Light-scattering methods are widely used in soft matter physics and biomedical optics to probe dynamics in turbid media, such as diffusion in colloids or blood flow in biological tissue. These methods typically rely on fluctuations of coherent light intensity, and therefore cannot accommodate more than a few modes per detector. This limitation has hindered efforts to measure deep tissue blood flow with high speed, since weak diffuse light fluxes, together with low single-mode fiber throughput, result in low photon count rates. To solve this, we introduce multimode fiber (MMF) interferometry to the field of diffuse optics. In doing so, we transform a standard complementary metal-oxide-semiconductor (CMOS) camera into a sensitive detector array for weak light fluxes that probe deep in biological tissue. Specifically, we build a novel CMOS-based, multimode interferometric diffusing wave spectroscopy (iDWS) system and show that it can measure $\sim 20$ speckles simultaneously near the shot noise limit, acting essentially as $\sim 20$ independent photon-counting channels. We develop a matrix formalism, based on MMF mode field solutions and detector geometry, to predict both coherence and speckle number in iDWS. After validation in liquid phantoms, we demonstrate iDWS pulsatile blood flow measurements at 2.5 cm source-detector separation in the adult human brain in vivo. By achieving highly sensitive and parallel measurements of coherent light fluctuations with a CMOS camera, this work promises to enhance performance and reduce cost of diffuse optical instruments.

中文翻译：

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高度平行的干涉扩散波谱仪，用于监测脑血流动力学

光散射方法广泛用于软物质物理学和生物医学光学中，以探测混浊介质中的动力学，例如胶体中的扩散或生物组织中的血流。这些方法通常依赖于相干光强度的波动，因此每个检测器无法容纳多个模式。这种局限性阻碍了高速测量深层组织血流的努力，因为弱的漫射光通量以及低的单模光纤吞吐量会导致低的光子计数率。为了解决这个问题，我们将多模光纤（MMF）干涉术引入了散射光学领域。为此，我们将标准的互补金属氧化物半导体（CMOS）相机转换为灵敏的检测器阵列，以探测在生物组织深处的弱光通量。具体来说，我们构建了一种基于CMOS的新颖，$〜20$ 同时在散粒噪声极限附近散斑，本质上起着 $〜20$独立的光子计数通道。我们基于MMF模式场解和检测器几何形状，开发出一种矩阵形式主义，以预测iDWS中的相干性和散斑数。在液体体模中验证后，我们在体内成人成年人脑中以2.5 cm源-检测器间距展示了iDWS搏动性血流测量结果。通过使用CMOS相机实现相干光波动的高度灵敏和并行测量，这项工作有望提高性能并降低漫射光学仪器的成本。