Systems and methods for path length selected diffuse correlation spectroscopy

A method for making a path length selected diffuse correlation spectroscopy (PLS-DCS) measurement of scattering particle dynamics within a target medium, the method comprising:

• a) coupling a PLS-DCS source and a PLS-DCS detector to the target medium, the PLS-DCS source configured to emit a first light having a first coherence length of less than a path length distribution of the target medium;
• b) selecting the first coherence length of the first light and/or a first path length of a first reference optical path to acquire a PLS-DCS measurement for a desired path length distribution of the target medium;
• c) transmitting a first portion the first light from the PLS-DCS source into the target medium and a second portion of the first light along the first reference optical path;
• d) combining at least a portion of the first portion of the first light after passing through the target medium and the second portion of the first light after passing along the first path length of the first reference optical path, thereby providing a combined optical signal;
• e) receiving the combined optical signal at the PLS-DCS detector, thereby generating a PLS-DCS detector signal including path length information and correlation information for the combined optical signal;
• f) determining, using a processor, the path length information, the correlation information, and one or more equations relating path length and correlation to dynamics, a dynamics of the target medium;
• and
• g) generating a report including the dynamics of the target medium.

A method of making a path length selected diffuse correlation spectroscopy (PLS-DCS) measurement of a target medium, the method comprising:

• a) coupling a PLS-DCS source and a PLS-DCS detector to a surface of the target medium;
• b) transmitting a first portion of a first light from the PLS-DCS source into the target medium and a second portion of the first light along a reference optical path, the first light having a first coherence length of less than a path length distribution of the target medium;
• c) interferometically detecting, using the PLS-DCS detector, at least a portion of the first portion of the first light after passing through the medium and the second portion of the first light after passing along a first path length of the reference optical path, thereby generating a first interferometric signal;
• d) repeating steps b) and c), substituting a second coherence length for the first coherence length and a second path length for the first path length, thereby generating a second interferometric signal in place of the first interferometric signal, wherein the second coherence length is different than the first coherence length or the second path length is different than the first path length;
• e) determining a first measured path length distribution based on the first coherence length and the first path length and a second measured path length distribution based on the second coherence length and the second path length;
• f) determining, using a longer distribution between the first measured path length distribution and the second measured path length distribution, an inner dynamics of an inner portion of the target medium relative to the surface, or, using a shorter distribution between the first measured path length distribution and the second measured path length distribution, a superficial dynamics of a superficial layer of the target medium relative to the surface;
• and
• g) generating a report including the inner dynamics or the superficial dynamics.