Optical imaging deep inside scattering media remains a fundamental problem in bioimaging. While wavefront shaping has been shown to allow focusing of coherent light at depth, achieving it non-invasively remains a challenge. Various feedback mechanisms, in particular acoustic or nonlinear fluorescence-based, have been put forward for this purpose. Noninvasive focusing in depth on fluorescent objects with linear excitation is, however, still unresolved. Here we report a simple method for focusing inside a scattering medium in an epidetection geometry with a linear signal: optimizing the spatial variance of low-contrast speckle patterns emitted by a set of fluorescent sources. Experimentally, we demonstrate robust and efficient focusing of scattered light on a single source and show that this variance optimization method is formally equivalent to previous optimization strategies based on two-photon fluorescence. Our technique should generalize to a large variety of incoherent contrast mechanisms and holds interesting prospects for deep bioimaging.

中文翻译：

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使用散斑方差优化在散射介质中进行无创聚焦

在散射介质内部进行光学成像仍然是生物成像的基本问题。虽然波前整形已经显示出可以使相干光聚焦在深度，但是非侵入性地实现它仍然是一个挑战。为此，已经提出了各种反馈机制，特别是基于声学或非线性荧光的反馈机制。然而，仍然没有解决对具有线性激发的荧光对象进行深入的非侵入式聚焦的问题。在这里，我们报告了一种简单的方法，该方法可以利用线性信号在Epidetection几何结构中的散射介质内部聚焦：优化一组荧光源发出的低对比度斑点图案的空间方差。实验上，我们证明了散射光在单个光源上的鲁棒和有效聚焦，并且表明这种方差优化方法在形式上等同于以前基于双光子荧光的优化策略。我们的技术应该推广到各种各样的非相干对比机制，并为深部生物成像具有有趣的前景。