数字无透镜傅里叶变换全息术中非傍轴及离焦像差的校正

对数字无透镜傅里叶变换全息图直接采用逆傅里叶变换进行物场的数值重建时.需要满足两个条件:第一,全息图的记录过程必须满足傍轴近似条件,否则再现过程中会产生非傍轴像差;第二,记录全息图时物平面与参考点光源到全息图记录平面的距离必须相等,否则再现过程中会产生离焦像差.理论分析了非傍轴及离焦记录条件下数字无透镜傅里叶变换全息图的灰度分布特点,并提出了相应的非傍轴及离焦像差的数值校正方法.根据实际的非傍轴或离焦记录情况.分别给所记录的数字全息图灰度分布矩阵乘以适当的非傍轴或离焦校正因子,以消除灰度矩阵中非傍轴或离焦因素的影响.然后再对校正后的伞息图灰度矩阵做逆傅里叶变换处理.即可得到准确的数字再现像.实验结果表明.该数值重建方法能够有效地消除无透镜傅里叶变换全息术中数字再现像的非傍轴像差及离焦像差,提高再现像的质量.     

用改进的两步模拟退火法进行二元光学元件的设计

为了减少二元光学元件设计的计算量并提高设计精度,在对现有算法机理进行深入分析的基础上,提出了适用于二元光学元件设计的两步模拟退火法.该算法在整个退火过程中采用先量化后优化的策略,并将优化过程分为两个阶段：搜索并锁定最优解区间;快速收敛到最优解.模拟实验显示,与传统设计方法相比,该算法不仅保持了全局寻优的特点,而且提高了稳健性和效率.算法剔除了对设计结果影响较大的量化误差,提高了设计精度.用此法实例设计了单焦面辐射聚焦元件,得到了与目标图像一致的光学实验结果.     

基于基元全息图空间频谱分析的计算全息参考光角度选择方法

提出了一种基于基元全息图频谱分析的计算全息参考光角度选择方法.通过分析基元全息图的空间频谱成分,导出全息图正确再现需要满足的约束条件;求解了基于空间光调制器的计算全息再现系统的参考光角度取值范围;用N-LUT算法计算了成像距离为1 000mm时,一幅22.5mm×26.1mm的二维图像取不同参考光角度时的全息图,并进行了数字再现和光学再现实验.结果表明:参考光角度在0.893 8°到1.398 0°之间选择可以获得质量良好的再现像;参考光角度小于0.893 8°时,再现像与共轭像不能完全分离,参考光角度大于1.398 0°时,全息图频率过高会造成欠采样,导致再现像与下一级共轭像互相交叠.实验现象与理论分析一致,验证了参考光夹角选择方法的正确性.     

Multi-location laser ignition using a spatial light modulator towards improving automotive gasoline engine performance

We report on a study into multi-location laser ignition (LI) with a Spatial Light Modulator (SLM), to improve the performance of a single cylinder automotive gasoline engine. Three questions are addressed: i/ How to deliver a multi-beam diffracted pattern into an engine cylinder, through a small opening, while avoiding clipping? ii/ How much incident energy can a SLM handle (optical damage threshold) and how many simultaneous beam foci could thus be created? ; iii/ Would the multi-location sparks created be sufficiently intense and stable to ignite an engine and, if so, what would be their effect on engine performance compared to single-location LI? Answers to these questions were determined as follows. Multi-beam diffracted patterns were created by applying computer generated holograms (CGHs) to the SLM. An optical system for the SLM was developed via modelling in ZEMAX, to cleanly deliver the multi-beam patterns into the combustion chamber without clipping. Optical damage experiments were carried out on Liquid Crystal on Silicon (LCoS) samples provided by the SLM manufacturer and the maximum safe pulse energy to avoid SLM damage found to be 60 mJ. Working within this limit, analysis of the multi-location laser induced sparks showed that diffracting into three identical beams gave slightly insufficient energy to guarantee 100% sparking, so subsequent engine experiments used 2 equal energy beams laterally spaced by 4 mm. The results showed that dual-location LI gave more stable combustion and higher engine power output than single-location LI, for increasingly lean air-fuel mixtures. The paper concludes by a discussion of how these results may be exploited.     

分数傅里叶变换全息图及其在防伪中的应用

提出分数傅里叶变换全息图,讨论了它的性质。拍摄分数傅里叶变换彩虹全息图。基于其再现条件的特殊性,可建立一种新型的伪全息术。     

光折变多重存储的栅自增强读出特性研究

研究了光折变重存储读出时折射率栅自增强特性与记录晶体厚度、记录时的光强比以及写入的折射率栅振幅之间的关系.结果表明记录晶体的厚度大于某一值,才有自增强效应;较小的参物光强比具有较大的自增强效果,能获得较大的读出衍射效率;自增强读出所能达到的最大衍射效率与写入的栅振幅大小无关,而读出时衍射效率增加的速率与写入的栅振幅成反比.     

拍摄白光再现全息图的一种方法

本文给出了一种拍摄白光再现全息图装置 ,所拍的全息图在阳光或白炽灯照明下清晰地再现被拍的物体形象     

Effect of UV radiation on the diffraction efficiency of holograms when recording in additively colored KCl crystals

We have shown that the increase in diffraction efficiency of holograms recorded in additively colored crystals as a result of preliminary UV irradiation may be due not only to an increase in the concentration of F centers but also to radiolysis of impurity hydroxyl ions, which are always present in nominally pure crystals. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 85–87, January–February, 2008.     

纯位相信息自聚焦计算全息匹配滤波器

本文介绍一种用计算全息方法制作的纯位相信息自聚焦匹配滤波器。它在编码时取滤波函数的振幅为１,仅对位相进行编码;并通过对傅里叶谱加入二次位相因子代替傅里叶透镜,使其具有自聚焦功能。与常规的方法（光学全息法或计算全息法）所获得的匹配滤波器相比较,具有原理上更合理,滤波器的制作和匹配光路更简单,也更容易实现匹配等特点。所得到的匹配实验结果也很清晰,这与理论是完全符合的。