本文提出自适应光学成像系统中哈特曼波前探测器电子倍增增益的自适应控制方法,以使哈特曼波前探测器保持较高的信噪比同时避免亮度过饱和.利用亮度接近哈特曼饱和值的光源作为被观测目标,探测到的光斑阵列中有一个最高亮度值Im,统计200帧～500帧中的Jm,计算其相对统计帧数的均值Im、Im相对Im的均方差值σm;设定理想最高亮度值-Ims比饱和亮度低3.0σm～3.2σm;再将光斑的亮度最大值相对一帧阵列中的光斑数计算平均值记为Ia,实时监测Ia;依据信号强度I与增益G的线性关系,事先测得哈特曼波前探测器的技术特征参数ka、km和理想最高亮度值Ims,即可以由当前帧探测数据Ia和增益Ga计算得到所需调整的增益值Gms.
Electron multiplying charge-coupled-device (EMCCD) in Hartmann wavefront sensor (WFS) makes the SNR higher than the ordinary CCD.However,a fixed EM gain may not work when the brightness of the observed target changes in large ranges within a few minutes.Thus,an adaptive control method of the Hartmann WFS' gain is proposed.The control value is the average of the maximum signals of all the light spots in a frame.The goal value for control is predetermined based on the linear relation of the signal with the EM gain and the number of photons collected in sub-apertures.The self-protection for brightness super saturation of the EMCCD has to be considered for the goal value.Simulations and experiments indicate that the proposed control method keeps the sensing in a high SNR without the self-protection of the EMCCD occurred even when the target brightness changes in sine curves.
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