Glancing-angle–deposited magnesium oxide films for high-fluence applications

Birefringent magnesium oxide thin films are formed by glancing-angle deposition to perform as quarter-wave plates at a wavelength of 351 nm. These films are being developed to fabricate a large-aperture distributed-polarization rotator for use in vacuum, with an ultimate laser-damage-threshold goal of up to 12 J/cm super(2) for a 5-ns flat-in-time pulse. The laser-damage threshold, ease of deposition, and optical film properties are evaluated. While the measured large-area laser-damage threshold is limited to ~4 J/cm super(2) in vacuum, initial results based on small-spot testing in air (>20 J/cm super(2)) suggest MgO may be suitable with further process development.