Performance evaluation of a sensorless adaptive optics multiphoton microscope

A wavefront sensorless adaptive optics technique was combined with a custom‐made multiphoton microscope to correct for specimen‐induced aberrations. A liquid‐crystal‐on‐silicon (LCoS) modulator was used to systematically generate Zernike modes during image recording. The performance of the instrument was evaluated in samples providing different nonlinear signals and the benefit of correcting higher order aberrations was always noticeable (in both contrast and resolution). The optimum aberration pattern was stable in time for the samples here involved. For a particular depth location within the sample, the wavefront to be precompensated was independent on the size of the imaged area (up to ～360 × 360 μm²). The mode combination optimizing the recorded image depended on the Zernike correction control sequence; however, the final images hardly differed. At deeper locations, a noticeable dominance of spherical aberration was found. The influence of other aberration terms was also compared to the effect of the spherical aberration.     

利用激光全息技术校正大口径光学成像系统像差

基于光学全息原理,分析了激光全息技术校正光学成像系统像差的机理和方法,建立了全息记录实验系统,用于校正口径500 mm、低质量球面反射镜光学系统对有限远物体成像时的像差。采用原光路再现的方法,通过比较像差校正前后的干涉图样和成像结果,验证了该校正方法的可行性。实验结果表明,校正后该系统剩余波像差约为λ/8。     

应用像差理论评估镜面热变形对成像的影响

通过多项式拟合法计算由于热变形导致的面形改变量,来修正镜面面形系数;然后应用平面对称光学系统的像差理论,计算它对成像的影响.和以往方法不同的是它通过像差形式解析表达,并能得到光线在像面上的点列图分布.如果热变形导致的镜面改变量分布比较复杂,很难用单个面形精确地拟合,建议进行分区拟合以减小拟合误差.最后,通过一个实例,用...     

模拟退火-爬山混合算法用于无波前传感器快速像差校正

为了校正激光光束波前像差,建立了一种基于压电微变形镜的自适应光学系统。提出了用模拟退火-爬山混合算法来控制系统中37单元单压电片变形镜,补偿激光光束波前像差,实现对光斑的快速校正。提出的混合算法先使用模拟退火算法为爬山法提供一个较好的校正起点,再用爬山法对像差进行精确校正,仅需要少量的模拟退火迭代过程即可提供一个好的校正起点。由于精确校正阶段的爬山法速度快,因此获得相同校正效果需要的迭代次数比普通模拟退火算法减少了50%以上;同时由于爬山法校正起点较好,大大降低了进入局部最优值的可能。最后,实验验证了模拟退火-爬山法对激光光束波前具有更佳的校正效率。     

制作平面全息光栅的离轴抛物镜/洛埃镜干涉系统

设计和制作具有较高波前平面度和结构稳定的干涉曝光系统是研制高质量平面全息光栅的首要条件.对离轴抛物镜/洛埃镜系统、单透镜/洛埃镜系统、球面反射镜/洛埃镜系统和双分离透镜/洛埃镜系统等4种单反射镜干涉曝光系统产生的干涉条纹直线度进行了光线追迹.在干涉场中放置标准光栅,使用于曝光的两束平行光入射到光栅上,从而衍射光相干叠加...     

Design of an aberration corrected low-voltage SEM

The low-voltage foil corrector is a novel type of foil aberration corrector that can correct for both the spherical and chromatic aberration simultaneously. In order to give a realistic example of the capabilities of this corrector, a design for a low-voltage scanning electron microscope with the low-voltage foil corrector is presented. A fully electrostatic column has been designed and characterised by using aberration integrals and ray tracing calculations. The amount of aberration correction can be adjusted relatively easy. The third order spherical and the first order chromatic aberration can be completely cancelled. In the zero current limit, a FW50 probe size of 1.0 nm at 1 kV can be obtained. This probe size is mainly limited by diffraction and by the fifth order spherical aberration.     

Third-order aberration theory of Wien filters for monochromators and aberration correctors

Third-order aberrations at the first and the second focus planes of double focus Wien filters are derived in terms of the following electric and magnetic field components – dipole: E₁, B₁; quadrupole: E₂, B₂; hexapole: E₃, B₃ and octupole: E₄, B₄. The aberration coefficients are expressed under the second-order geometrical aberration free conditions of E₂ = −(m + 2)E₁/8R, B₂ = −mB₁/8R and E₃R²/E₁ − B₃R²/B₁ = m/16, where m is an arbitrary value common to all equations. Aberration figures under the conditions of zero x- and y-axes values show very small probe size and similar patterns to those obtained using a previous numerical simulation [G. Martínez & K. Tsuno (2004) Ultramicroscopy, 100 , 105–114]. Round beam conditions are obtained when B₃ = 5m²B₁/144R² and (E₄/E₁ − B₄/B₁)R³ = −29m²/1152. In this special case, aberration figures contain only chromatic and aperture aberrations at the second focus. The chromatic aberrations become zero when m = 2 and aperture aberrations become zero when m = 1.101 and 10.899 at the second focus. Negative chromatic aberrations are obtained when m < 2 and negative aperture aberrations for m < 1.101. The Wien filter functions not only as a monochromator but also as a corrector of both chromatic and aperture aberrations. There are two advantages in using a Wien filter aberration corrector. First, there is the simplicity that derives from it being a single component aberration correction system. Secondly, the aberration in the off-axis region varies very little from the on-axis figures. These characteristics make the corrector very easy to operate.     

利用相位差异法检测镜面面形

为了验证相位差异波前检测器演示系统利用自带光源独立完成波前检测任务的能力,搭建了基于相位差异法检测镜面面形的实验平台。测试时在焦面和离焦面上同时采集短曝光图像,在已知离焦量的前提下解算出波前相位分布并恢复出目标,从而实现对大镜面像差的估计。为了进一步验证相位差异测量方法的准确性,对相位差异法与高精度的ZYGO干涉仪得到的测量结果进行了比较分析。实验结果表明:两种方法获得的面形误差分布及误差的峰谷值(PV)和均方根值(RMS)一致性很好,而波前RMS的测量精度达到了2.83/1 000λ。得到的结果表明提出的相位差异法能有效地检测出镜面的像差,且准确性很好。     

采用单位激励影响矩阵数值计算的瑞奇-康芒检测技术

在影响矩阵法瑞奇-康芒检验中,恢复被测面形的关键在于构建被检平面面形误差与系统波像差之间的Zernike系数影响矩阵。为了提高瑞奇-康芒法的检测精度,研究了采用单位激励法来精确计算影响矩阵的方法。分别重构平面镜仅包含某一种Zernike波像差下的系统波像差分布,经Zernike拟合得到该种Zernike像差的影响系数向量;由各Zernike像差的影响系数向量组成影响矩阵,然后用最小二乘拟合出被检平面面形。对口径为90mm的平面镜进行实际检验,在瑞奇角为26.5°与40.6°的情况下进行波前恢复,得到被检平面镜PV值为0.141 3λ,RMS为0.019 4λ。与直接采用平面参考镜检测相比,瑞奇-康芒法检测误差PV值为0.082 8λ,RMS为0.010 9λ。该方法能够精确生成影响矩阵,抑制了影响矩阵法中对大F数的依赖,可用于精确恢复平面镜面形。     

Analysis of spherical aberration of a water immersion objective: application to specimens with refractive indices 1.33–1.40

The method of using immersion medium to correct spherical aberration for water immersion objectives when the samples are not water is investigated. Spherical aberration is measured by an interferometer converted from a confocal microscope for samples with different refractive indices. When the proper refractive index of the immersion medium and thickness of cover slip are selected, the measured spherical aberration approaches zero. A theoretical model can be used for prediction of the immersion medium to correct spherical aberration for various samples. Using the thinnest available cover slip (100 μm), the zero spherical aberration condition can be applied to samples with refractive index as high as 1.40. Confocal images in the condition of almost no spherical aberration are included to demonstrate the improvement of axial resolution due to this correction.     

人眼波前像差客观测量的研究

分析波动光学中人眼像差的产生机理和波前像差的表示方式。运用Zernike多项式表示人眼波前像差函数,研究Zernike多项式与人眼波像差的对应关系以及一些高级像差对人眼成像质量的影响。通过对自适应光学中Zernike多项式重建波前理论的研究,重点分析了应用Hartmann-Shack波前传感器测量人眼客观像差并用变形反射镜矫正人眼像差的解决方案。对提高正常眼睛的视力和人眼屈光矫正手术具有重要的实验和临床价值。     

Adaptive aberration correction in a two-photon microscope

We demonstrate aberration correction in two-photon microscopy. Specimen-induced aberrations were measured with a modal wavefront sensor, implemented using a ferro-electric liquid crystal spatial light modulator (FLCSLM). Wavefront correction was performed using the same FLCSLM. Axial scanned ( x z ) images of fluorescently labelled polystyrene beads using an oil immersion lens show restored sectioning ability at a depth of 28 µm in an aqueous specimen.     

基于子孔径斜率离散采样的波前重构

由于现有评价与测试方法不能满足3~4m地基光电探测系统在不同仰角下对光学系统波前检测的需求,本文提出了基于子孔径斜率离散采样,再重构全口径波面轮廓的波像差测试方法。采用光学模拟与数学分析协同仿真的方法,研究了波面重构算法的不确定度以及扫描运动引起的子孔径倾斜误差、子孔径扫描位置误差、像点坐标测量误差与波前复原精度间的作用规律。仿真结果显示,迭代算法的相对误差ΔPV为0.002 8λ(λ=632.8nm),模式算法的相对误差ΔPV为0.002 7λ。当子孔径倾斜误差小于0.2″,波面重构误差ΔPV约为0.02λ。当子孔径采样位置精度优于0.2mm,其引入的波面重构误差小于0.04nm(PV);当子孔径像点坐标提取精度优于5μm,波面重构误差ΔPV约为0.03λ。研究结果表明,当考虑波面重构过程中的实际测量误差时,模式算法的误差容限较高,收敛性更好。此外,构建实际测试装置时,需引入角度监测与算法误差补偿机制,子孔径倾斜角度监测系统的测角精度需优于0.2″。     

大尺寸垂直梳齿驱动MOEMS扫描镜

提出了一种采用垂直梳齿驱动器驱动的大尺寸、大扭转角度、低驱动电压微光机电系统（MOEMS）扫描镜。理论分析了垂直梳齿驱动器的工作原理,研究了垂直梳齿的制作工艺,采用体硅加工工艺结合硅-硅键合工艺制作了垂直梳齿驱动的MOEMS扫描镜。制作的扫描镜镜面尺寸为3 mm×2 mm,谐振频率为1.32 kHz。测试表明,该扫描镜镜面具有很好的光学表面,其表面粗糙度的均方根只有8.64 nm;扫描镜在驱动电压为95 V时可以实现最大2.4°的扭转角度;测得其开启时的响应时间为1.887 ms,关断时的响应时间为4.418 ms。     

桌面97单元自适应光学系统性能测试

构建了一套桌面自适应光学系统性能测试系统,用以验证97单元自适应光学系统的校正能力。该测试系统主要由光源、快速控制反射镜、变形镜、Shack-Hartmann波前传感器、高速波前处理器、扰动相位屏等部件组成,分别利用干涉仪和Shack-Hartmann波前传感器的数据控制变形镜进行光路的展平校正,得到了系统的静态校正精度。然后,测试了精密跟踪系统的校正能力。最后,利用扰动相位屏模拟不同的大气扰动条件,以成像相机图像的斯特列尔比(SR)为指标,在不同目标亮度下测试了自适应光学系统的动态校正能力。测试结果显示:该97单元自适应光学系统的静态波像差校正精度的RMS接近λ/20;两种控制模式下精密跟踪系统的误差抑制带宽分别达到了15 Hz和39 Hz;系统在强湍流情况下,动态校正后的成像分辨率基本优于3倍衍射极限。由此表明,97单元自适应光学系统能够有效地校正像差,提高成像分辨率。     

全息扫描镜直线扫描分析及像差校正

介绍了全息扫描镜的原理,给出了等空间频率分布及变空间频率分布的全息扫描镜结构.基于全息图相位及相位传递函数方法,分析了全息扫描镜产生直线扫描条件,推导出记录子全息图各参数之间的关系,得出了利用短波长光记录子全息图,用长波长光再现,实现线性扫描的结果.提出了由于波长移动引起的像差校正方法.分析了摆动与偏心对扫描特性的影响.简介了所设计的变空间频率分布的全息扫描镜.     

Multi-probe scanning system comprising three laser interferometers and one autocollimator for measuring flat bar mirror profile with nanometer accuracy

This paper describes a multi-probe scanning system comprising three laser interferometers and one autocollimator to measure a flat bar mirror profile with nanometer accuracy. The laser interferometers probe the surface of the flat bar mirror that is fixed on top of a scanning stage, while the autocollimator simultaneously measures the yaw error of the scanning stage. The flat bar mirror profile and horizontal straightness motion error are reconstructed by an application of simultaneous linear equations and least-squares method. Measurement uncertainties of the flat bar mirror profile were numerically evaluated for different installation distances between the laser interferometers. The average measurement uncertainty was found to be only 10 nm with installation distances of 10 and 21 mm between the first and second, and first and third interferometers, respectively. To validate the simulation results, a prototype system was built using an X–Y linear stage driven by a stepper motor with steps of 1 mm along the X direction. Experiments were conducted with fixed interferometers distances of 10 and 21 mm, as in the simulation, on a flat bar mirror with a profile known to an accuracy of λ = 632.8 nm. The average value of two standard deviations (95%) of the profile calculated over ten experiments was approximately 10 nm. Other results from the experiment showed that the system can also measure the yaw and horizontal straightness motion errors successfully at a high horizontal resolution. Comparing with the results measured by ZYGO's interferometer, our measured data excluding some edge points showed agreement to within approximately 10 nm. Therefore, we concluded that our measurement profile has an accuracy in the nanometer range.     

光电跟踪系统Φ1000mm主镜的装调

1 000mm口径主镜的光机装调质量直接影响望远镜光学系统的成像效果。为了改善大口径光电跟踪系统的成像质量,本文对主镜的装调技术进行了研究。首先,对影响主镜面形精度的误差进行分配;其次,结合具体的主镜支撑结构的形式,采用典型装调方法对800mm口径主镜进行详细的装调研究,实时测得主镜的面形精度;最后,综合分析产生装调误差的来源,提出了一种加工、检测、装调一体化的高精度装调方法。该方法使得1 000mm主镜在装调后的面形精度波像差RMS值达到了λ/40,在提高装调质量的情况下显著提高了装调效率。     

Adaptive aberration correction using a triode hyperbolic electron mirror

A converging electron mirror can be used to compensate spherical and chromatic aberrations in an electron microscope. This paper presents an analytical solution to a novel triode (three electrode) hyperbolic mirror as an improvement to the well-known diode (two electrode) hyperbolic mirror for aberration correction. A weakness of the diode mirror is a lack of flexibility in changing the chromatic and spherical aberration coefficients independently without changes in the mirror geometry. In order to remove this limitation, a third electrode can be added. We calculate the optical properties of the resulting triode mirror analytically on the basis of a simple model field distribution. We present the optical properties-the object/image distance, z(0), and the coefficients of spherical and chromatic aberration, C(s) and C(c), of both mirror types from an analysis of electron trajectories in the mirror field. From this analysis, we demonstrate that while the properties of both designs are similar, the additional parameters in the triode mirror improve the range of aberration that can be corrected. The triode mirror is also able to provide a dynamic adjustment range of chromatic aberration for fixed spherical aberration and focal length, or any permutation of these three parameters. While the dynamic range depends on the values of aberration correction needed, a nominal 10% tuning range is possible for most configurations accompanied by less than 1% change in the other two properties.