改进的防伪全息标识衍射效率测量系统

提出一种激光全息特性参数检测方法.以不稳定度为5%的He-Ne激光器为光源,利用同一光束分成的反射光和透射光光强度比例恒定的性质,实时探测衍射光强与反射光强,得到全息防伪标识的衍射效率.给出了实际入射光强与根据反射光强计算得来的入射光强两者的对比曲线,以及对8版不同样品衍射效率的测量结果.实验数据表明:透射光强测量值相对误差不超过0.29%;衍射效率测量值相对误差最大值不超过0.81%,比原方法测量精度提高近一倍.     

无明胶重铬酸盐全息图的后处理方法

本文介绍了无明胶重铬酸盐全息记录软片(简称NGD)的感光成像机理。实验研究了NGD全息图的后处理过程对衍射效率和表面灰雾的影响,给出了处理时间与衍射效率,表面灰雾的关系曲线,提出了一种适用于这种新材料后处理的方法。     

双固化型全息用光致聚合物的研制及其全息性质研究

以环氧树脂为成膜树脂，甲基丙烯酸甲酯为光聚合活性单体，研制了一种双固化型全息用光致聚合物材料。通过成膜树脂配方的选取和光敏染料的选取优化了样片的配方组成，用457nm的蓝光在样片中记录全息光栅，用632．8nm的红光作为探针光，研究了样片的衍射效率、灵敏度、折射率调制度、预曝光量和收缩率等全息性能，测试结果表明单体的含量与组分的选取是影响样片衍射效率的主要因素，同时样片的制膜工艺对其全息性能也有很大的影响，通过配方的调整和制膜工艺的优化，部分样片的综合性能已基本达到实用化的需要。     

平面光栅衍射效率的双光束高精度测试

本文提出了一种双光束检测器测试平面光栅衍射效率的新方法，文中重点介绍了测试平面光栅绝对与相对衍射效率的基本原理和方法，导出了相应的效率计算公式，并给出实验结果。研究表明，本方法不仅能有效地消除光源波动所带来的影响，提高测试精度，而且可从根本上解决传统双光束测试中因两个探测器光谱响应的不同给自动归一化所带来的问题，因而本方法既能用于光栅衍射效率的光谱定点测试，还可实现光谱衍射效率曲线的全波段自动扫描记录。     

相位光栅衍射法测量高灰阶LC-SLM相位调制特性

为测量高灰阶液晶空间光调制器(LC-SLM)整体相位调制特性,引入二维棋盘形相位光栅衍射测量方法.根据傅里叶光学原理,经过理论推导和仿真分析得到零级衍射光强与相位调制量之间的关系.搭建含有参考光束的衍射实验系统,通过适当的光斑图像处理计算出零级衍射相对光强,从而获得相位调制特性曲线,并与干涉测量法实验结果进行对比.实验...     

反射型阶梯光栅的特性分析

衍射效率是评价二元光学器件质量性能的重要指标之一.针对反射性阶梯光栅,利用几何方法计算出斜入射情况下光束在台阶边缘的光程差的分布情况,根据多缝夫琅和费衍射推导出反射型阶梯光栅的衍射光强表达式.并在此基础上,讨论了台阶数N取2和N趋向于无穷两种极限情况下阶梯光栅光强公式的变化情况,得到区别于一般文献所表达的衍射效率公式.初步试验表明,反射型阶梯光栅的衍射效率与台阶数、蚀刻深度与入射波长的比值均有密切相关.     

激光

20年前，人们为有的商品上贴了的一枚闪闪发光的激光全息防伪标识而感到新奇，而今天的激光全息防伪技术已经运用非常广泛，人们在信赖贴有防伪标签产品的同时，也开始对利用激光防伪标识进行假冒伪劣商品行为开始警惕。那么，激光全息防伪技术还能不能起到防伪的作用？ 激光全息防伪技术属于物理学防伪范畴，包括激光全息图像防伪标识、加密激光全息图象防伪标识和激光光刻防伪技术，加密激光全息防伪标识在证卡中运用较多。编者就慧聪网上刊登的一篇文章介绍给大家，以便对激光全息防伪技术作一简要了解。     

全息光学元件中编码与象质和衍射效率的关系

以平面波束变换为十字光束的全息光学元件为例，详细分析了ＨＯＥ的相位调制、编码与解主财过程，推导出ＨＯＥ的衍射效率近似解的表达式，计算出近似条件下最佳编码最大刻蚀深度值，并且对该编码方案对ＨＯＥ成象质量的影响进行了分析，得出了分析的结果和结论，同时对衍射效率近似解表达式的误差进行了研究，并给出了分析结果。     

市场对激光全息防伪标识的新要求

模压全息技术自80年代末引进国内，已走过了近十个年头。人们对激光全息防伪标识已经认识了解，并大量使用；激光全息模压设备也从国外引进并自行制造．到目前为止，全国已有数百条生产线和激光全息模压机，形成了一定的生产规模。     

集成光栅干涉微位移测量方法

介绍了一种新型集成光栅干涉微位移测量方法,设计加工了微位移敏感芯片,并进行了初步的性能测试．敏感芯片利用硅-玻璃键合体硅工艺制作而成,在玻璃上制有金属光栅,光栅上方有由铝梁支撑的可动结构．实验系统由敏感芯片、半导体激光器、光电二极管以及相应的驱动、检测电路组成入射激光照射到光栅上产生衍射光斑,衍射光的光强随可动结构与光栅之间的距离变化,通过测量衍射光强的变化可以得到位移．测试实验结果表明,所制作的集成光栅干涉微位移敏感芯片可实现位移检测,最小可检测的位移约0．2nm．     

Diffraction efficiency and signal-to-noise ratio of diffuse-object holograms in real time in polyvinyl alcohol photopolymers

We studied the influence of the beam ratio and intensity on the optical quality of the transmission hologram images of diffuse objects stored in a photopolymer and reconstructed in real time. The signal-to-noise ratio and the diffraction efficiency were used as measures of the optical quality. We obtained a signal-to-noise ratio of 0.94 with a diffraction efficiency of 13% for a beam ratio of 20 and an intensity of 1.2 mW/cm(2).     

Calculation and evaluation of narcissus for diffractive surfaces in infrared systems

In infrared optical systems, the narcissus effect for diffractive surfaces should be calculated with specific diffraction orders based on the diffraction efficiency. It is shown in this work that the diffraction order of maximum diffraction efficiency varies with the change of the incident angle and wavelength of the backward-traced narcissus flux. Meanwhile, yni, which is the paraxial evaluation criterion of narcissus intensity for a refractive surface, is modified considering diffraction when a ray passes through diffractive surfaces, and a practical example has been given. The analysis can be used to calculate and control the narcissus intensity in infrared optical systems with diffractive surfaces.     

Evaluation of narcissus for multilayer diffractive optical elements in IR systems

The influence of narcissus effect for multilayer diffractive optical elements (MLDOEs) is evaluated from the viewpoint of diffraction efficiency and the narcissus intensity. A modified paraxial evaluation criterion for the reflected narcissus radiation of MLDOEs has been deduced. A practical 8-12 μm IR optical system designed with one two-layer diffractive element has been given to illustrate the distribution of incident narcissus energy among various diffraction orders in the waveband. The narcissus intensities of the two diffractive surfaces have been calculated for those diffraction orders that have the maximum diffraction efficiency. This method can be used in the process of evaluation and control of the narcissus influence in IR optical systems with MLDOEs.     

Improving binary phase correlation filters using iterative techniques

An iterative technique has been used to improve the design and performance of the binary phase version of a tandem-component correlation filter. The results are compared to a regular matched filter, a phase-only filter (POF), and a binary phase POF, in terms of optical efficiency, SNR, and peak correlation intensity.     

Characterization of photopolymerization by a holographic technique applied to a scattering hydrogel

A holographic technique, which consists of writing a phase grating onto a photopolymer layer and recording the time evolution of its diffraction efficiency, is presented for a scattering hydrogel. The influence of photopolymer thickness and writing laser intensity is investigated. Writing parameters that yield maximum diffraction efficiency are determined. A thickness greater than 1/3 of the scattering length results in the diffusion of light in the sample, leading to a decreased diffraction efficiency of the grating. This behavior can be explained by a combination of chemical diffusion and optical scattering. Finally, a calibration of diffraction efficiency with respect to a gel and sol fraction is presented.     

Zone-boundary optimization for direct laser writing of continuous-relief diffractive optical elements

Enhancing the diffraction efficiency of continuous-relief diffractive optical elements fabricated by direct laser writing is discussed. A new method of zone-boundary optimization is proposed to correct exposure data only in narrow areas along the boundaries of diffractive zones. The optimization decreases the loss of diffraction efficiency related to convolution of a desired phase profile with a writing-beam intensity distribution. A simplified stepped transition function that describes optimized exposure data near zone boundaries can be made universal for a wide range of zone periods. The approach permits a similar increase in the diffraction efficiency as an individual-pixel optimization but with fewer computation efforts. Computer simulations demonstrated that the zone-boundary optimization for a 6 microm period grating increases the efficiency by 7% and 14.5% for 0.6 microm and 1.65 microm writing-spot diameters, respectively. The diffraction efficiency of as much as 65%-90% for 4-10 microm zone periods was obtained experimentally with this method.     

Sampling of the diffraction field

When optical signals, like diffraction patterns, are processed by digital means the choice of sampling density and geometry is important during analog-to-digital conversion. Continuous band-limited signals can be sampled and recovered from their samples in accord with the Nyquist sampling criteria. The specific form of the convolution kernel that describes the Fresnel diffraction allows another, alternative, full-reconstruction procedure of an object from the samples of its diffraction pattern when the object is space limited. This alternative procedure is applicable and yields full reconstruction even when the diffraction pattern is undersampled and the Nyquist criteria are severely violated. Application of the new procedure to practical diffraction-related phenomena, like in-line holography, improves the processing efficiency without creating any associated artifacts on the reconstructed-object pattern.     

Effect of surface plasmon excitations on the irradiance pattern of the return beam in optical disk data storage

The excitation of surface plasmons at a dielectric-metal interface is responsible for dips in the zeroth order diffraction efficiency of a metal grating at certain angles of incidence. The dips appear as dark bands in the returning irradiance pattern in an optical disk system and are seen only when there is a component of incident polarization that lies perpendicular to the tracks. The location of these bands is derived from theoretical considerations and is shown to depend on the track pitch and the materials involved, but not on the groove depth or width. The band locations are confirmed by zeroth order diffraction efficiency measurements as a function of incident angle. A possible negative effect of these bands on an optical disk system is the introduction of additional fluctuations and noise into the focusing and push-pull tracking signals.