Continuous wave spectroscopy

Definition: Continuous wave (CW) spectroscopy is an fNIRS technique in which light of constant intensity is injected into tissue, and then the attenuated light signal is measured at a distance from the light source. Note, in practice all sources are switched off/on on some timescale; when the on/off time is long compared to relaxation/equilibrium in the sample, then such sources are considered to be continuous from the physics point of view.

Alternative definition: A technique that involves sending near-infrared light at a constant intensity into the tissue and measuring only the intensity of the re-emerging (i.e., diffusely reflected or transmitted) light.

Synonym: continuous-wave spectroscopy

References: T. Jue and K. Masuda. Application of Near Infrared Spectroscopy in Biomedicine. Handbook of Modern Biophysics. Springer US, 2013.

Related terms: Frequency Domain Spectroscopy, Time Domain fNIRS