利用泽尼克系数求取衍射光栅的分辨本领

光栅分辨本领检测设备的焦距通常达几米甚至十几米,采用直接测量法难度大、成本高,利用衍射波前间接求取光栅分辨本领是解决该问题的有效途径之一。在光栅光谱成像傅里叶变换理论基础上,建立了利用泽尼克多项式拟合系数求解衍射光栅分辨本领的归一化模型,揭示了光栅衍射波前与分辨本领的求取关系,提出了依据泽尼克多项式拟合系数求取衍射光栅分辨本领的新方法。根据该方法实测了一块衍射光栅的分辨本领,并与直接测量法进行对比测试。结果表明该方法误差小于4.42%,降低了分辨本领的测试难度,是衍射光栅分辨本领求取的有效手段,应用于ZYGO干涉仪等仪器中,通过简单的波前测试即可得到定量的衍射光栅分辨本领指标。     

数字式激光平面干涉仪校准规范介绍

数字式激光平面干涉仪是用于测量光学元件面形和无焦光学系统波像差的光学仪器。为了统一数字式激光平面干涉仪测量量值，保证其测量结果的准确性和溯源性，编写数字式激光平面干涉仪校准规范。简要介绍了数字式激光平面干涉仪校准规范的构成，被校仪器的技术指标和校准方法等。     

米级口径经纬仪保护窗口镜面变形分析

为了精确分析外载荷作用下米级口径经纬仪保护窗口镜面变形,本文基于接触有限元理论建立了米级口径经纬仪保护窗口带摩擦接触的有限元分析模型,对比了线性刚性连接和非线性摩擦接触方法的差异。采用齐次坐标变换法去除刚体位移,得到米级口径经纬仪保护窗口镜面畸变数据,使用Zernike多项式作为光机集成分析的接口工具,并将Zernike多项式系数导入ZEMAX中,以波前像差RMS值衡量镜面变形对成像质量的影响,并与干涉仪检测结果进行比较。考虑摩擦接触条件得到的保护窗口镜面波前像差RMS值为38.095 nm、PV为205.027 nm,使用干涉仪检测得到的保护窗口镜面波前像差RMS值为40.626 nm、PV值为235.654 nm。实验结果表明,考虑摩擦接触条件的仿真实验与干涉仪检测实验的镜面波前像差RMS值偏差为6.23%,能更准确地反映米级口径保护窗口镜面变形。     

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。     

新型离轴反射变焦距光学系统的多视场检测方法

基于对离轴反射变焦距光学系统进行计算机辅助装调研究, 需要检测离轴反射变焦距系统各个视场的波像差, 除零度视场外, 获得包括其他视场的波像差有助于提高计算机辅助装调的准确性, 但是目前已有的波像差检测方法往往只能获得系统零度视场的波像差. 本文针对这个难题提出了一种检测离轴反射变焦距光学系统各个视场波像差的方法, 并应用于离轴三反变焦距光学系统的各视场波像差仿真检测. 该方法在传统自准直干涉法的基础上进行改进, 关键在于采用变形镜代替扫描的平面镜, 并采用夏克-哈特曼波前传感器代替干涉仪, 配合精确标定的激光器光源阵列, 可以实现对离轴三反变焦距光学系统的多视场波像差同时检测. 由理论分析和仿真模拟得出, 该系统在视场(0°, 3°), (0°, 4.2°), (0°, 5.5°), (0°, 7°), (0°, 9.8°), (0°, 14°)处经过变形镜补偿后的剩余波像差的RMS值分别为0.00039λ, 0.00075λ, 0.0024λ, 0.00017λ, 0.00053λ, 0.0057λ, 分析仿真结果表明此检测方案是可行的, 且适用于离轴反射变焦距系统的计算机辅助装调技术的研究.     

卡塞格林系统光学装调技术研究

介绍卡塞格林系统非球面主镜使用三坐标测量仪进行定心装调的方案。系统的主镜口径为300 mm,需要使用结构胶进行胶结固定,选用微应力粘接方法,将胶层粘接应力与热应力变形控制在极小的范围内。利用ZYGO干涉仪获得光学系统的波前信息,将测得的波相差转化为初级像差,根据光学系统失调量与像差的关系对卡塞格林系统进行计算机辅助装调。调试后,系统的RMS值达到0.10,分辨率达到1以内,检测结果表明:该系统的成像质量接近理论衍射分辨率,该方案可以实现快速定心,并且能够满足计算机辅助装调对定心精度的要求。     

A modified phase diversity diffraction wavefront sensor with a grating

The phase diversity wavefront sensor is one of the tools used to estimate wavefront aberration, and it is often used as a wavefront sensor in adaptive optics systems. However, the performance of the traditional phase diversity wavefront sensor is limited by the accuracy and dynamic ranges of the intensity distribution at the focus and defocus positions of the CCD camera. In this paper, a modified phase diversity wavefront sensor based on a diffraction grating is proposed to improve the ability to measure the wavefront aberration with larger amplitude and higher spatial frequency. The basic principle and the optics construction of the proposed method are also described in detail. The noise propagation property of the proposed method is also analysed by using the numerical simulation method, and comparison between the diffraction grating phase diversity wavefront sensor and the traditional phase diversity wavefront sensor is also made. The simulation results show that the diffraction grating phase diversity wavefront sensor can obviously improve the ability to measure the wavefront aberration, especially the wavefront aberration with larger amplitude and higher spatial frequency.     

A modified phase diversity wavefront sensor with a diffraction grating

Phase diversity wavefront sensor is one of the useful tools to estimate the wavefront aberration, and it is often used as a wavefront sensor in adaptive optics system. However, the performance of the traditional phase diversity wavefront sensor is limited by the accuracy and dynamic ranges of the intensity distribution at focus and defocus positions of the CCD camera. In this paper, a modified phase diversity wavefront sensor based on a diffraction grating is proposed to improve the ability to measure the wavefront aberration with larger amplitude and higher spatial frequency. The basic principle and the optics construction of the proposed method are also described in detail. The noise propagation property of the proposed method is also analysed by using the numerical simulation method, and comparison between the diffraction grating phase diversity wavefront sensor and the traditional phase diversity wavefront sensor is also made. The simulation results show that the diffraction grating phase diversity wavefront sensor can obviously improve the ability to measure the wavefront aberration, especially the wavefront aberration with larger amplitude and higher spatial frequency.     

Phase diversity for calibrating noncommon path aberrations of adaptive optics system under nonideal measurement environment

When the defocus cannot be measured and the wavefront solution set is restricted by a multi-channel, some practical problems exist in the calibration of the noncommon path aberrations of the adaptive optics system. To solve these problems, an evaluation function of phase diversity algorithm is constructed in this paper. We use the method that the estimated aberration and the modulated deformable mirror iterate each other to make up the nonideal measurement environment. Then the ill-pose problem of the solution by phase diversity, produced as relaxing constraints of the diversity defocus on the wavefront solution set, is solved. We have adopted the proposed method to measure the noncommon path aberrations of the adaptive optics system on a 1.23 m telescope. Experimental results demonstrate that wavefront solution is more accurate and the whole imaging quality is improved effectively by using the deformable mirror to compensate the aberration measured.     

近红外瞬态脉冲波前高精度干涉检测技术

惯性约束聚变(ICF)系统中高能瞬态脉冲激光由于脉冲时间短、能量高、波前畸变大,通常的检测方法难于检测脉冲激光波前。提出了一种基于空间相位调制技术可用于近红外瞬态波前高精度检测的环形径向剪切干涉仪。该系统可以以30~150 mm的圆瞳和方瞳口径、对波长为1064 nm的近红外纳秒级脉宽的脉冲激光波前实现共路、无参考面的瞬态、高精度的检测。系统的波前重构理论经过计算机仿真验证,精度达1/1000λ以上;检测结果与ZYGO数字波面干涉仪进行了比对,峰谷值、均方根值均优于1/15λ,并具有很好的可重复性。该系统目前已用于惯性约束聚变系统的脉冲检测,并且该技术适用于各种可见光和红外波段激光。     

子孔径合成光学成像系统像质评价研究

由于子孔径合成光学成像系统出瞳波前离散,成像特征有异于常规光学系统.对比了两种子孔径合成光学成像系统的像质评价方法,其一是直接利用干涉仪实测获得的整体出瞳波面参量,拟合成泽尼克多项式,通过快速傅里叶变换获得光学系统的调制传递函数;其二是对子出瞳波面在像面复振幅分布的衍射直接积分叠加计算系统调制传递函数.对于离散出瞳波前,拟合的泽尼克多项式不可避免有较大误差,由此计算获得的调制传递函数与实际测量值有较大区别.设计并制造了一个三子镜合成的成像光学系统,在此基础上用ZYGO GPI干涉仪验证并对比了使用两种方法对像质计算的特点.结果表明,子出瞳波面直接衍射积分叠加法的精度更高,但计算量大,且要获得更高的像质评价精度,应使用更适于表达离散不规则形状子出瞳波前的波函数.     

Aberration theory of plane‐symmetric grating systems

Aberration theory of plane‐symmetric optical systems of mirror and grating has been developed based on the wavefront aberration method. A toroidal reference wavefront surface is used to define the wavefront aberration. Based on the ray geometry, the coordinate mapping relationships of the ray between the optical element and the incident and aberrated wavefronts are derived using a polynomial‐fit method; this enables the resultant coefficients of the wavefront and the transverse aberration to be kept to the fourth‐order accuracy of the aperture‐ray coordinates. By setting up the transfer equations of the field and aperture rays, the contribution to wavefront aberrations from each mirror and grating can be added to make the aberration calculation of multi‐element systems feasible. The theory is validated by the analytic formulae of the spot diagram.     

Measurement of transient near-infrared laser pulse wavefront with high precision by radial shearing interferometer

It is hard to measure the transient near-infrared pulse laser wavefront in inertial confinement fusion (ICF) system by conventional methods for its short pulse width, large energy, high power and large distortion. A circular radial shearing interferometer based on spatial phase modulation is proposed to measure the transient near-infrared laser pulse wavefront with high precision. Transient, highly precise measurement for near-infrared laser pulse wavefront, with pulse width of nanometer scale and central wavelength of 1064 nm, can be carried out with common path, no reference plane. The theory of wavefront reconstruction has been validated by the computer simulation, and an error less than 1/1000λ is obtained. Comparing with the results of ZYGO interferometer, an error less than 1/15λ for both peak valley and root mean square value, is gained with good repeatability. The system has already been used in the ICF system to test the pulsed laser wavefront, and can also be applied to other lasers of visible and infrared wavelengths.     

遗传算法在自适应光学系统中的应用

为了校正激光光束的波前像差,建立了一套无需直接探测波前信息的自适应光学(AO)系统模型,提出了一种基于实数编码的高斯变异的遗传算法(GA)用来控制61单元压电变形镜补偿波前像差,并仿真利用此算法控制61单元变形镜校正由变形镜本身产生的像差。结果表明,这种算法能够找到补偿各种像差所需的变形镜的最优面型。像差校正后,焦平面的峰值光强最多能够提高30倍。环围斯特尔比值(Strehl ratio)最多能够从校正前的0.032提高到0.96,变形镜61个驱动器后的电压值收敛性能良好。     

渐进多焦点镜片波前像差的扩束测量方法

利用波前传感器测量自由曲面镜片时,由于自由曲面镜片的直径通常大于波前传感器的接收孔径,主要采用子孔径拼接技术测量镜片的波前像差。针对子孔径拼接技术测量中存在着操作繁琐、数据处理量大等问题,提出渐进多焦点镜片波前像差的扩束测量方法,得到渐进多焦点镜片中央直径为22 mm圆形区域内的波前像差。为了验证试验的可靠性,将测量得到的波前像差泽尼克表述中的离焦项转换为球镜度,与条纹偏折法测量得到镜片的球镜度进行对比实验,实验结果证明了渐进多焦点镜片波前像差的扩束测量方法可以用于渐进多焦点镜片波前像差的检测。     

哈特曼夏克传感器的泽尼克模式波前复原误差

利用哈特曼－夏克传感器测量圆孔径内波像差时，通常使用泽尼模式复原算法。推导了一般情况下哈特曼－夏克传感器泽尼克模式波前复原误差的计算公式。用哈特曼－夏克传感器测量一个像差板的随机静态像差，通过与ZYGO干涉仪的测量结果比较，得到不同泽尼克模式复原阶数下的波前复原误差的实验结果，并与理论计算结果进行了对比。     

非球面数字波面检测技术

提出了一种快速检测浅度非球面（非球面度小于0.01 mm）的方法,该方法无需补偿器或其他辅助光学元件进行零位补偿。用移相干涉仪直接测量正轴或离轴的浅度凹非球面,剔除平移、倾斜、失焦等调整误差后,得到实际被测镜面的面形分布数据;根据正轴或离轴的浅度凹非球面矢高方程计算理想非球面的面形分布数据,得到理论波面数据,用实测的面形分布数据减去理论的面形分布数据即可得到被检非球面的剩余波像差,即面形误差。利用该方法测量了一口径为135 mm的双曲面,并用零位补偿法加以验证。两种方法的检测结果精度相当,说明数字波面法可实际应用于正轴或离轴的浅度凹非球面的检测。     

Method of reconstructing wavefront aberrations from the intensity measurement

A method for reconstructing wavefront aberrations from intensity measurements in the focal plane of a focusing optic is presented. This reconstruction method is simple, fast, and accurate in reconstructing wavefront aberrations because it uses the inverse Fourier transform of an intensity distribution in the focal plane with a reference electric field. The validity of the reconstruction method is demonstrated by computing a wavefront aberration from the intensity distributions in the focal plane.     

基于矢量波像差理论的两反光学系统装调研究

 为了实现对两反光学系统的精密装调,提出一种基于矢量波像差理论和波像差检测技术对失调量精确求解的装调方法。使用矢量波像差理论,将已设计的两反光学系统参数、失调量和失调光学系统的波像差之间建立方程;然后通过干涉测量法得到某一个视场的干涉图,利用条纹分析软件得到表征失调系统三阶彗差和三阶像散的泽尼克项系数,将泽尼克项系数代入方程从而求解出失调量。运用此方法对4 m口径RITCHEY-CHR-TIEN结构的天文望远镜进行模拟装调,最终求解的失调量与引入的失调量结果相互吻合,说明该装调方法正确。     

VIRGO mirrors: wavefront control

The Franco-Italian VIRGO program to detect gravitational waves requires large mirrors whose optical properties are extremely severe: absorption and scattering <1ppm at 1064nm, wavefront homogeneity of 9nm RMS on Ø100mm. To achieve this performance on the wavefront, we have developed an experimental method to correct the wavefront shape to be as plane as possible. A thin silica layer is added through a mask by sputtering, where it is necessary on the surface, on the last layer of the multilayer. A phase retardation is produced. The wavefront is measured before and after correction with a Zygo interferometer. The first test has been done on Ø80mm mirror at 633nm. The wavefront peak to valley goes from 34 to 14nm. At this level, we are limited by the interferometer accuracy and repeatability. The optical property modifications due to the corrective coating are small (at 1064nm) or easy to overcome. The corrected wavefront includes at the moment the reference flat of the interferometer, so the measurements are not absolute. But the feasibility of this correction method is proved and it is powerful.