自适应光学波前传感技术分析

自适应光学波前传感技术
主要内容
1、哈特曼夏克波前传 感 2、金字塔波前传感
3、曲率波前传感 都是非相干波前测量系统
工
作
成
哈特曼夏克波前传感
绩
Evolution of the Hartmann test – standard devices for measuring wavefront slope errors
Hartmann test
One method for testing a lens or mirror employs an opaque mask with holes placed behind the optical element under test.Each of the holes acts as an aperture, and since the light passing through the lens is converging, the image produced is an array of spots.With proper calibration, the position of the spots is a direct indication of the local wavefront tilt at each hole, and thus is a description of the lens quality.This test is called the Hartmann test.
be large enoughr0 to resolve the isoplanatic patch.During 哈
high turbulence, is small and anisoplanatism degrades
特
the process.Hardy discusses details of this large-versussmall subaperture trade for various optical and atmospheric
哈
aberrations will distort the pattern on the quadcell and
特 曼
decrease tilt-measurement accuracy.
夏
克
Correlation Tracker
When the wavefront source is an extended object, a centroid measurement, like that in a Shack–Hartmann sensor, is meaningless.Each subaperture contains a small image of the entire object with the image shifted according to subaperture tilt.To overcome this problem, one image IR (x) is chosen as a reference. The cross-covariance between each image I is calculated by
breadboard correlation tracker built by the Solar Physics
哈
Group at Lockheed Palo Alto Research Laboratory for
特
image motion compensation on a space borne solar
records a cross-correlation of the mask and the scene in
each subaperture.Even if the object remains unresolved,
the problems associated with subaperture higher-order
曼
multiple pixels used for spot position (wavefront tilt)
夏ቤተ መጻሕፍቲ ባይዱ
determination.
克
Extended object
If that source is an extended object, the shape of the
object is convolved with the subaperture diffraction
subaperture, an optical correlation can be used.
Von der Luhe suggested the use of an addressable
optical mask, whose transmission is derived from the
image of the reference scene.The Hartmann detector array
sun.Cross-correlation algorithms are used to determine
wavefront tilts, rather than centroids. Increases in the
speed of two- dimensional detector arrays and
曼 夏 克
Hartmann wavefront sensor
Hartmann wavefront sensing technique.
哈
A Hartmann sensor is composed of an array of lenses
特
for wavefront division and typically a CCD array with
一起绕被测物镜的光轴转动。P1 和P2 的主截面彼此平行，并与光轴方向一致。
当P1 沿径向平移时可实现对被测物镜出射光束的离散采样。采样光束通过P1
和P2 后在相对被测物镜固定不动的CCD相机光敏面上生成一个艾利斑。测出
P1 处于光瞳面内不同位置 (, ) 时所对应的艾利斑质心坐标和相对偏移量的 哈
where x is the 2-D spatial coordinate,δ is the 2-D image
displacement, F and F is the forward and inverse Fourier
transforms, and * indicates the complex conjugate.This method
optical processing are used.
For atmospheric turbulence compensation, the local
wavefront tilt must br0e measured accurately in each
subaperture of size .To do this, the subaperture must
a field-of-view shifted Shack–Hartmann wavefront sensor
can be used.In solar imaging applications, each
subaperture sees an image of the extended source, the
microprocessors have led to developments that utilize
these advantages.
The first such system to successfully compensate image
motion of a ground-based solar telescope was the
pattern on the quadcell.Intensity variation can seriously
degrade the measurement accuracy of the centroid.To
remove the effects of extended objects resolved by the
要的应有价值。
本方法的技术可行性强，容易实现；测量灵敏度与一般干涉
法相当，但对光源的单色性和工作环境并无苛刻要求，因此便于
推广应用。
本方法由于采用了机械扫描采样方式，一次测量需时几分钟，
所以不适用于以校正大气湍流为目的的自适应光学系统。
哈
特
曼
夏
克
自基准哈特曼波前传感器
图中五棱镜 P1 可单独沿被测物镜光瞳的半径方向平移,也可与五棱镜 P2
曼
telescope.
夏 克
自基准哈特曼波前传感器
根据波前径向斜率测量原理,提出一种利用五棱镜扫描方法实
现了新型自基准哈特曼波前传感器，其突出优点和特点是毋需任
何外部信标或标准大平面反射镜提供工作基准。这对主动光学新
技术的空间应用有重要意义。对大型天文望远镜光学系统裝校检
测和大口径高精度抛物面反射镜以及平行光管等的检测也具有重
哈 特 曼 夏 克
Hartmann wavefront sensor
The Hartmann wavefront sensor is shown in below
figure .The wavefront is divided by a mask, as in the
classical test, an array of gratings, or an array of
哈 特 曼 夏 克
History
Shack placed lenses in the holes, which increased the light-gathering efficiency of the mask and, with the spots focused, reduced the disturbing diffraction effects of the holes. A lens array for this purpose was first manufactured in 1971.Members of the astronomy community began to use this sensor in the late 1970s for testing of large telescope optics.Some astronomers use the term Hartmann–Shack (or Shack–Hartmann) wavefront sensor, but many shorten it to simply Hartmann sensor.
has been applied in solar telescopes where photons are plentiful,
but the object is large.
哈
特
曼
夏
克
Daytime astronomy
For daytime astronomy with large background radiation,
径向分量，由下式即可求得被测物镜出射波前斜率的径向分量
特
曼
夏
克
自基准哈特曼波前传感器
理论分析和计算机仿真结果表明，在采样密度足够的情况下，根据已知波 前径向斜率分量的离散采样值也完全可以以足够高的精度重构出原始波面 的形状;如果径向斜率离散采样值包含有一定的随机误差，也仍能重构出精 度与波前径向斜率采样精度相当的波前形状。用泽尼克径向斜率多项式作 最小二乘拟合具体过程如下。对波面上每一点的径向斜率测量数据可分别 写出
哈
式中
即为单位圆上 点处第n项Zernike多项式的径向斜率值，
也就是以Zernike多项式形式表示的基元波面的斜率值。
transmissive lenses.Each of the beams in the
subapertures is focused
onto a detector.To detect the position of the spot, various
forms of modulation, detector geometry, and electro-