Abstract
A principal possibility to overcome fundamental (intrinsic) limit of pure optical materials laser light resistance is investigated by designing artificial materials with desired optical properties. We explore the suitability of high band-gap ultra-low refractive index material (n less than 1.38 at 550 nm) in the context of highly reflective coatings with enhanced optical resistance. The new generation all-silica (porous/nonporous) SiO2 thin film mirror with 99% reflectivity was prepared by glancing angle deposition (GLAD). Its damage performance was directly compared with state of the art hafnia/silica coating produced by Ion-Beam-Sputtering. Laser-Induced Damage Thresholds (LIDT) of both coatings were measured in nanosecond regime at 355 nm wavelength. Novel approach indicates the potential for coating to withstand laser fluence of at least 65 J/cm2 without reaching intrinsic threshold value. Reported concept can be expanded to virtually any design thus opening a new way of next generation thin film production well suited for high power laser applications.
Highlights
Laser-induced damage (LID) phenomena is a principal limitation preventing achieval of higher optical power in almost every modern laser facility
HfO2 deposited by Ion Beam Sputtering (IBS) is considered as the reference high refractive index layer material in standard quarter-stack based high reflectivity mirror
In the case of GLancing Angle Deposition method (GLAD), different refractive indexes of silica single-layers were evaluated for two evaporation angles
Summary
Laser-induced damage (LID) phenomena is a principal limitation preventing achieval of higher optical power in almost every modern laser facility. Various production defects have been identified as damage precursors that trigger the extrinsic LID at low fluence Such defects can originate in any production step: starting from material synthesis and surface preparation[8] or later introduced by deposition technology[9]. It is possible to maintain appropriate spectral performance by shifting maximum peaks of the electric field towards more laser resistant layers[20, 21] or by inserting layers with intermediate refractive index[22]. Electric field optimization, and natural material choice limits will be exhausted, fundamental - intrinsic laser damage resistance limit will be reached. The objective of this research was to determine whether such coating design in combination of the low refractive index - high bandgap material has a potential that could lead to conceptually novel route how laser components for high power facilities are engineered. Optical and structural properties of the produced experimental mirror are characterized and directly compared with a similar multilayer coating, produced by state of the art Ion Beam Sputtering (IBS) technology and consisting of classical HfO2 and SiO2 layer design
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