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dOTF是通过简单直接的技术获取光瞳面成像的波前相位和复振幅,两个点扩散函数(Point Spread Function,PSF)图像的傅里叶变换之差近似于光学传递函数(Optical Transfer Function,OTF)对光瞳掩模(pupil mask)的导数,而 OTF导数的几何意义为翻转对称且存在部分重叠的共轭光瞳图像,针对不重叠部分的光瞳可通过相位和振幅进行检测,针对重叠部分的光瞳,dOTF引入部分遮挡,减小光瞳重叠区域内二次项影响的方法,计算得到光瞳面的差分光学传递函数,估算整个光瞳面的相位和振幅分布,得到光学系统的波前分布[10-11]。本质是利用两幅PSF图像的傅里叶变换之差(分别取全部光瞳面和部分遮挡的光瞳面)计算光瞳面(pupil field)的相位分布。因为PSF是光瞳面的二次泛函,傅里叶变换后所得的OTF本质上为非线性函数,dOTF则是通过微分方法将OTF的二次泛函变为线性的过程[12]。
设光瞳掩模后复振幅为
$u\left( x \right)$ :$$u\left( x \right) = \Pi \left( x \right){u_0}\left( x \right)$$ (1) 式中:
$\Pi \left( x \right)$ 为光瞳掩模函数;${u_0}\left( x \right)$ 为入射光瞳复振幅。由傅里叶光学可知,
${\cal{H}}\left( \xi \right)$ (OTF)为${h_f}\left( x \right)$ (PSF)的傅里叶变换:$${\cal{H}}\left( \xi \right) = {\cal{F}}\left\{ {{h_f}\left( x \right)} \right\}$$ (2) OTF在光瞳场内可表示为:
$${\cal{H}}\left( \xi \right) = \frac{1}{{{{\left( {2\pi } \right)}^2}}}\int {{{\rm{e}}^{ - j\kappa \xi }}{{\left| {u\left( x \right)} \right|}^2}} {\rm{d}}x$$ (3) 式中:
$\xi $ 为空间频率。dOTF中被遮挡部分的光瞳函数变化可由公式(4)表示:$$\Pi '\left( x \right) = \Pi \left( x \right) + \Delta \Pi \left( x \right)$$ (4) $\Delta {\cal{H}}\left( \xi \right)$ (dOTF)可表示为:$$ \begin{split} \Delta {\cal{H}}\left( \xi \right) = &{{\cal{H}}_{\Pi {\rm{ + }}\Delta \Pi }}\left( \xi \right){\rm{ - }}{{\cal{H}}_\Pi }\left( \xi \right) =\\ & u\Delta {u^{\rm{*}}}{\rm{ + }}\Delta u{u^{\rm{*}}}{\rm{ + }}\Delta u\Delta {u^{\rm{*}}} \\ \end{split} $$ (5) 当不考虑重叠区域点时,最终求得光瞳面的相位
$\vartheta \left( \xi \right)$ 和振幅$A\left( \xi \right)$ 可由公式(6)~(7)表示:$$\vartheta \left( \xi \right) = \arg \left\{ {\Delta {\cal{H}}} \right\}$$ (6) $$A\left( \xi \right) = \left| {\Delta {\cal{H}}} \right|$$ (7)
Large aperture transmission optical element detection method based on dOTF
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摘要: 为了保证在重力变化下大口径巡天望远镜透镜组的成像质量,需要研究一种可以适用于大口径透镜组的波前检测方法,用于实现系统装调检测。首先,基于差分光学传递函数(differential optical transfer function,dOTF)建立了一套波前对准检测技术,在此基础上,分析了运算过程中相位解缠,CCD探测噪声以及大气扰动对检测算法造成的误差影响,结果表明检测误差分别小于10%、1%和2.5%,经过叠加可得整体的测量精度约为10.3%,满足一般大口径大视场检测系统设计指标。最后针对80 mm的透射式系统进行验证,由实验结果得到波前检测主要成分为彗差,与理论分析结果一致,符合几何光学预测结果。Abstract: To ensure the corrector lens meet the imaging quality of design requirements under the change of gravity, the large aperture corrector lens needs a wavefront detection method for implementing system adjustment detection. Firstly, on the basis of the differential optical transfer function (dOTF), the wavefront alignment detection technology was proposed consequently. Next, the error effects caused by the phase resolution, CCD detection noise and atmospheric disturbance on the detection algorithm were analyzed. The results show that the detection error is less than 10%, 1% and 2.5%. The overall measurement precision obtained by superposition is about 10.3%, which meets the design indexes of general large aperture survey design requirement. Finally, the accuracy of the detection method in the 80 mm transmission system was verified by the experiment. From the experimental results, the main error of wavefront detection is coma, which is consistent with the theoretical analysis results and consistent with the geometric optical prediction results.
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