Abstract
Growth of laser damage on High Reflection (HR) thin film coatings is investigated at the wavelength of 1.030µm in the sub-picosecond regime. An experimental laser damage setup in a pump / probe configuration is used to study the growth behavior of engineered damage sites as well as laser damage sites. Results demonstrate that engineered sites and laser damage sites grow identically which indicates that the growth phenomenon is intrinsic to materials and stack design. In order to analyze the experimental results, we have developed a numerical model to simulate growth. Using FEM simulations, we demonstrate that growth is governed by the evolution of the electric field distribution in the mirror stack under the successive laser shots, which is supported by time-resolved observations of damage growth events. Eventually the results are compared to laser damage observations made on of full scale PETAL mirrors, which fully support the approach.
Highlights
Laser-damage performance of reflective optics such as High Reflection (HR) mirrors or pulse compression gratings is the topic of important interest for large aperture ultra-high intensity laser Petawatt to multi-Petawatt facilities such as PETAL, OMEGA-EP, FIREX, or ELI [1,2,3,4,5]
Using FEM simulations, we demonstrate that growth is governed by the evolution of the electric field distribution in the mirror stack under the successive laser shots, which is supported by time-resolved observations of damage growth events
Efforts carried out currently by the short pulse community mostly use 1-on-1 or S-on-1 damage threshold protocols based on ISO standard [6] to quantify the damage resistance of these optical components
Summary
Laser-damage performance of reflective optics such as HR mirrors or pulse compression gratings is the topic of important interest for large aperture ultra-high intensity laser Petawatt to multi-Petawatt facilities such as PETAL, OMEGA-EP, FIREX, or ELI [1,2,3,4,5]. In the sub-picosecond regime, such a measurement protocol is useful to estimate intrinsic damage performances of a given material or mirror stack/grating design It gives a sparse view of the lifetime of meter scale optics during operation on a real laser system. Lifetime is limited by two different phenomena: damage initiation which represents the onset of damage for a given fluence on rare localized sites; and damage growth which is the tendency of damage to grow under iterative shots Facing this limitation, the community involved nanosecond laser damage at 351nm for facilities such as NIF [7] or LMJ [1] developed the raster scan testing protocol to estimate damage initiation on meter scale optics [8,9]. Damage growth was studied to be able to predict damage size after a shot sequence [10,11]; damage mitigation technics were proposed [12]
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