Kavli Affiliate: Changhuei Yang
| First 5 Authors: Jian Xu, Ali K. Jahromi, Changhuei Yang, ,
| Summary:
Diffusing wave spectroscopy (DWS) is a well-known set of methods to measure
the temporal dynamics of dynamic samples. In DWS, dynamic samples scatter the
incident coherent light, and the information of the temporal dynamics is
encoded in the scattered light. To record and analyze the light signal, there
exist two types of methods – temporal sampling methods and speckle ensemble
methods. Temporal sampling methods, including diffuse correlation spectroscopy
(DCS), use one or multiple large bandwidth detectors to well sample and analyze
the temporal light signal to infer the sample temporal dynamics. Speckle
ensemble methods, including speckle visibility spectroscopy (SVS), use a
high-pixel-count camera sensor to capture a speckle pattern and use the speckle
contrast to infer sample temporal dynamics. In this paper, we theoretically and
experimentally demonstrate that the decorrelation time ({tau}) measurement
accuracy or SNR of the two types of methods has a unified and similar
fundamental expression based on the number of independent observables (NIO) and
the photon flux. Given a time measurement duration, NIO in temporal sampling
methods is constrained by the measurement duration, while speckle ensemble
methods can outperform by using simultaneous sampling channels to scale up NIO
significantly. In the case of optical brain monitoring, the interplay of these
factors favors speckle ensemble methods. We illustrate that this important
engineering consideration is consistent with the previous research on blood
pulsatile flow measurements, where a speckle ensemble method operating at
100-fold lower photon flux than a conventional temporal sampling system can
achieve a comparable SNR.
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