Near infrared light pulses, multiply scattered by random media, carry useful information regarding the sample key constituents and their microstructures. Usually, the photon diffusion equation is used to interpret the data, which neglects any interference effect in the detected light fields. However, in several experimental techniques, such as diffuse correlation spectroscopy or laser speckle flowmetry, the effect of light coherence is exploited to retrieve the information on the sample dynamical properties. Here, using an actively mode-locked Ti:Sapphire laser, we report the observation of temporal fluctuations in the diffused light pulse, which cannot be described by the diffusion theory. We demonstrate the sensitivity of these fluctuations on the sample dynamical properties and on the number of detected coherence areas (i.e., speckles). In addition, after interpreting the effect as a time-resolved speckle pattern, we propose a simple statistical method for its quantification. The proposed approach may enable the simultaneous monitoring of the static (absorption and scattering coefficients) and dynamical (Brownian diffusion coefficient) properties of the sample, and also provide physical insight on the propagation of optical waves in random media.

中文翻译：

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时域漫射光学中的相干波动

近红外光脉冲被随机介质所分散，携带有关样品关键成分及其微结构的有用信息。通常，光子扩散方程用于解释数据，而忽略了检测到的光场中的任何干涉效应。但是，在一些实验技术中，例如漫射相关光谱法或激光散斑流量计，利用光相干效应来获取有关样品动力学特性的信息。在这里，我们使用主动锁模的Ti：Sapphire激光器，报告了观察到的散射光脉冲的时间波动，这不能用散射理论来描述。我们证明了这些波动对样品动力学性质以及检测到的相干区域（即斑点）数量的敏感性。此外，在将效果解释为时间分辨的斑点图案后，我们提出了一种简单的统计方法对其进行量化。所提出的方法可以使得能够同时监测样品的静态（吸收和散射系数）和动态（布朗扩散系数）特性，并且还可以提供关于光波在随机介质中传播的物理信息。