浑浊介质中隐藏物体的偏振鉴别成像：通过随机共振检测弱正弦波
Polarization Discrimination Imaging of objects hidden in turbid media: Detection of weak sinusoids through Stochastic Resonance
摘要：
在偏振鉴别成像中，来自旋转分析器的正弦曲线的幅度，代表残留偏振光并携带关于物体的信息，在锁定放大器的帮助下被检测到。当浊度增加超过一个水平时，锁定放大器无法检测到透射光中的微弱正弦分量。在这项工作中，我们采用了随机共振的原则，并使用一个3电平量化器来检测正弦波的幅度，这是无法检测与锁定放大器。在使用三电平量化器时，我们采用了三种不同的方法来提取弱正弦信号的幅度：（a）使用量化输出的概率来跨越量化器中的某个阈值;（b）最大化量化的检测强度数据的似然函数;以及（c）得到检测输出中的预期功率的表达式，并将其与实验测量的功率进行比较。我们已经证明了这些非线性估计方法通过检测隐藏的目标从偏振歧视成像系统的实验数据。当浊度增加到L/l = 5.05（l是传输平均自由程，L是混浊介质的厚度）时，通过所提出的方法分析的数据从估计的振幅揭示了对象的存在。仅使用锁定放大器系统是不可能的。
英文摘要：
In Polarization Discrimination Imaging, the amplitude of a sinusoid from a rotating analyzer, representing residual polarized light and carrying information on the object, is detected with the help of a lock-in amplifier. When turbidity increases beyond a level, the lock-in amplifier fails to detect the weak sinusoidal component in the transmitted light. In this work we have employed the principle of Stochastic Resonance and used a 3-level quantizer to detect the amplitude of the sinusoids, which was not detectable with a lock-in amplifier. In using the three level quantizer we have employed three different approaches to extract the amplitude of the weak sinusoids: (a) using the probability of the quantized output to crossover a certain threshold in the quantizer (b) maximizing the likelihood function for the quantized detected intensity data and (c) arriving at an expression for the expected power in the detected output and comparing it with the experimentally measured power. We have proven these non-linear estimation methods by detecting the hidden object from experimental data from a polarization discrimination imaging system. When the turbidity increased to L/l = 5.05 (l is the transport mean-free-path and L is the thickness of the turbid medium) the data through analysis by the proposed methods revealed the presence of the object from the estimated amplitudes. This was not possible by using only the lock-in amplifier system.
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