Deformable mirrors based on piezoelectric unimorph microactuator array for adaptive optics correction

This paper describes a piezoelectric deformable mirror (DM) for adaptive optics (AO) applications, with a 100 μm thick silicon mirror driven by 61 unimorph microactuators. Measurement results show that the stroke of the DM is ~ 7.4 μm at 100 V, and the resonance frequency is at 18 kHz. To demonstrate the correction capability of the DM, low-order Zernike modes up to 14th term were reproduced. Furthermore, a close-loop correction of laser beam in a 633 nm helium-neon laser system was performed. After system aberrations being compensated, a focal spot approximate to Airy disk was achieved.     

Atmospheric-induced aberration correction using feedback interferometer

We present a practical adaptive optics system based on feedback interferometry. The system consists a polarizing radial-sheared Sagnac interferometer incorporating a multi-segmented mirror for wavefront correction. Correction of atmospheric aberration is demonstrated.     

校正空间分块镜复位误差所需的最少自由度的确定

可收展式分块镜共相位成像技术是实现光学系统超大口径、超高分辨率成像的关键技术。分块镜复位误差会引起各子镜之间的共相位误差和整个拼接镜面的面形误差。合理确定校正分块镜复位误差所需的自由度具有非常重要的意义。计算机仿真分析了分块镜的复位误差对拼接镜面面形误差的影响。结果表明,所需的校正自由度的个数不仅与展开机构的复位精度有关,而且与分块镜镜面的几何参数有关。     

Aberration analysis of electron mirrors by a differential algebraic method

A differential algebraic (DA) method has been developed for the aberration analysis of electron mirrors. Since large ray slopes occur near the turning points in mirrors, the axial position is no longer suitable as the independent variable and the electron trajectory equation used in conventional lens theory is no longer feasible. A DA solution of the electron motion equation, wherein a single DA ray trace is performed on a non-standard extension of real number space called _nD_v, enables the aberrations of a mirror system to be obtained, in principle up to arbitrary order n, and with very high accuracy, due to the remarkable algebraic properties of _nD_v. With the DA method, the enormous effort to derive explicit formulae for the aberration coefficients of electron mirrors is avoided. A software package MIRROR_DA has been developed for the aberration analysis of electron mirrors, based on the DA method. Two examples of electron mirrors are presented. For the first example, for which the electrostatic and magnetic fields are represented by analytical models, the results computed with MIRROR_DA were shown to be in good agreement with those extracted by direct ray tracing, with relative deviations of less than 0.065% for all the primary aberration coefficients. The second example consists of a real magnetic lens and electrostatic mirror, with numerically computed fields, and from the results of MIRROR_DA, the spherical aberration coefficient C_s3 is almost cancelled out because of the correction effect of the mirror. The MIRROR_DA software is a novel, effective and precise tool for the aberration analysis of electron mirrors, capable of handling realistic and complicated systems of electron lenses and electron mirrors.     

环扇形分块主镜的波面拟合及重构方法研究

用有限元分析获得了环扇形分块主镜的镜面热变形数据,分别用圆域Zernike多项式和环扇域Zernike多项式对其进行了波面拟合,比较了用两种多项式的拟合精度。基于哈特曼-夏克波前传感器对由环扇形镜面热变形引起的畸变波前进行了模式法重构,分析了用上述两种多项式重构时矩阵条件数和测量误差对重构精度的影响。     

Modal correction for fiber-coupling efficiency in free-space optical communication systems through atmospheric turbulence

High-speed free-space optical communication systems have recently used fiber-optical components. The coupling efficiency with which the received laser beam can be coupled into a single-mode fiber is noticeably limited by atmospheric turbulence due to the degradation of its spatial coherence. Fortunately, adaptive optics (AO) can alleviate this limitation by partially correcting the turbulence-distorted wavefront. The coupling efficiency improvement provided by Zernike modal AO correction is numerically evaluated. It is found that the first 3-20 corrected polynomials can considerably improve the fiber-coupling efficiency. The improvement brought by AO is compared with that brought by a coherent fiber array. Finally, a hybrid technique that integrates AO and a coherent fiber array is proposed. Results show that the hybrid technique outperforms each of the two above-mentioned techniques.     

Theoretical analysis of imaging properties of a pressure-actuated deformable mirror for adaptive compensation of rotationally symmetrical wavefronts

Our work presents a theoretical analysis of aberration properties of a simple single-channel deformable mirror from both the aspect of modeling the shape of the mirror reflecting surface and the mechanisms of wave-front correction using such mirror. The proposed mirror can be used for a compensation of rotationally symmetrical wavefronts, e.g. focusing of optical beams, adaptive change of resonator parameters in laser technology, phase shifting, etc. The detailed analysis of possibilities of wave-front correction was performed.     

The system design and assemble for the high resolution telescope system with segmented aperture

A design method along with its results, for a space optical system with high resolution and wide field of view, is described. Such optical systems can be used in the infrared as well as visible configurations. The proposed design is based on an on-axis Ritchey-Chrétien system with corrected lens element while the primary mirror is a segmented aperture. Here the on-axis concept allows wide-field enabling a variety of observations designed for the multi-object spectrometer instruments, optimized for low scattering and low emission of light. The use of segmented mirrors in the optical system allows adopting any method for its fabrication purposes. Segment results are discussed and the image quality of the design based on these results is evaluated in this paper.     

基于近红外光谱的人眼像差校正系统中变形镜性能对比研究

对比分析了基于近红外光谱的人眼像差校正系统中两种微机械薄膜变形镜(OKO37单元和BMC140单元)的结构特征和空间特性,着重对变形镜的影响函数进行了主成分研究,建立了变形镜电压控制模型,并通过调整参数d确定变形镜最优控制模式。最后对Zernike单位模式波前像差和Thibos模式人眼波前像差进行拟合仿真实验,结果表明BMC140单元变形镜对Zernike各阶模式的拟合能力均为OKO37单元变形镜的2倍以上。对RMS均值为0.683λ(λ=0.785 μm)的Thibos模式人眼像差,BMC变形镜校正后残余像差RMS值为0.063λ,达到了光学系统的衍射极限(λ/14)。而OKO变形镜由于受相邻电极交连值大、电极分布密度小等因素的影响,其校正能力不及BMC变形镜,残余像差RMS值为0.168λ。本方法也可用于其他种类变形镜的性能评估。     

拼接式合成孔径光学系统的失调误差分析研究

拼接式合成孔径光学系统对系统误差分配有特殊要求,子镜失调将严重改变波前分布,影响系统成像。对一个拼接镜面的卡式原理演示系统进行了误差分析论证,并使用ZYGO干涉仪进行实测。结果表明,拼接镜面的波前误差RMS值和PV值有特殊关系,但在一定范围内仍可获得较好的MTF曲线。     

带边缘驱动的214单元单压电变形镜仿真与实验

为了提高用于天文自适应光学系统的单压电变形镜的校正能力,提出了一种直径为75 mm且包含214个单元的带边缘驱动的单压电变形镜,单压电变形镜的边缘由数个压电堆栈执行器支撑.首先,通过有限元方法对变形镜进行仿真建模,分析比较三点、六点能动支撑对变形镜性能的影响.之后制备了三点、六点边缘驱动的变形镜样机.最后,利用波前传感器测试了边缘执行器对低阶像差的校正能力.实验结果表明:在0~100 V电压下,三点能动支撑与六点能动支撑变形镜均可重构大于12μm的倾斜像差,对应的归一化残余误差小于0.06,六点致动对像散和三叶草像差也具有较好的校正能力,证明边缘执行器可提高单压电变形镜的校正能力.     

高功率固体激光构型验证装置波前畸变及补偿特性

为了优化高功率固体激光装置波前补偿系统的设计方案,基于构型验证装置开展了波前测试和补偿实验。实验结果显示,虽然等效钕玻璃片数大大增加,但由于主放采用了"U"型反转器技术,扣除离焦量后的静态和动态波前与原型装置相比没有显著提高,主要变化为离焦分量。若不采取任何补偿措施,会影响激光在前级滤波器的顺利过孔,造成近场缺光现象。实验中,为保证激光在动态发射时顺利过孔,采用了调节透镜的方式,使激光在各级滤波小孔位置有合适的预留量。同时,利用原型装置现有的小口径变形镜对扣除离焦后的像差进行补偿,减小激光在末级滤波小孔位置的像差。综合上述两种方法,成功解决了近场缺光的问题。针对未来高功率固体激光装置,伴随着光束口径和等效钕玻璃片数的增加,主放大器内的像差也会大幅度增加,采用上述调节透镜的方式可能无法兼顾静态和动态两种状态下的通光问题,需要在主放大系统内增加主动补偿措施,为腔镜变形镜的应用提供了实验依据。     

星间光通信系统中多样化波前畸变的小波重构

用小波变换方法对星间光通信中的多样化波前畸变进行重构,并分析了小波重构方法的两项参考指标：重构精度和重构算法复杂度。基于对这两项指标的综合考虑,提出一种最优小波基函数的选取方法。仿真数据表明,利用最优小波基函数选取方法对波前畸变进行重构,较之传统的Zernike多项式拟合方法,具有重构精度高且计算量小的特点。     

高功率固体激光构型验证装置波前畸变及补偿特性

为了优化高功率固体激光装置波前补偿系统的设计方案,基于构型验证装置开展了波前测试和补偿实验。实验结果显示,虽然等效钕玻璃片数大大增加,但由于主放采用了“U”型反转器技术,扣除离焦量后的静态和动态波前与原型装置相比没有显著提高,主要变化为离焦分量。若不采取任何补偿措施,会影响激光在前级滤波器的顺利过孔,造成近场缺光现象。实验中,为保证激光在动态发射时顺利过孔,采用了调节透镜的方式,使激光在各级滤波小孔位置有合适的预留量。同时,利用原型装置现有的小口径变形镜对扣除离焦后的像差进行补偿,减小激光在末级滤波小孔位置的像差。综合上述两种方法,成功解决了近场缺光的问题。针对未来高功率固体激光装置,伴随着光束口径和等效钕玻璃片数的增加,主放大器内的像差也会大幅度增加,采用上述调节透镜的方式可能无法兼顾静态和动态两种状态下的通光问题,需要在主放大系统内增加主动补偿措施,为腔镜变形镜的应用提供了实验依据。     

光束旋转90°多程放大系统的波前误差校正

光束通过神光-Ⅲ原型装置四程放大系统发生了90°旋转和扩束。在四程放大系统腔镜处放置变形镜校正系统像差是一种新的自适应光学方案，推导出被校正像差与变形镜面形之间的数学关系。理论推导表明，在扩束比大于1的前提下，腔镜处变形镜可以校正系统输出的任意类型的像差，且变形镜对应的面形唯一。理论分析和计算仿真说明该方案的校正能力与像差类型和扩束比有关，扩束比增大将增强变形镜校正像散的能力，但系统旋光消像散的能力也将减弱。     

Micro-electro-mechanical deformable mirrors for aberration control in optical systems

Controlling optical aberrations is one of the enduring problems in optics. Recent advances in adaptive optics for astronomical applications have shown the promise of adaptive optics technology for controlling aberrations. Micro-electro-mechanical deformable mirrors (MEM-DMs) offer an alternative to conventional adaptive optics which, due to the inexpensive nature of MEM-DM technology, will enable a wide range of commercial and scientific applications for optical wave front control. In this paper we describe MEM-DMs, present results of modelling the performance of an MEM-DM for optical aberration control, and present results of experiments to verify that MEM-DMs can control optical aberrations.     

Efficacy of motion artifact reduction in neonatal DW segmented EPI at 3 T using phase correction by numerical optimization and segment data swapping

Segmented echoplanar imaging (EPI) is a potentially valuable acquisition method for neonatal diffusion-weighted imaging (DWI) due to the lower acoustic noise levels as well as reduced blurring and distortion associated with it, as compared with single-shot EPI. Reduced acoustic noise may be important for the safety of neonates. However, little information regarding the efficacy of segmented EPI motion correction schemes is available for the neonatal population. We quantitatively assessed the efficacy of a postprocessing technique for motion artifact reduction involving phase correction by nonlinear optimization, alone and in combination with a novel method of utilizing a second data set (referred to as segment data swapping). These methods were applied to three-directional eight-segment echoplanar DW images obtained from 13 sedated neonates and to nine-directional DW images from 3 unsedated neonates. For comparison, the efficacy of the nonlinear optimization method was also evaluated in four adults. Motion correction efficacy was quantified using the motion artifact-to-signal ratio (ASR). The median, 70th percentile and 90th percentile ASR values obtained from neonatal three-directional DWI using nonlinear optimization alone were 2.8%, 4.6% and 9.6%, respectively. Efficacy improved (P<.005), particularly in dealing with the images most difficult to correct, when the phase correction by numerical optimization was combined with segment data swapping (median ASR=1.9%, 70th percentile ASR=2.7%, 90th percentile ASR=4.3%). Similar results were obtained for nine-directional diffusion tensor imaging. Nonlinear optimization alone applied to adult images showed significantly (P<.001) lower ASR values (median ASR=0.9%, 70th percentile ASR=2.1%, 90th percentile ASR=4.1%), demonstrating the greater challenge in DWI of neonates with segmented EPI. In conclusion, phase correction by nonlinear optimization provides effective motion correction for neonatal DW eight-segment EPI, especially when used in conjunction with segment data swapping.     

动态波前误差的自适应光学实时校正

本文报道了在实验室里用由21元面阵变形反射镜、横向剪切干涉仪和平行控制系统构成的自适应光学系统实时校正动态波前误差的原理和实验结果.     

四程放大系统腔镜位置变形镜的面形解

 根据在大型高功率固体激光装置中自适应光学技术的应用研究，将变形镜置于腔镜位置，有利于提高自适应光学系统的校正动态范围。基于变口径90°翻转四程放大系统的光路特点，从理论上比较完整地解决了四程放大系统腔镜位置变形镜面形解的存在性问题，并对口径变换比值(缩束比)与面形求解之间的关系问题进行了数值模拟，结果表明:只要缩束比小于1，对应系统连续波前畸变的腔镜位置面形解是存在的，且随着缩束比减小，解的收敛性增强。     

自适应光学控制系统对Kolmogorov湍流补偿的修正有效带宽

基于时间功率谱反演生成的Kolmogorov湍流时间序列, 模拟分析了自适应光学控制系统跟踪回路与高阶误差校正回路在有限误差-3 dB带宽、 有时间延迟情况下的闭环校正残余误差, 得出了系统的跟踪残余方差、高阶残余方差与误差-3 dB带宽的数值拟合结果, 修正了系统有效带宽的表达式, 使其能更精确地估计校正残余方差. 关键词： Kolmogorov湍流 Tyler频率 Greenwood频率 有效带宽