Unusual behavior has been reported for D2O/H2O-dosed CaF2 optical thin films. This behavior includes resistance to laser-induced damage at 2.7-μm radiation, improved damage morphology, and reduced optical absorption in the water band for even H2O-dosed CaF2 optical thin films. Analysis of the films strongly suggests that the modification of film properties is not the result of inclusion of the D2O/H2O into the film matrix or chemical contamination. Rather, the act of dosing has modified the structural properties of the films, thus producing the effects observed.