We have investigated the properties of magnesium fluoride films made using ion assisted deposition, with argon or Freon as the source gas. The effect of the ion species and residual gases on the chemical, physical, and optical properties have been determined. For all films, the optical performance is strongly depen-dent on the presence of residual oxygen-bearing gases. For the Freon bombarded films the incorporation of carbon is not seen to degrade their transparency, and a more stoichiometric Mg:F ratio is acheived.
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