measurementsnearinfraredis

Measurements near infrared refers to data collection in the near-infrared portion of the electromagnetic spectrum, approximately 780 to 2500 nanometers. This region lies just beyond the visible range and is governed by molecular overtone and combination vibrational absorptions, as well as relatively high penetration through some materials and tissues. The properties of near-infrared light make it useful for spectroscopy, imaging, and sensing in chemistry, biology, medicine, agriculture, and industry.

Measurement modalities include near-infrared spectroscopy (NIRS) for chemical analysis, diffuse reflectance and transmittance measurements, and near-infrared imaging such as functional near-infrared spectroscopy (fNIRS) for oxygenation and hemodynamics. Techniques span continuous-wave, time-domain, and frequency-domain approaches; choices affect depth sensitivity, information content, and instrumentation.

Instrumentation typically combines red- or near-infrared light sources such as LEDs and laser diodes with detectors like InGaAs photodiodes or arrays, often operated from 800 to 1700 nm, with expanded versions reaching about 2500 nm. Optical delivery and collection are commonly fiber-based or free-space, and calibration relies on reference materials or phantoms. For imaging, cameras based on InGaAs can provide two- or three-dimensional maps of absorption or scattering.

Applications include medical diagnostics and monitoring (for example, cerebral and muscle oxygenation), agricultural and food quality assessment, pharmaceutical and polymer analysis, and remote sensing. Limitations include strong water absorption bands near 1450 and 1950 nm, scattering in turbid media, and the need for robust calibration models and correction for atmospheric effects in airborne or satellite measurements.

See also: Near-infrared spectroscopy; diffuse optical tomography; functional near-infrared spectroscopy.