What Is fNIRS?
Functional near-infrared spectroscopy (fNIRS) is a neuroimaging technique using infrared laser light to measure brain activity. Light absorption/reflection patterns indicate where oxygenated blood concentrates, inferring active brain regions. fNIRS has been experimentally tried for deception detection — it is more portable and less expensive than fMRI but remains at an early research stage.
References
See: Butta et al. (2015); Li et al. (2018).