Optical Pathlength

Definition: In broader context, the term refers to the trajectory that the light follows within a medium. Path length is the distance obtained as the product of the propagation velocity and the propagation delay between two points. In the propagation of waves, path length is the length that is proportional to the time a wave or signal takes to travel from one point to another. Within the fNIRS (or optical imaging) framework, it refers to the trajectory that the emitted light follows from source to the detector within the tissue (e.g., scalp, brain, etc.). In tissue or brain imaging scattering is dominant and leads to many different trajectories. The path of light when measured from a source to a detector exhibits a banana-shaped curve and it is directly proportional to the physical length between the source and detector.

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References:

https://doi.org/10.1117%2F1.NPh.8.1.012101

Related terms: Differential Path length factor, Photon Banana