Fluorine in optics

Fluorine occupies an original and strategic position in modern optics. The F2 excimer lasers are unrivaled sources of deep UV light for semiconductors, microphotolithography and micromachining which has brought on the development of single crystal calcium fluoride optics. Due to the weak polarisability of the fluoride ion, fluoride materials have low refractive index suitable for thin film antireflective coatings specially in IR optics. Transparent magnesium fluoride ceramics, prepared by fine grains hot pressing, are transparent in the mid IR where the transparency windows of the atmosphere are located. They are used as IR domes for missiles guidance. Fluoride glasses when elaborated as optical fibers or channel waveguides and when doped with appropriate lanthanides, are original optical devices for laser operations lying from the mid IR to the UV region where light emission is characterized by up-conversion phenomena. The same devices have also found industrial applications in telecommunications as a new generation of optical amplifiers operating in the ultra-transparency window of the silica fiber.