Reducing the Stress of Hafnia/Silica Multilayers with Ion Assisted Deposition for Use in High-Power Diffraction Gratings

Proceedings of the 48th Annual Technical Conference of the Society of Vacuum Coaters (Society of Vacuum Coaters, 2005), pp. 421–425.

Authors:  D.J. Smith, C.M. Smith, and D. Hillier

Multilayer dielectric optical films are used to achieve high laser-induced damage threshold coatings for mirrors in high energy lasers. These coatings, usually made without ion-assisted deposition (IAD), can have low stress in a typical laboratory atmosphere on any substrate material. However, some applications, such as the generation of time-compressed pulses require a vacuum environment for propagation of the laser pulse. In these applications, films on low thermal expansion substrates develop excessive tensile stress. Ion-assist using an RF ion source is used to increase the compressive stress in the multilayers to achieve a low stress, high laser damage threshold multilayer coating on a silica substrate in vacuum. These coatings are suitable for use in an alldielectric diffraction grating (MLD).

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