Abstract
We propose a laser speckle based scheme that allows the analysis of local scattering properties of light diffusely reflected from turbid media. This turbid medium can be a soft material such as a colloidal or polymeric material but can also be biological tissue. The method provides a 2D map of the scattering properties of a complex, multiple scattering medium by recording a single image. We demonstrate that the measured speckle contrast can be directly related to the local transport mean free path l* or the reduced scattering coefficient μt = 1/l* of the medium. In comparison to some other approaches, the method does not require scanning (of a laser beam, detector or the sample itself) in order to generate a spatial map. It can conveniently be applied in a reflection geometry and provides a single characteristic value at any given position with an intrinsic resolution typically on the order of 5-50 μm. The actual resolution is however limited by the transport mean free path itself and can thus range from microns to millimeters.
Highlights
The determination of a sample’s optical scattering properties is important for a diverse set of fundamental research areas and industrial applications ranging from stability monitoring of complex fluids and formulations [1,2,3] to in-vivo biological studies of tissue composition and blood perfusion [4,5,6,7,8]
We propose a laser speckle based scheme that allows the analysis of local scattering properties of light diffusely reflected from turbid media
We demonstrate that the measured speckle contrast can be directly related to the local transport mean free path l∗ or the reduced scattering coefficient μt = 1/l∗ of the medium
Summary
The determination of a sample’s optical scattering properties is important for a diverse set of fundamental research areas and industrial applications ranging from stability monitoring of complex fluids and formulations (for example to differentiate sedimentation, creaming, phase separation) [1,2,3] to in-vivo biological studies of tissue composition and blood perfusion [4,5,6,7,8]. A number of techniques exist which provide a single measurement of the scattering properties of a given sample volume. Diffusing Wave Spectroscopy (DWS) [9] (or “Diffuse Transmission Spectroscopy” [10]) and coherent backscattering [11] are such techniques that can measure the scattering strength of a diffusive medium through determination of a characteristic parameter known as the transport mean free path l∗ or the reduced scattering coefficient μt = 1/l∗. Light reflected from a turbid medium has typically entered the object up to a depth z of a (few times the) transport mean free path l∗. In this article we describe a scheme that provides a 2D map of the diffuse scattering properties of a complex, multiple scattering medium by recording a single image with an exposure time in the milisecond range
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