Hybrid wavefront sensor for the fast detection of wavefront disturbances

Strongly aberrated wavefronts lead to inaccuracies and nonlinearities in holography-based modal wavefront sensing (HMWS). In this contribution, a low-resolution Shack-Hartmann sensor (LRSHS) is incorporated into HMWS via a compact holographic design to extend the dynamic range of HMWS. A static binary-phase computer-generated hologram is employed to generate the desired patterns for Shack-Hartmann sensing and HMWS. The low-order aberration modes dominating the wavefront error are first sensed with the LRSHS and corrected by the wavefront modulator. The system then switches to HMWS to obtain better sensor sensitivity and accuracy. Simulated as well as experimental results are shown for validating the proposed method.     

Detection of phase singularities with a Shack-Hartmann wavefront sensor

While adaptive optical systems are able to remove moderate wavefront distortions in scintillated optical beams, phase singularities that appear in strongly scintillated beams can severely degrade the performance of such an adaptive optical system. Therefore the detection of these phase singularities is an important aspect of strong-scintillation adaptive optics. We investigate the detection of phase singularities with the aid of a Shack-Hartmann wavefront sensor and show that, in spite of some systematic deficiencies inherent to the Shack-Hartmann wavefront sensor, it can be used for the reliable detection of phase singularities, irrespective of their morphologies. We provide full analytical results, together with numerical simulations of the detection process.     

High-speed Shack-Hartmann wavefront sensor design with commercial off-the-shelf optics

Several trade-offs relevant to the design of a two-dimensional high-speed Shack-Hartmann wavefront sensor are presented. Also outlined are some simple preliminary experiments that can be used to establish critical design specifications not already known. These specifications include angular uncertainty, maximum measurable wavefront tilt, and spatial resolution. A generic design procedure is then introduced to enable the adaptation of a limited selection of CCD cameras and lenslet arrays to the desired design specifications by use of commercial off-the-shelf optics. Although initially developed to aid in the design of high-speed (i.e., megahertz-frame-rate) Shack-Hartmann wavefront sensors, our method also works when used for slower CCD cameras. A design example of our procedure is provided.     

小波滤波在Shack-Hartmann传感器上的应用

在使用Shack-Hartmann传感器进行大口径非球面镜面检测中,外部环境的各种振动影响以及气流、温差的干扰都会使检测精度下降。针对这个问题,提出了一种新的时域小波滤波技术。这项技术可以对传感器的信号干扰在时间域上进行不同层次的小波分析,提取干扰信号的先验特征,对测量数据进行有效的滤波,减小波前的扰动起伏,以更准确地探测质心。实验结果表明,采用这种技术后,Shack-Hartmann波前传感器对光学镜面检测的静态测量精度提高了50%以上,离散性减少到原来的20%-30%。     

Efficient implementation of a spatial light modulator as a diffractive optical microlens array in a digital Shack-Hartmann wavefront sensor

A traditional Shack-Hartmann wavefront sensor (SHWS) uses a physical microlens array to sample the incoming wavefront into a number of segments and to measure the phase profile over the cross section of a given light beam. We customized a digital SHWS by encoding a spatial light modulator (SLM) with a diffractive optical lens (DOL) pattern to function as a diffractive optical microlens array. This SHWS can offer great flexibility for various applications. Through fast-Fourier-transform (FFT) analysis and experimental investigation, we studied three sampling methods to generate the digitized DOL pattern, and we compared the results. By analyzing the diffraction efficiency of the DOL and the microstructure of the SLM, we proposed three important strategies for the proper implementation of DOLs and DOL arrays with a SLM. Experiments demonstrated that these design rules were necessary and sufficient for generating an efficient DOL and DOL array with a SLM.     

Improving the performance of a pyramid wavefront sensor with modal sensitivity compensation

We describe a solution to increase the performance of a pyramid wavefront sensor (P-WFS) under bad seeing conditions. We show that most of the issues involve a reduced sensitivity that depends on the magnitude of the high frequency atmospheric distortions. We demonstrate in end-to-end closed loop adaptive optics simulations that with a modal sensitivity compensation method a high-order system with a nonmodulated P-WFS is robust in conditions with the Fried parameter r 0 at 0.5 microm in the range of 0.05-0.10 m. We also show that the method makes it possible to use a modal predictive control system to reach a total performance improvement of 0.06-0.45 in Strehl ratio at 1.6 microm. Especially at r 0=0.05 m the gain is dramatic.     

Response analysis of holography-based modal wavefront sensor

The crosstalk problem of holography-based modal wavefront sensing (HMWS) becomes more severe with increasing aberration. In this paper, crosstalk effects on the sensor response are analyzed statistically for typical aberrations due to atmospheric turbulence. For specific turbulence strength, we optimized the sensor by adjusting the detector radius and the encoded phase bias for each Zernike mode. Calibrated response curves of low-order Zernike modes were further utilized to improve the sensor accuracy. The simulation results validated our strategy. The number of iterations for obtaining a residual RMS wavefront error of 0.1λ is reduced from 18 to 3.     

Integration of a photodiode array and centroid processing on a single CMOS chip for a real-time shack-Hartmann wavefront sensor

A real-time VLSI optical centroid processor has been developed as part of a larger Shack-Hartmann wavefront sensor system for applications in adaptive optics. The implementation of the optical centroid detection system was demonstrated successfully using a hardware emulation system. Subsequently, the design has been implemented as a CMOS single-chip solution. This has advantages in terms of speed, power consumption, system size, and cost. The design of the different components of the system will be discussed along with test results of the fabricated device.     

对Hartmann-Shack波前传感器平移误差的研究

Hartmann—Shack传感器的探测精度对于评价自适应光学系统的校正能力和光学检测精度都是十分重要的。通过对传感器的平移误差的理论分析和数据仿真来对传感器的系统精度进行研究，确定平移误差的最佳范围为残余像差与理论像差的均方根比值不大于0．5％。这为Hartmann—Shack传感器的装配提供了理论依据和技术指标。     

Accurate and precise optical testing with a differential Hartmann wavefront sensor

A novel differential Hartmann sensor is described. It can be used to determine the characteristics of an optic accurately, precisely, and simply without detailed knowledge of the wavefront used to illuminate the optical system or of the geometry of the measurement system. We demonstrate the application of this sensor to both zonal and modal optical testing of lenses. We also describe a dual-camera implementation of the sensor that would enable high-speed optical testing.     

曲率波前传感器波前重构算法的研究

运用衍射理论计算出两个离焦面上的光强分布,从而获得波前曲率和孔径边缘的波前径向倾斜。根据Zernike多项式的微分特性,采用两种不同的方法分别处理曲率和倾斜,使用积分的方法解决了在边界上δ函数很难处理的问题。由探测器的几何分布预先算出控制矩阵,用Zernike多项式曲线拟合的方法重构出波前。计算机仿真表明,波前残差小于5％,验证了此波前重构算法的可行性。     

Calibration and performance of a pyramid wavefront sensor for the eye

We describe the calibration and performance of a pyramid wavefront sensor designed for use in a retinal imaging camera. The effect of the image modulation and the sensor binning on the measurements are explained in detail and various tests to validate the performance are described. The wavefront sensor was incorporated into an adaptive optics system that used a magnetically actuated deformable mirror, and results on static test optics are shown.     

The VXI electronics of the DIAMANT particle detector array

A VXI card designed for the processing of signals from the particle detector array DIAMANT, a CsI(Tl) light charged particle ancillary detector system to the EUROBALL and the EXOGAM gamma-spectrometers, is described. The card provides particle energy, particle-type and time-reference information and is compatible with the existing signal-processing system of EUROBALL/EXOGAM. In order to have full compatibility with the electronics of these spectrometers without sacrificing the performance of the card, some new solutions are used in the signal processing. For particle discrimination three methods can be selected; the ballistic deficit method, the zero-crossing method and a combination of these two methods. The figure of merit of the particle discrimination using the combined method is better than that of the zero crossing or the ballistic deficit method individually. Timing signals for particle–gamma coincidence are derived by a specially designed non-delay-line constant fraction discriminator, which exhibits low rise-time-dependent walk. The card has been tested with EUROBALL. The results of these tests are presented.     

双光束光电二极管阵列检测器的设计

由于普通光电二极管阵列检测器无法克服光源波动造成的影响,故设计开发了一种双光束光电二极管阵列检测器。该检测器采用光导纤维束将光源发出的光分成两束,在斩光器的调制下分时射入样品吸收池和参比吸收池。透射出的光信号通过光导纤维束射到狭缝上,被凹面光栅分光成像于光电二极管阵列上。在斩光器和后续电路的配合下,实现了在同一个光电二极管阵列上信号光光谱、参考光光谱和暗电流的分时测量。由于采用参考光光谱和光电二极管阵列暗电流对信号光谱进行实时补偿,可以使基线短期噪声降低为1×10-5AU,漂移降低为1×10-4AU/h。     

基于哈特曼传感器的激光波前分布测量技术

激光波前分布作为ISO新列入的衡量激光光束质量的重要参数,对其有效、准确地测量显得十分重要.根据哈特曼波前测量原理,详细介绍了基于哈特曼传感器的激光波前分布测量装置、哈特曼传感器波前斜率测量方法和常用波前重构算法,引入一种定标哈特曼传感器针孔阵列与CCD间距的方法,分析定标实验数据及使用已定标的哈特曼波前分析仪测量波前的实验结果.实验证明定标方法可靠有效.     

Binocular open-view Shack-Hartmann wavefront sensor with consecutive measurements of near triad and spherical aberration

We have developed a binocular open-view Shack-Hartmann wavefront sensor for measuring time variation of binocular accommodation, vergence, pupil sizes (i.e., the binocular near triad), and monochromatic aberrations. The device measures these values16 times per second for up to 1 min. Our purpose is to introduce the new instrument. We have confirmed the accuracy of the device. Refractions for a 4 mm pupil were accurate across the range of measurements of model eyes and normal human eyes. We measured binocular dynamics of accommodation, vergence, and spherical aberrations.     

大视场阵列探测器归心算法研究

为了实现空间光通信系统小型化、一体化设计,建立了基于阵列探测器和快速偏转镜的一体化跟踪系统,通过分析阵列探测器的光斑位置检测原理提出了一种归心算法。首先通过设置阈值,设计了光斑不完全覆盖探测器的粗归心策略;然后采用数据库查询的方法完成精归心,最后采用无穷积分法使光斑归至原点附近;通过搭建试验平台验证了算法的正确性和可行性。实验结果表明：跟踪视场可达70.3 mrad,较原算法视场扩大了约3倍,跟踪最大误差优于1.8 μrad,为空间光通信系统的进一步工程化应用奠定了基础。     

Adaptive K-NN for the detection of air pollutants with a sensor array

The field of air-quality monitoring is gaining increasing interest, with regard to both indoor environment and air-pollution control in open space. This work introduces a pattern recognition technique based on adaptive K-nn applied to a multisensor system, optimized for the recognition of some relevant tracers for air pollution in outdoor environment, namely benzene, toluene, and xylene (BTX), NO/sub 2/, and CO. The pattern-recognition technique employed aims at recognizing the target gases within an air sample of unknown composition and at estimating their concentrations. It is based on PCA and K-nn classification with an adaptive vote technique based on the gas concentrations of the training samples associated to the K-neighbors. The system is tested in a controlled environment composed of synthetic air with a fixed humidity rate (30%) at concentrations in the ppm range for BTX and NO/sub 2/, in the range of 10 ppm for CO. The pattern recognition technique is experimented on a knowledge base composed of a limited number of samples (130), with the adoption of a leave-one-out procedure in order to estimate the classification probability. In these conditions, the system demonstrates the capability to recognize the presence of the target gases in controlled conditions with a high hit-rate. Moreover, the concentrations of the individual components of the test samples are successfully estimated for BTX and NO/sub 2/ in more than 80% of the considered cases, while a lower hit-rate (69%) is reached for CO.     

Si基微绝热结构PLZT厚膜红外探测器阵列

介绍了一种制备非致冷红外探测器阵列的新方法,此方法避免了使用传统的微电子机械系统(MEMS)工艺来加工微桥.研究了如何在Si基片表面形成ZnO膜层网格状结构的方法.ZnO纳米粉末和PLZT厚膜采用改进的溶胶-凝胶法制备.表征了ZnO纳米粉末的表面形貌和PLZT厚膜的相组成,测量了 PLZT-8/53/47厚膜的铁电性和热释电性.结果表明,ZnO纳米粉末的粒径为40～70 nm,PLZT-8/53/47厚膜为纯钙钛矿相,其主结晶方向与底电极一致.PLZT-8/53/47厚膜具有优良的热释电性能,其热释电系数p为8.21×10-8C/(cm2·℃),而矫顽场较小,25℃时 Ec为32.0 kV/cm,40℃时 Ec仅为27.8 kV/cm.