Thick HfO₂ single layers derived from a reactive plasma ion assisted deposition were investigated with a designed film thickness of 800 nm. The film structure was modeled by fitting the corresponding variable angle spectroscopic ellipsometric data and correlated to the ratio of plasma ion momentum transfer during the film deposition. Scatter loss was calculated according to a multilayer model as well as a single surface model. Water absorption in the MWIR was used to confirm the revealed film structure. The results indicate that the scatter loss of the HfO₂ based high reflective optics can be estimated by using a single surface model in a first-order approximation from the DUV to the MWIR. A linear relationship between the refractive index inhomogeneity and the amount of plasma ion momentum transfer during the deposition was established. The total loss at 2.95 μm is dominated by the absorptance loss, whereas both the absorptance and the scatter losses are reduced as the ratio of plasma ion momentum transfer increases. Appropriately optimizing and selecting deposition parameters enable low loss and environmentally stable HfO₂ coatings, leading to numerous defense applications from the DUV to the MWIR.

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Jue Wang, Michael J. Cangemi, Christopher J. Chinhong, Michael J. D'lallo, Jim E. Platten, Jean Francois Oudard, and Leonard Wamboldt, "Characterization of reactive plasma ion assisted HfO2 films for low loss optical coatings in the DUV and MWIR," Proc. SPIE 10181, Advanced Optics for Defense Applications: UV through LWIR II, 101810P (Presented at SPIE Defense + Security: April 10, 2017; Published: 11 May 2017); https://doi.org/10.1117/12.2271889.