Abstract
The physical mechanisms and ensuing material modification associated with laser-induced damage in multilayer dielectric high reflectors is investigated for pulses between 0.6 and 100 ps. We explore low-loss multilayer dielectric SiO2/HfO2 mirrors which are commonly employed in petawatt-class laser systems. The spatial features of damage sites are precisely characterized, enabling the direct correlation of the observed damage morphology to the location of energy deposition and the corresponding standing-wave electric-field intensities within the layer structure. The results suggest that there are three discrete damage-initiation morphologies arising from distinctly different mechanisms: the first prevailing at laser pulse lengths shorter than about 2.3 ps, while the other two are observed for longer pulses. Modeling of the thermomechanical response of the material to localized laser-energy deposition was performed for each type of damage morphology to better understand the underlying mechanisms of energy deposition and subsequent material response.
Highlights
The capability of multilayer dielectric (MLD) mirrors to transport ultrahigh-intensity laser pulses is limited by laser-induced damage that is associated with the localized formation of a plasma accompanied by high temperatures and pressures
Damage sites are typically created on the surface of the optic and are smaller than the size of the laser beam impinging on the optic, with their size related to the size of the damage-initiating defect and the duration of the laser pulse
We explore low-loss multilayer dielectric SiO2/HfO2 mirrors that are typically employed in petawatt-class laser systems operating at high peak intensity and energy per pulse in order to study laser–matter interactions in extreme conditions
Summary
The capability of multilayer dielectric (MLD) mirrors to transport ultrahigh-intensity laser pulses is limited by laser-induced damage that is associated with the localized formation of a plasma accompanied by high temperatures and pressures. We investigate the mechanisms of laser-induced damage on low-loss MLD SiO2/HfO2 mirrors with well-understood standing-wave electric-field intensities within the layer structure. Morphology of the damage sites provides evidence of the subsequent material relaxation This enables one to accurately determine the location of energy deposition and, with lesser accuracy, the thermodynamic pathway of material relaxation. The mechanism involved for intermediate pulse durations (between about 1 and 100 ps) remains inadequately understood, especially for complex optical structures such as MLD’s Such structures involve more than one material (typically alternating high- and low-refractive-index layers within the MLD stack), while damage can initiate within the different layers. We explore low-loss multilayer dielectric SiO2/HfO2 mirrors that are typically employed in petawatt-class laser systems operating at high peak intensity and energy per pulse in order to study laser–matter interactions in extreme conditions
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