fourier transformations of micromagnetic simulations.     

Fabrication of grating structures by simultaneous multi-spot fs laser writing

Two-photon polymerisation is an established technique for the fabrication of three-dimensional microstructures. To date structures have mostly been developed using single beam serial writing. A novel approach to simultaneous multi-spot two-photon polymerisation, that uses a SiO₂ on glass Fraunhofer diffractive optical element to generate an array of beamlets, is described. A Ti:sapphire laser, with wavelength 790 nm, 80 MHz repetition rate, 100 fs pulse duration and an average power of 25 mW, was used to initiate two-photon polymerisation. The DOE, in combination with a high power microscope objective, efficiently transforms the laser beam into a linear array of four spots of equal intensity. The fabrication of a periodic transmission grating, using parallel processing with these four spots, is shown. The grating was written in a Zr-loaded resin prepared on a glass substrate using dip coating deposition of a Zr/PMMA hybrid prepared by the sol-gel method. The operation of the diffractive element and the performance of the diffraction grating are also discussed.     

A gradient method for design of multiorder varied-depth binary diffraction gratings

A method for the design of perfectly conducting varied-depth binary diffraction gratings is proposed. The design uses the rigorous modal expansion method and is based on the gradient search algorithm for optimization of grating structure from the condition of the generation of a desired array of diffraction orders. The designs of varied-depth binary gratings with equal order intensities are reported with an efficiency of more than 90% and root-mean square errors of 2–7%.     

大公差宽容度矩形孔准周期阵列实现对高阶衍射的有效抑制

传统光栅的基础研究和应用研究进展一直备受关注。然而,高阶衍射污染使传统光栅获得的光谱纯度受到严重影响。为了抑制高阶衍射贡献,人们提出了许多单级或准单级光栅的设计方案,但它们对高阶衍射的抑制效果不可避免地受到加工精度的限制。提出了一种准周期矩形孔阵列光栅,通过优化矩形孔的概率密度分布函数,获得了比以往设计更大的加工误差宽容度。对这种光栅的衍射特性进行了分析研究。理论计算表明,即使孔径相对误差超过20%,光栅也可以完全抑制二阶、三阶和四阶衍射,五阶衍射效率与一阶衍射效率之比小于0.01%,大大降低了对加工精度的要求。     

Spectral hole burning for pulse repetition frequency analysis

We demonstrate an optical processor based on spectral hole burning (SHB) that maps the carrier frequency into the time domain and the pulse repetition frequency (PRF) into the spatial domain by illuminating an SHB crystal with a signal beam that is scanned by a tilting mirror across a slice of the crystal. This time-to-space mapping makes it possible to measure signal envelopes with a resolution of . A signal with a pulsed envelope engraves a vertical absorption grating with a spatial periodicity given by the product of the PRF and the scan velocity. Reading the grating, which the crystal stores for up to T₁, with a collimated beam yields orders diffracted at angles proportional to the PRF, which are Fourier-transformed to produce spots displaced from the DC position by distances proportional to the PRF. Increasing the PRF increases the grating periodicity, causing the diffracted spots to move away from the DC position.     

等腰闪耀光栅的相位补偿设计

设计了一种新型同面相位补偿型等腰闪耀光栅。等腰设计保证了正负衍射级对称分布在光栅法线两侧;通过优化设计同面相位补偿槽的大小,可使衍射能量向中间级次转移,只保留两个衍射极大值方向,抑制0级和高衍射级能量分布,避免能量的浪费．而且降低了高衍射级次光线因刻线阻挡导致的散射噪声,解决了加工对准与多次衍射的难题。通过理论建模和计算机仿真．分析了与反面相位补偿等腰闪耀光栅的差异,绘制了典型的衍射光强分布图。另外,还探讨了这种新型等腰闪耀光栅的灰度掩模二元光学加工方法。     

Generation of achromatic and propagation-invariant spot arrays by use of continuously self-imaging gratings

A particular class of Montgomery's self-imaging objects that we call continuously self-imaging gratings (CSIG's) is introduced. When they are illuminated by a plane wave, these objects produce a field whose intensity profile is a propagation- and wavelength-invariant biperiodic array of bright spots. The mathematical construction of these objects and their intrinsic properties are described. On a practical level, CSIG's are compact and achromatic nondiffracting array generators. We show that a good CSIG approximation can be realized by a two-level phase grating that is experimentally tested.     

Coherent micromirror arrays

A one-dimensional, spatial light phase modulator consists of a coherent array of programmable micromirrors. Each micromirror has rotation as well as elevation control to permit high-fidelity, piecewise linear approximations to a desired spatial phase profile. We demonstrate programmable, coherent spatial modulation by configuring a four-micromirror array to act as a blazed diffraction grating, showing five diffraction orders. In sharp contrast, adjustment of each mirror elevation converts the grating into the equivalent of a single, large tilted mirror that reflects only in a new specular direction. Higher-order diffraction is effectively suppressed.     

点阵绝对相位彩色多频光栅傅里叶变换轮廓术

提出一种将三角法测距与多频光栅相结合的方法,充分利用数字投影的RGB通道,将多频光栅与点阵同时投影在物体表面,综合控制受高度调制的相位信息的提取,最终获取物体的三维形貌。仿真结果显示,在高度跳变使高频光栅位移达102量级个周期时,可以准确还原原始形貌。通过实验验证,本方法能够同时复原169mm的陡峭高度跳变以及3mm的微小细节,提高了传统双频光栅的性能,具有处理较大截断面和保证细节部分的测量能力,较好地改善了傅里叶变换轮廓术(FTP)的应用性能。     

High-efficiency arrays of any desired optical beams using modified grating-based elements

High efficiency grating-based diffractive elements were previously proposed in order to generate desired arrays of various optical beams. The elements enable us to generate a diversity of arrays of optical beams in desired shapes, so that the arrays produced by the method are homogeneous, uniform and lacking of unwanted higher diffraction orders. In this technique a modulated grating is used to restructure Fresnel zone plate or zone plate-based elements to get modified grating-based elements. To examine the method, a variety of rectangular arrays of optical spots and annular beams are created by the ordinary and modified elements. It is shown that the arrays generated by the modified elements are much more uniform than the same arrays produced by the ordinary ones. In addition to the uniformity of the arrays, the unwanted higher diffraction orders are also totally eliminated. This article exploits simulation and experimental studies in order to demonstrate the functionality of the proposed technique as a multi functional high-efficiency beam shaping.     

Thin and thick diffraction gratings: Thin matrix decomposition method

A brief review of the properties of transmission diffraction gratings is presented. Two types of gratings will be analyzed: thin and volume gratings explaining how the efficiency of the different orders that propagate inside the gratings can be calculated in both cases. For thin diffraction gratings the so-called amplitude transmittance method is applied in order to get the amplitude of the different orders, whereas in the case of volume gratings more complex methods are needed, such as Coupled Wave or modal theories. We will comment on the thin matrix decomposition method (TMDM), firstly proposed by Alferness, which gives a very intuitive approach and connects the properties of thin gratings to the properties of volume ones. The thin matrix decomposition method consists in dividing the volume grating in a number of thin gratings and applying the amplitude transmittance method to each thin grating. In this way the output of a grating will be considered as the input of the next and any individual grating can be treated by the amplitude transmittance method. The novelty of this work is that a comparison is made between the analytical expressions obtained by Alferness using the TMDM with the numerical results obtained using the coupled wave (CW) and rigorous coupled wave (RCW) theories for the efficiencies of the zero, first and second order when a plane wave incides onto a sinusoidal diffracion grating at the second on-Bragg replay angular condition.     

复合Ag/SiO_2正弦光栅基底SERS特性分析

当前微流控表面增强拉曼散射(SERS)检测领域常用的贵金属纳米颗粒溶胶单位体积内热点区域数量有限且热点区域范围较小,而贵金属纳米三维阵列结构加工时间长,成本高昂并存在"记忆效应"。本文提出了集成到微流道的复合Ag/SiO_2正弦光栅SERS基底结构,可以利用激光干涉光刻技术进行制备,无需预制掩膜版,可实现大面积、低成本SERS基底简易快速制备。利用严格耦合波分析方法(RCWA)建立了复合正弦光栅表面电场增强数学评估模型,推导了表面等离子体共振(SPP)耦合吸收率数学模型,分析了入射光、复合正弦光栅结构与外界环境介电常数的优化匹配关系,得到了入射光785 nm条件下的最佳复合正弦光栅结构。通过制备加工并实验验证了复合正弦光栅的SERS性能,SERS增强因子(EF)能够达到10~4。     

Circular Dammann grating

A circular Dammann grating that can produce circular equal intensities at various orders in the far field is described. A set of parameters such as order, circular number, uniformity, and diffraction efficiency has been defined to describe the novel diffractive phase elements. Numerical solutions of binary-phase (0, pi) circular Dammann gratings are given. The results of experiments with a four-order circular Dammann grating made by a lithographic technique are presented. This novel diffractive optical element should be highly interesting in a wide variety of practical applications.     

一种液晶相位调制特性的测量方法

提出一种基于衍射光栅的液晶相位调制特性测量方法.该方法利用液晶构建相位分别为0和φ的二值光栅,通过傅里叶光学的方法推导衍射光栅第0级衍射光斑光强和调制相位φ之间的关系,然后实测光强和液晶驱动电压之间的对应关系来得到相位和液晶驱动电压之间的对应关系,即液晶相位光栅的相位调制特性.最后利用测量相位调制特性结果构建液晶相控阵,用光束偏转误差验证调制特性测量结果,相位测量误差小于1×10~(-3)rad.     

亚波长光栅的偏振闪耀特性

 使用琼斯矩阵的方法推导了连续结构亚波长光栅的衍射方程,给出了光栅衍射效率表达式,对偏振特性与衍射特性进行了研究。发现连续结构亚波长光栅仅存在３个衍射级,总衍射效率为100%,且衍射效率可在衍射级间任意分配,0级的偏振态与入射光的偏振态相同,±1级衍射光偏振态与入射光无关,－1级为左旋圆偏振光,＋1级为右旋圆偏振光。通过设置入射光偏振态与光栅相位延迟等参数,可使光栅具有闪耀特性,据此可用于设计高效偏振光分束器和偏振光开关。     

平场光栅谱仪相对衍射效率测量

 以激光碳等离子体作为软X射线源,同时用平场光栅谱仪、常栅距光栅谱仪测量了类氢和类氦离子谱线强度,以一级谱线强度为标准,给出了平场光栅谱仪高级次光谱的相对衍射效率。     

Strong coupling of a surface-relief dielectric grating to a structurally chiral volume grating

The boundary-value problem of the reflection and transmission of light by a composite structure, wherein a surface-relief dielectric grating is coupled to a structurally chiral volume grating, has been formulated and solved with results showing the robust co-existence of phenomena characteristic of both types of grating: namely, Rayleigh–Wood anomalies and Bragg phenomena. A mechanism to strengthen the coupling between both grating types is included – namely, a quarter wave plate – whose birefringence converts normally incident linearly polarised light at the Bragg wavelength into transmitted circularly polarised light (and vice versa). It is possible to tailor the period of the sinusoidally corrugated surface-relief grating such that the scattering of obliquely incident light from above, by the surface grating, will lead to a specific non-specular order being scattered onto a path which is normally incident on the rest of the composite structure. Significantly, such orders exhibit the circular Bragg phenomenon in reflection and transmission only if both grating types are present, making this a “truly” coupled effect.