EUV

Extreme ultraviolet (EUV) refers to the portion of the electromagnetic spectrum with wavelengths roughly from 10 to 121 nanometers. EUV lies between the vacuum ultraviolet and soft X-ray regions and is strongly absorbed by air, so experiments and observations are conducted in vacuum or in controlled inert gas environments.

EUV photons have high energy and can easily photoionize most materials, causing rapid damage to optical surfaces. Conventional glass and many coatings are opaque at these wavelengths, so EUV systems rely on reflective optics rather than lenses. Typical EUV mirrors use multilayer coatings (for example alternating molybdenum and silicon layers) and are configured as grazing-incidence or near-normal incidence components tuned for specific bands around 13.5 nm or other wavelengths.

Industrially, the dominant application is extreme ultraviolet lithography (EUVL) for semiconductor manufacturing. The 13.5 nm band is generated by laser-produced plasma sources (often tin microdroplets) and requires a complex vacuum environment and high-precision reflective optics. ASML currently leads the market for commercial EUV lithography systems. In addition, EUV imaging and spectroscopy are used in solar physics and high-temperature plasma research, employing space-based telescopes and instruments.

Key challenges include achieving sufficient photon flux, preserving mirror reflectivity in a harsh vacuum, preventing contamination and surface degradation, and producing defect-free masks. The technology demands extensive vacuum systems, advanced metrology, and substantial operating costs. Safety considerations are also important due to high-energy photons and ionizing radiation.

Beyond lithography, EUV studies contribute to understanding hot astrophysical plasmas, enabling observations of the Sun's corona and other energetic sources.