多层共轭自适应光学系统中等晕角的计算

介绍了多层共轭自适应光学(MCAO)系统的基本原理及其对提高自适应光学系统的等晕角的作用。介绍了用计算机模拟计算MCAO等晕角所用的数值方法,并给出了相应的算法。计算了在传统的自适应光学系统中的等晕角的大小以及采用多层共轭技术的自适应光学系统的等晕角的大小,并对二者进行了比较,说明了多层共轭自适应光学系统相对于传统的自适应光学系统在提高系统的等晕角方面的优越性。结果表明,在MCAO中,变形镜的个数越多其等晕角越大。     

分层校正自适应光学系统相位层析技术

假定大气湍流集中在两薄层内，借助分层大气相关长度与整个大气层相关长度的关系，给出待求相位分布与测量结果相关的超定方程组，进而构造残差方程组，并按最小二乘法原理导出正则方程组，通过求解这组正则方程，首次得到原超定方程组的最小二乘解。     

场共轭数值模拟研究

给出了一种考虑光源的强度分布后用两个变形镜头实现场共轭的算法,并对高斯光束进行了数值模拟,结果表明这种算法是有效的。变形镜平滑的表面可以剔除相位局部跳变,明显改善光强分布。对高斯光束,发射面相位面形状十分简单,易于用变形镜构造。本文还讨论了两变形镜之间距离的影响,最后指出如何改进现有算法。     

一种提高波前空间校正能力的组合变形镜自适应光学系统

提出了一种利用光学共轭关系,实现多变形镜空间匹配从而提高波前空间校正能力的自适应光学系统方案.通过理论分析给出了组合变形镜的面形描述方法,在此基础上建立了一套基于由两块相同方形排列变形镜构成的组合波前校正器的完整自适应光学实验系统.通过数值仿真研究了该系统对前35阶Zernike像差的校正效果,并且通过实验对比了组合变形镜和单一变形镜对实际静态像差的闭环校正效果.结果表明组合变彤镜可以等效为一多单元变形镜,在直接斜率控制算法下正常稳定闭环工作,校正效果明显优于单一变形镜.组合变形镜技术通过空间匹配实现了增加波前校正器驱动单元数和等效交连值,有效地提高了对波前的空间校正能力,因此可以代替高成本的单一多驱动器变形镜用于自适应光学系统中高阶像差的校正.     

单双层共轭系统的共轭高度对等晕角的影响

简要介绍了传统自适应光学系统的局限性和多层共轭自适应光学基本原理。模拟了单双层共轭校正系统的共轭高度,并结合平程与垂程(HV模型)两种传输状态对系统等晕角增益作了进一步的分析。对单层共轭系统,在20 km的传输距离内,在平程中整个区域都属于等晕角放大区,共轭高度的最佳位置在传输距离的中间（约10 km处）,等晕角取极大值,增益效果较好;但垂程中增益效果变差,且等晕角放大区也仅在3.6 km之内。对双层共轭系统来说,第1层共轭高度的变形镜主要对近距离畸变波前进行校正,并对整个传输距离的等晕角影响很大,是双层共轭系统的关键因素;第2层共轭高度对远距离等晕角影响较大。     

单双层共轭系统的共轭高度对等晕角的影响

 简要介绍了传统自适应光学系统的局限性和多层共轭自适应光学基本原理。模拟了单双层共轭校正系统的共轭高度,并结合平程与垂程(HV模型)两种传输状态对系统等晕角增益作了进一步的分析。对单层共轭系统,在20 km的传输距离内,在平程中整个区域都属于等晕角放大区,共轭高度的最佳位置在传输距离的中间（约10 km处）,等晕角取极大值,增益效果较好;但垂程中增益效果变差,且等晕角放大区也仅在3.6 km之内。对双层共轭系统来说,第1层共轭高度的变形镜主要对近距离畸变波前进行校正,并对整个传输距离的等晕角影响很大,是双层共轭系统的关键因素;第2层共轭高度对远距离等晕角影响较大。     

大气湍流的分层结构及自适应光学共轭校正

近期观察表明，在很多情况下，大气湍流主要集中在几个薄层中。将这些薄层用相位屏近似，由它们所引起的波前畸变可用分层共轭自适应光学系统进行补偿，从而使等晕角大大增加。本文对理论结果和实际的限制因素进行了较详细的讨论。     

基于模型的无波前探测自适应光学系统

基于波前梯度的二阶矩和修正后的远场强度分布近似呈线性关系,设计了一种基于模型的无波前探测自适应光学系统快速闭环控制算法。使用61单元变形镜、CCD成像器件等建立了自适应光学系统仿真平台,并以不同湍流强度下的波前像差作为校正对象,分析了这种基于模型的无波前探测自适应光学系统的收敛速度、校正能力及对不同像差的适应性。结果表明,基于模型的无波前探测自适应光学系统在快速收敛的同时,能够获得接近波前校正器件的理想校正能力。N阶模式像差校正时,系统只需要进行N+1次远场光斑的测量。和现有的各种无波前探测自适应光学系统控制算法相比较,基于模型的无波前探测自适应光学系统所需的测量次数大大减少。     

双变形镜自适应光学系统像差解耦研究

对由大行程变形镜和高空间频率变形镜组成的双变形镜自适应光学系统中的像差解耦原理和限定像差校正算法做了理论分析。认为在高空间频率变形镜的斜率响应矩阵中加入限定像差向量,根据直接斜率法分别计算出两个变形镜的控制电压,可以实现两个变形镜分别对低阶像差和高阶像差的闭环校正。仿真研究了19单元变形镜和61单元变形镜组成的双变形镜自适应光学系统对低阶像差和高阶像差分别校正的情况,结果说明双变形镜自适应光学系统的校正效果与理想行程的单变形镜自适应光学系统的校正效果相当,避免了制作同时具有大行程和高空间频率两个特征的变形镜。     

Sequence of phase correction in multiconjugate adaptive optics

The way in which the sequence of phase correction impinges on performance in multiconjugate adaptive optics systems is described. When multiple phase modulators with different conjugate ranges are used, the conjugate images of the phase modulators in the atmosphere must be reimaged in the reverse order post focus, and adaptive phase correction applied in this sequence for perfect amplitude and phase cancellation. Performing the correction without relay optics results in residual amplitude and phase aberrations. It is shown, by Monte Carlo simulations of Fresnel propagation, that the effects of wave optical propagation become nonnegligible at visible wavelengths and for large air masses.     

Solar adaptive optics system using an electromagnetic deformable mirror

A solar adaptive optics system has been improved by using a high-speed electromagnetic deformable mirror and adopting a modified sum-of-absolute-differences algorithm in wavefront sensing. Results of laboratory experiments clearly show that the use of the mirror raises the temporal performance of the system. In solar observations, wavefront compensation using solar granules as a target is realized.     

Lucky averaging: quality improvement of adaptive optics scanning laser ophthalmoscope images

Adaptive optics (AO) has greatly improved retinal image resolution. However, even with AO, temporal and spatial variations in image quality still occur due to wavefront fluctuations, intraframe focus shifts, and other factors. As a result, aligning and averaging images can produce a mean image that has lower resolution or contrast than the best images within a sequence. To address this, we propose an image postprocessing scheme called "lucky averaging," analogous to lucky imaging [J. Opt. Soc. Am. 68, 1651 (1978)] based on computing the best local contrast over time. Results from eye data demonstrate improvements in image quality.     

Second generation solar adaptive optics for 1-m New Vacuum Solar Telescope at the Fuxian Solar Observatory

A second generation solar adaptive optics(AO) system is built and installed at the 1-m New Vacuum Solar Telescope(NVST) of the Fuxian Solar Observatory(FSO) in 2015. The AO high-order correction system consists of a 151-element deformable mirror(DM), a correlating Shack–Hartmann(SH) wavefront sensor(WFS)with a 3500 Hz frame rate, and a real-time controller. The system saw first light on Mar. 16, 2015. The simultaneous high-resolution photosphere and chromosphere images with AO are obtained. The on-sky observational results show that the contrast and resolution of the images are apparently improved after the wavefront correction by AO.     

Ground-layer adaptive optics for the New Vacuum Solar Telescope:Instrument description and first results

Ground-layer adaptive optics(GLAO) has shown its potential for use in solar observation owing to its wide field-of-view(FOV)correction. A high-order GLAO system that consists of a multiple direction Shack-Hartmann wavefront sensor(WFS), a realtime controller with a multi-CPU processor, and a 151-element deformable mirror was developed for the 1-m New Vacuum Solar Telescope at Yunnan Observatories, Chinese Academy of Sciences. A hexagonal microlens with 9 × 8 subapertures is employed in the WFS. ...     

自适应光学波前校正器

报告了自适应光学波前校正器——多元分立式压电变形反射镜和两维高速压电倾斜镜的研究工作。讨论了这两类波前校正器的主要性能及其检测方法等，并给出了若干典型的检测结果。研制的１９单元度形镜已成功用于ＩＣＦ驱动器的波前校正，而２１单元变形镜已成功用于天文观测星体成像校正     

Retinal imaging with adaptive optics

Imaging the human retina in vivo is affected by the eye's natural aberrations, which limit the resolution of retinal images. Measuring these aberrations, including the high order ones, is possible using wavefront sensing techniques. A review of the rapid progress in this field is given. Once the aberrations are known, adaptive optics methods, developed for astronomical observing in the past 15 years, can be applied in order either to improve retinal imaging or to give hyper-vision to the subject. Progress in this domain is reviewed, and some original results are reported with a new instrument. Future applications are discussed, including a possible three-dimensional, high-resolution method to image the human retina in vivo.     

Solar cell performance improvement via photoluminescence conversion of Si nanoparticles

Photoluminescence (PL) conversion of Si nanoparticles by absorbing ultraviolet (UV) lights and emitting visible ones has been used to improve the efficiency of crystalline Si solar cells. Si nanoparticle thin films are prepared by pulverizing porous Si in ethanol and then mixing the suspension with a SiO2 sol-gel (SOG).This SOG is spin-deposited onto the surface of the Si solar cells and dries in air. The short-circuit current as a function of Si nanoparticle concentration is investigated under UV illumination. The maximal increase is found at a Si concentration of 0.1 mg/mL. At such concentration and under the irradiation of an AM0 solar simulator, the photoelectric conversion efficiency of the crystalline Si solar cell is relatively increased by 2.16% because of the PL conversion.