A position sensor based on grating projection with spatial filtering and polarization modulation

A position sensor based on grating projection with spatial filtering and polarization modulation is presented. A grating is projected onto the object to be measured through a 4f optical system with a spatial filter. After reflected by the object, the grating projection is imaged on a detection grating through another 4f optical system to form moire fringes. The polarization modulated moire signal is detected to obtain the position information of the object. In the position sensor, the moire signal varies sinusoidally with the position of object. The measurement is independent of the incident intensity on the projection grating and the reflectivity of the object to be measured. In experiments, the effectiveness of the position sensor is proved, and the root mean square (RMS) error at each measurement position is less than 13 nm.     

A novel polarization modulator for a moiré system with grating imaging

Displacement measurements and position sensing have been playing an important role in many fields such as fabrication, biophysics, and autocontrol. Interferome- try, laser triangulation, optical fiber sensing and moiré technique are common optical measuring methods[1-3]. Among these methods, moiré technique holds the most interest due to its high accuracy, large range, low cost, and other advantages. When a long working distance is required, or when space is not at a premium, a moiré sys- t…     

光刻机照明光场均匀性高精度校正方法研究

提出了应用于光刻机照明系统照明光场均匀性的高精度校正方法,该方法通过优化手指阵列式均匀性校正器中校正手指前端的形状及其排布方式来提高校正能力和精度。仿真结果表明:当校正手指错开排布时,手指阵列式均匀性校正器的校正精度优于0.2%;当校正手指的前端有倒斜角且双层错开排布时,手指阵列式均匀性校正器的校正精度优于0.16%,比常规手指阵列式均匀性校正器的校正精度提高约一倍。     

自动对靶喷雾靶标红外探测研究

农林作物一般非连续种植,喷在农林作物靶标之间的药液造成巨大浪费和严重环境污染,因此探讨利用红外线探测技术实现靶标的自动探测, 对靶精准喷施意义重大。红外线可有效防止可见光的干扰,响应速度快,可实现无接触探测,由此建立的红外光电探测系统可靠性好、成本低。红外发光管发射出红外光照射到被探测物体上,反射的红外线被光电探测器接收,触发控制信号,实现自动对靶施药。系统中不同探测器组采用不同编码的调制脉冲红外信号,可消除组间光路干扰及其他光信号的干扰。实验结果表明所建立的红外靶标自动探测装置可对农林作物靶标进行自动探测,光波波长为850 nm,探测距离为0.1～6 m可调,靶标最小识别间距小于0.3 m。     

Sinusoidal phase-modulating laser diode interferometer for real-time surface profile measurement

A sinusoidal phase-modulating (SPM) laser diode (LD) interferometer for real-time surface profile measurement is proposed and its principle is analyzed. The phase signal of the surface profile is detected from the sinusoidal phase-modulating interference signal using a real-time phase detection circuit. For 60 x 60 measurement points of the surface profile, the measuring time is 10 ms. A root mean square (RMS) measurement repeatability of 3.93 nm is realized, and the measurement resolution reaches 0.19 nm.     

Real-time measurement of retardation of eighth-wave plate independent of fast-axis direction

A real-time measurement method for the retardation of an eighth-wave plate is proposed. The collimated laser beam is split using a Glan Taylor polarizer with two side escape windows. The reflected sub-beam is detected using a detector, whereas the transmitted sub-beam passes through the quarter-wave plate and the eighth-wave plate of interest. Then, it is reflected by the mirror and passes reversely through the eighth-and quarter-wave plates. Finally, it is analyzed using the Glan Taylor polarizer and detected using another detector. With two detection signals, the retardation is resolved and found to be independent of the fast-axis direction, initial intensity, and circuit parameters. In the experiment, a crystal quartz sample is measured at different fast-axis angles. The standard deviation of the retardation is 0.9 o . The usefulness of the method is verified.     

基于支持向量机的玉米苗期田间杂草光谱识别

田间全面积均匀喷施除草剂不经济,还污染环境,精准喷施除草剂意义重大,其关键是正确识别杂草。用便携式野外光谱仪,在田间测量了玉米、马唐和稗草植株冠层在350～2 500 nm波长范围内的光谱数据,经过数据预处理,数据分析波长选为350～1 300和1 400～1 800 nm。数据处理采用支持向量机(SVM)模式识别方法。SVM具有可实现对小样本建模结构风险最小化、结果最优化、泛化能力强的优点。用线性、多项式、径向基和多层感知核函数对玉米和杂草建立二分类模型,结果表明,三阶多项式核函数SVM分类模型的正确识别率最高,达到80%以上,且支持向量比例较小。以二分类模型为基础,利用投票机制,建立了玉米、马唐和稗草的一对一多分类SVM模型,正确识别率达80%。田间光谱测量受光照、背景和仪器测量精度等条件的影响较大,但结果仍表明SVM结合光谱技术在田间杂草识别中应用潜力很大,此研究为田间杂草识别及传感器的建立提供了一种研究思路和应用基础。     

Imaging method of single layer graphene on metal substrate based on imaging ellipsometer with large field of view

Single layer lattice graphene deposited on the metal substrate can hardly be imaged by the optical microscope. In this Letter, a large field-of-view imaging ellipsometer is introduced to image single layer graphene which is deposited on a metal substrate. By adjusting the polarizer and the analyzer of imaging ellipsometer, the light reflected from surfaces of either single layer graphene or a Au film substrate can be extinguished, respectively.Thus, single layer graphene can be imaged correspondingly under brightfield or darkfield imaging modes. The method can be applied to imaging large-area graphene on a metal substrate.     

Position sensor based on slit imaging

A position sensor based on slit imaging is proposed and its measurement principle is described. An imaging slit is illuminated by a collimated laser beam with square-wave modulation and imaged on a detection double slit through a 4f system. A magnified image of the detection double slit is formed on a bi-cell detector. The position of the imaging slit is obtained by detecting light intensity on two parts of the hi-cell detector. In experiments, the feasibility of the sensor was verified. The repeatability was less than 40 nm.