vuv

Vacuum ultraviolet (VUV) refers to the portion of the electromagnetic spectrum with wavelengths roughly from 100 to 200 nanometers, though some definitions extend toward the low end of the soft X-ray region. In this range, air strongly absorbs UV light and many common optical materials are opaque, so VUV work is conducted under vacuum or in inert gas environments. This imposes special requirements on light sources, optics, and detectors.

Optical components used for VUV must transmit or reflect in the vacuum and are made from materials with good VUV transmission, such as magnesium fluoride (MgF2) or lithium fluoride (LiF). Optics often employ specialized coatings for high reflectivity in the VUV. Detectors include cesium iodide (CsI) or cesium telluride (CsTe) photocathodes and microchannel plate assemblies. Light sources range from gas discharge lamps and hollow-cathode lamps to synchrotron radiation, with nonlinear processes such as high-harmonic generation enabling tunable VUV wavelengths. Because the medium is highly ionizing and readily absorbs photons, beamlines and samples are maintained under vacuum to minimize attenuation and contamination.

Applications of VUV techniques include spectroscopy and photoemission studies of surfaces and thin films, photochemistry, and atmospheric and solar physics. The high photon energy of VUV photons allows direct photoionization and electronic-structure measurements. Historically, shorter-wavelength UV played a role in photolithography and materials analysis, though modern deep-UV and EUV technologies now cover related but distinct wavelength ranges.

See also ultraviolet, extreme ultraviolet, photoemission spectroscopy, and photochemistry.