Optical window

Definition: The optical window for biological tissues defines a range of wavelengths (650-900 nm) where light can penetrate through tissues such as skin and bone more efficiently than visible light because these tissues scatter and absorb less light at these wavelengths, rendering them nearly transparent. fNIRS takes advantage of this window, where water absorption is low and oxygenated and deoxygenated hemoglobin are strong absorbers of light at these wavelengths, with contrasting levels of absorption coefficient in this range.

Alternative definition:

Synonym: near-infrared window; therapeutic window

References:

https://doi.org/10.1038/nnano.2009.326

https://doi.org/10.1038/s41377-021-00628-0

Related terms: oxygenated hemoglobin, deoxygenated hemoglobin, absorption spectrum, absorption coefficient