Abstract
Owing to their relatively high resistance to laser-induced damage, hafnia and silica are commonly used in multilayered optical coatings in high-power laser facilities as high- and low-refractive-index materials, respectively. Here, we quantify the laser-induced-damage threshold (LIDT) at 1053 nm in the short-pulse regime of hafnia and silica monolayers deposited by different fabrication methods, including electron-beam evaporation, plasma ion-assisted deposition and ion-assisted deposition. The results demonstrate that nominally identical coatings fabricated by different deposition techniques and/or vendors can exhibit significantly different damage thresholds. A correlation of the LIDT performance of each material with its corresponding absorption edge is investigated. Our analysis indicates a weak correlation between intrinsic LIDT and the optical gap of each material (Tauc gap) but a much better correlation when considering the spectral characteristics in the Urbach tail spectral range. Spectrophotometry and photothermal absorption were used to provide evidence of the correlation between the strength of the red-shifted absorption tail and reduced LIDT at 1053 nm.
Highlights
The past decades have seen the construction of petawatt-class laser facilities [1] such as FIREX [2], OMEGA EP [3], and Petal [4,5]
We observe a different trend for the layers coated by ion-assisted e-beam deposition (IAD) by vendor 1 for which the hafnia optical gap energy is the lowest for hafnia but the silica optical gap is in the range of other silica optical gaps
In this work we investigated the role of the deposition method for both silica and hafnia layers and their corresponding absorption edge spectral characteristics on the laser-induced-damage threshold (LIDT) of the asfabricated materials (LIDTint)
Summary
The past decades have seen the construction of petawatt-class laser facilities [1] such as FIREX [2], OMEGA EP [3], and Petal [4,5]. To understand the origin of laser damage in MLD-coated optics in the shortpulse regime, one needs to consider the difference between the damage threshold of the tested optic and the damage threshold of the constituent materials involved. This is because the intensity of the electric field within each layer varies significantly, depending on the design of the multilayer, giving rise to a distribution of enhanced electric-field intensity within each layer structure [7,8,9].
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