Speckle fluctuations in time-domain diffuse optics

Time-domain diffuse optics exploits near infrared light pulses diffused in turbid samples to retrieve their optical properties e.g., absorption and reduced scattering coefficients. Typically, interference effect are discarded, but speckle effects are exploited in other techniques e.g., diffuse correlation spectroscopy (DCS) to retrieve information regarding the tissue dynamics. Here, using a highly coherent Ti:Sapphire mode-locked laser and a single-mode detection fiber, we report the direct observation of temporal fluctuations in the measured distribution of time-of-flights (DTOF) curve. We study the dependence of these fluctuations on the sample dynamical properties (moving from fluid to rigid tissue-mimicking phantoms) and on the area of the detection fiber, which is directly linked to the number of collected coherence areas. Our observation agree with a time-resolved speckle pattern, and may enable the simultaneous monitoring of the tissue optical and dynamical properties.