自准直测量系统中离焦误差分析及修正

在自准直角度测量系统中,当光电接收装置即四象限探测器偏离透镜焦平面时,会在测量系统中引入离焦误差。为提升自准直测量系统的精度,该文利用实验室已有的自准直角度测量系统,将反射镜角度对处于离焦状态的测量系统产生的影响进行分析,利用雷尼绍激光干涉测量系统测得角度值作为标准量,与测量实验系统测得角度量进行对比,根据测量结果求出离焦距离。从实验结果可以看出,将离焦距离求出并对四象限探测器与透镜间间距进行调整后,自准直角度测量曲线重合,证明将离焦误差有效消除。     

使用位敏探测器PSD的焦面检测方法

本文介绍一种新的焦面检测方法,以位置敏感探测器PSD作为检焦器件对光学系统的实际焦面进行检测。该方法原理简单、处理快速方便、检测精度较高,特别适用于对透镜截距的测量和胶片摄影系统的精密调焦。还讨论了使用PSD测量先学系统其它参数的方法以及影响PSD测量精度的主要因素。文中还将PSD与CCD等器件做了一些比较,充分肯定了PSD驱动电路简单、处理速度快和分辨率高等优点。     

光谱共焦位移传感器物镜设计

高精度非接触式位移传感器有着广泛的应用.本文讨论其中一种采用光学方法实现非接触测量的光谱共焦位移传感器,阐述该传感器的工作原理,给出了该系统的设计方法和评价方法.最后基于光学设计软件CODE V的宏语言和数学软件MATLAB设计出了一个测量范围为0～1.173 mm的光谱共焦位移传感器物镜.该物镜采用一个单透镜和双胶合透镜组合的结构,在工作波长范围内,各个单波长对应最大的RMS半径为2.8 μm,其测量精度优于5 μm,波长离焦量和波长之间线性度通过线性回归拟合得出判定系数为0.985 9,测量的线性度优异.     

共轴两焦面探测信号的激光粒度测试

为了提高激光粒度仪测量宽分布范围粒径的能力,根据衍射原理,提出扩大测试动态范围的方法.该方法使用共轴的双透镜,在两个焦平面同时探测信号,将这些信号合成后经数据处理得到粒子尺寸分布.模拟计算表明,使用两个100mm焦距的透镜和两个32环的多元探测器可测量粒径为l～2000 μm的颗粒,动态范围为2000∶1.这种方法在不需更换镜头、不改变探测器轴向位置的情况下可以测量较大量程内的粒径分布.     

基于白光LED的光谱共焦位移传感器

为实现光谱共焦位移传感器的小型化、低功耗和高精度,在设计过程中选择体积小、耗电量小的白光LED作为传感器的光源,并使用光纤耦合器代替复杂的分光棱镜式光学系统结构。色散镜头采用消色差透镜与非球面透镜组合的方式,在使用较少透镜数量的情况下达到较好的像差校正能力。同时结合光强归一化等数据处理方法,消除白光LED光源光谱光强分布不均匀等因素对测量精度造成的影响,得到准确、稳定的峰值波长与位置间的对应关系。通过双频激光干涉仪对系统进行标定和测量,实验结果表明使用435~655 nm波段,系统测量范围可以达1.7 mm,平均测量精度1.8μm,满足一定的测量需求。     

衍射微透镜在红外单元探测器中的应用

研究了衍射微透镜提高红外探测器探测能力的方法,通过实验将衍射微透镜耦合到红外单元探测器上,使语组合件的响应度提高到３．２倍、比探测率提高到４．２倍。结果表明：采用微透镜作光聚能器后,探测器光敏面面积可减少而光能利用率增加,探测性能提高。衍射微秀镜的结构小,有利于与探测器集成,其研究极具实用价值。     

热电型光辐射探测器时间响应特性的研究

介绍了常用的腔型和平面型两种热电型光辐射探测器时间响应特性的测量方法和测量结果.测量结果表明不论是腔型还是平面型光辐射探测器,其时间响应特性都不是理论预言的简单指数衰减函数,而是包含两个指数衰减函数的组合函数;探测器达到平衡的时间是入射光功率的函数,两种探测器的平衡时间都可能很长.所以,如何选取测量读数前等待平衡时间对测量结果有重要影响.对该项因素的影响进行了分析,并提出了解决办法.     

用于毫米波焦面阵成像系统的扩展半球介质透镜

毫米波成像是近年来毫米波领域的一个研究热点,而焦面阵成像因其具有实时成像的优点更加受到重视。中分析可用为面阵成像的扩展半球介质透镜。这种焦面阵成像结构将集成天线阵贴附在透镜背面接收透镜聚焦的功率,消除了集成天线工作在毫米波频段时存在的表面波对天线性的影响,具有尺寸紧凑、损耗小的特点。采用Stratton-Chu公式和射线追迹分析了电磁波入射到扩展半球透镜上时在其背面的场分布,即透镜的焦区场分布,以获得透镜用于焦面阵成像时的性能。为验证分析方法的正确性,对平面波垂直入射和会聚高斯束入射两种情形进行了实验验证,实验结果与理论分析吻合较好。该透镜天线还可用来消除常规集成毫米波系统中抛物面天线与集成前端之间的过渡,以降低损耗,改善系统性能,也可用于与准光系统的连接或耦合。该结果将对上述应用提供理论指导。     

哈特曼法焦度测量模型的误差分析及修正

为了减少屈光度测量误差,提高精度。本文针对哈特曼法焦度测量建立了较详细的误差模型,着重分析了光源的色散误差、入射光与透镜未垂直、光电探测器中心定位不准、透镜倾斜、光源光线主轴与透镜主轴未重合所引起的屈光度测量误差。结果表明,得出由于光电探测器上中心提取的不准确,会对最终的结果产生较大的误差。并由此提出了双重双线性插值结合拟合法来求取中心的方法,并证明了其有效性和准确性。     

带分划板的连续变倍双筒望远镜设计

介绍一种用两组元透镜来实现倒象和连续变倍的双筒望远镜设计。该设计在物镜焦面位置安装带刻线的分划板 ,可对目标进行瞄准和测量。特别是在系统不另设可变光栏的情况下 ,利用光学系统透镜边框作孔径光栏 ,使系统在整个变倍过程中不仅出瞳直径和出瞳距离均变化不大 ,而且系统与定倍望远镜一样具有较大的象方视场、出瞳直径和出瞳距离 ,从而使系统无论昼夜使用都具有真正的变倍作用和良好的观察效果。     

Alternative method for measuring effective focal length of lenses using the front and back surface reflections from a reference plate

We present a simple method for measuring the effective focal length without determining the location of principle plane of the lens. The method is based on the measurement of confocal backreflection axial responses from the front and back surfaces of a reference plate with known refractive index and thickness. We proved the concept by measuring the effective focal lengths of thin singlet lenses and complex microscope objectives. The theoretical limit of measurement precision varies depending on the numerical aperture of the lens. This method can provide an alternative focal length measurement method for complex lenses or lenses that are permanently attached to other structures. Measurement errors were analyzed theoretically and improvements in measurement accuracy were discussed.     

Use of confocal microscopes in conoscopy and ellipsometry. 1. Electromagnetic theory

An optical system consisting of two objective lenses in a confocal arrangement is examined. It is shown that a simple algebraic relation exists between the electric field in the back focal plane of the first objective lens, which focuses the incident light, and the Fourier transform of the electric field in the focal plane of the same lens. The relation holds for high angles. If a thin object is placed in the focal plane it is possible to write the electric field by use of a Fourier transform relation at the exit aperture of the second lens. The theory is generalized for objects that are positioned at oblique angles with respect to the optical axis of the system. This configuration is clearly identical to the setup of a spatially resolving ellipsometer.     

Focal plane position detection with a diffractive optic for shack-hartmann wave-front sensor fabrication

During construction of a Shack-Hartmann wave-front sensor it is critical that the spacing between the lens array and the detector array be equal to the lens array focal length to obtain accurate and precise measurements of a wave front. This separation is often difficult to determine with large f/# lenses, because their focal spot diameter does not change substantially for small displacements on either side of the focal plane. We describe a method with an array of off-axis lens segments for determining the location of the focal plane. Because the lenses are off axis, changes in the distance from the optic to the detector array result in transverse focal spot position variations as a function of their separation from the lenses. By analyzing the focal spot pattern on a CCD, we achieved 12-mum rms error in the axial position measurement while moving a 4-mm-focal-length optic over 1 mm.     

Self-pumped phase-conjugate interferometer with a photorefractive iron-doped lithium-niobate crystal

A single object wave is amplitude divided by a beam splitter into two waves of equal intensity that are made to interfere at the back surface of an iron-doped lithium-niobate crystal so that the normal to the back surface is the angular bisector of the input waves. The interference results in the formation of a phase grating (Bragg grating) in the volume of the crystal. These waves are diffracted at the Bragg grating on both the front focal plane and the back focal plane of the crystal. The wave diffracted in the back focal plane from the Bragg grating and counterpropagating to the incident wave is observed to be the phase conjugate of the input object wave. The wave diffracted in the front focal plane of the Bragg grating is incorporated into the design of an interferometer to measure a specific in-plane displacement of the object wave. It is theoretically evaluated and experimentally demonstrated that interferometers such as those that incorporate conjugate-wave pairs are highly sensitive.     

Simple focal-length measurement technique with a circular Dammann grating

A novel technique for focal-length measurements with a circular Dammann grating is presented. In the back focal plane of the lens under test, a one-order circular Dammann grating with limited aperture will produce double-humped radial rings. The separation between the two lobes varies with the displacement of the observed plane from the focal plane of the lens. By searching for the position at which the separation is minimal, the focal point of the lens can be located and hence the back focal length can be determined. Experimental results demonstrated that this method is efficient and can be used effectively for a quick check of focal length.     

Anamorphic white light Fourier processor with holographic lenses

Two anamorphic and achromatic Fourier processors were designed and constructed using diffractive and refractive cylindrical lenses. The diffractive lenses are holographic lenses recorded on silver halide material. In both processors the achromatic one-dimensional Fourier transform plane was obtained with two holographic lenses and one refractive cylindrical lens. The image with the same magnification in both directions at the output plane was formed with two different combinations of lenses. The differences between the two processors are analyzed, and in both cases the chromatic aberration in the Fourier plane and in the output plane is evaluated. Even though single cylindrical refractive lenses were used to image in one direction, good results were obtained.     

Redesign and improved performance of the tropospheric ozone lidar at the Jet Propulsion Laboratory Table Mountain Facility

Improvements to the tropospheric ozone lidar at the Jet Propulsion Laboratory Table Mountain Facility for measurements of ozone profiles in the troposphere and lower stratosphere, between approximately 5-and 20-km altitude, are described. The changes were primarily related to the receiver optical subsystems and the data-acquisition system. The original 40-cm Cassegrain telescope was replaced with a faster (f/3) 91-cm Newtonian mirror. In the focal plane of this mirror, the lidar signal is divided into two parts by use of two separate optical fibers as field stops corresponding to different but neighboring 0.6-mrad fields of view. We then separate the two received wavelengths by aligning each transmitted beam to one of the fibers. In addition, two 50-mm telescopes are used for the collection of near-range returns. The four optical signals are brought to a chopper wheel for independent signal selection in the time and range domain. For each channel, an interference filter is used for skylight rejection and additional cross-talk prevention. The signals are detected with miniature photomultiplier tubes and input to a fast photon-counting system. The goals of these modifications were to increase the spatial and temporal resolution of the lidar, to extend the altitude range covered, to improve the quality of the raw data, and to enable regular and routine operation of the system for long-term measurements.     

Measurement of parameters of simple lenses using digital holographic interferometry and a synthetic reference wave

The use of digital holographic intrerferometry in the testing of simple thin lenses is explored. Focal length, radius of curvature, and refractive index are the lens parameters that can be determined using this method. The digital holograms using the lens under test are recorded at various positions of the test lens using off-axis geometry. This is combined with a digitally computed plane wavefront to determine the curvature of the light beam emerging from the test lens. Focal length is the position of the test lens where a single fringe results. The radius of curvature of the test lens is also determined similarly using a long focal length lens to concentrate a collimated beam onto the test lens. The nonuniformities on the lens surface could also be found by using this method. The implementation of the method is shown by using computer simulations in the case of biconvex lenses. The method can be utilized to measure the parameters of plano-convex and concave lenses also.     

The Design of Optical Systems with Extended Depth of Focus

The SLAMS Version 14 optimization programme was modified to include geometrical MTF values, in two defocused image planes, in the merit function. This programme was successfully used in the design of lenses for office copying machines. In such cases, a major effort is made to extend the focal depth maintaining a given MTF value. Conventional methods which minimize the aberrations in a single image plane may be less adequate under those circumstances.     

Approach to 3-d ultrasound high resolution imaging for mechanically moving large-aperture transducer based upon Fourier transform

A new three-dimensional (3-D) acoustic image formation technique is proposed that is based on the transmission of wide bandwidth pulse signals and the application of the 3-D fast Fourier transform. A solution to the Helmholtz wave equation has been obtained using the Born approximation. The solution contains analytical expressions for the spatial spectra of the transmit and receive radiation patterns for transducers of various geometries with lenses of fixed focal distances. It has been shown that the proposed algorithms allow for radiation patterns with constant widths at depths both behind and in front of the focal point, starting practically from the plane of the transducer. The theoretical and experimental investigations and computer simulation for both spherical and rectangular transducer shapes have been performed. The results were used to estimate the beamwidths and the side lobe levels. A variant of the linear array has been studied for a cylindrical lens of a fixed focal distance moving in a lateral direction. It has been shown that, in this case, a high resolution (of the order of a few wavelengths) can be achieved along all three Cartesian coordinates at a very high scanning velocity. The influence of the moving scatterers' velocity in inhomogeneous medium on the spatial radiation pattern characteristics has been estimated.