Opticalinfrared

Opticalinfrared refers to the collection of techniques and instruments that operate across the optical and infrared portions of the spectrum, from the near ultraviolet to the mid- or far-infrared. In practice, a common definition spans about 0.4 to 25 micrometers, with distinct subregions such as visible (≈0.4–0.7 μm), near-infrared (≈0.7–2.5 μm), and mid-infrared (≈2.5–25 μm).

Key technologies include detectors and cameras: silicon-based sensors for visible and part of near-IR; indium gallium arsenide (InGaAs) for 0.9–1.7 μm; indium antimonide (InSb) and mercury cadmium telluride (HgCdTe) for mid-IR, often operated at cryogenic temperatures. Optical components use materials such as CaF2, ZnSe, Ge, and chalcogenide glasses; coatings optimized for IR wavelengths. Imaging and spectroscopy rely on cooled systems to reduce thermal noise; adaptive optics improve resolution in ground-based telescopes. In astronomy and remote sensing, filters, spectrometers, and interferometers cover multiple bands.

Applications span astronomy (thermal emission and reflected light), remote sensing and earth observation, industrial inspection, and medical imaging and spectroscopy in the near- and mid-IR. Thermal imaging detects surface temperature distributions; infrared spectroscopy identifies chemical bonds; night-vision and surveillance rely on detectors sensitive in the near-IR to mid-IR range.

Challenges include variable atmospheric transmission dominated by water vapor; strong thermal emission from the environment and instruments requiring cooling; detector dark current and read noise; calibration across wide wavelength ranges. The field continues to evolve with advances in photonic components, detector materials, and computational methods for signal processing.