Plasma-assisted deposition of metal fluoride coatings and modeling the extinction coefficient of as-deposited single layers

Abstract

We realized metal fluoride coatings with a high packing density and a low extinction coefficient by plasma (ion)-assisted deposition. The densification can be performed by different types of plasma sources, e.g., by a Leybold LION source and a Leybold APSpro, respectively. But the as-deposited coatings show a characteristic absorption behavior, whereas the absorption losses can be reduced in a postdeposition UV treatment step. We show experimental results of the plasma-assisted metal fluorides before and after the UV treatment and present a new model that allows us to describe and calculate the characteristic absorption losses of LaF3, MgF2, and AlF3.

Relation of optical properties and femtosecond laser damage resistance for Al2O3/AlF3 and Al2O3/SiO2 composite coatings

“…A reduction of optical losses by ex-situ UV irradiation has been reported for ion-assisted fluoride coatings in [10]. The ex-situ UV treatment in this study is realized by applying a xenon light source emitting at 172 nm in wavelength.…”

“…This increases the demand for UV coatings with the lowest optical losses, enhanced mechanical and environmental stability, and the highest laser damage resistance and pushes the development of coating technology. In the last two decades, the optical and microstructural properties as well as the laserinduced damage threshold (LIDT) of fluoride UV coatings fabricated by different deposition techniques have been the subject of several publications [1][2][3][4][5][6][7][8][9][10]. Although the deposition of mixture coatings with adjustable refractive indices, optical band gap energies, and laser damage resistance has been demonstrated for many oxide material combinations [11][12][13][14], oxyfluoride or fluoride composite coatings are rarely investigated [15][16][17][18][19].…”

Tailoring optical and non-optical properties of interference coating materials through the explicit use of small-scale optical inhomogeneities

“…Its optical behavior can be described by an effective dielectric function or a pair of effective optical constants, which appear to be a possibly complicated function of the optical constants of the constituents, their volume fractions, and morphology in the mixture [8,9] . These effective optical constants can therefore be tailored to a behavior that is not observed in any known pure material, but might be close to what is required in a particular application.…”

“…Application to a thin fi lm characterization task: locally understoichiometric fl uoride coatings As mentioned in Section 1, fl uctuations in the layer stoichiometry may lead to signifi cant absorption losses in coatings which are expected to be rather transparent when taking the average stoichiometry into account only. An extreme example is provided by fl uoride layers deposited by a plasma ion assisted electron beam evaporation technique (PIAD) [9,43] . Well stoichiometric lanthanum or magnesium fl uoride layers are transparent down to deep ultraviolet wavelength values.…”

“…Concerning the mentioned PIAD technique, as-deposited fl uoride layers show rather strong absorption losses, which can be reduced after deposition by a suitable post-treatment, exposing the layers to UV irradiation [9] . After having tested different physical mechanisms with respect to their ability to explain the measured absorption in a quantitative manner, a consistent mechanism could be identifi ed regarding the absorption losses as being caused by locally occurring understoichiometric areas in the fl uoride coating.…”