Understanding the physical mechanism behind the laser-induced damage of multilayer dielectric interference coatings is essential for developing ultra-high intensity laser systems. The previous work reported high damage thresholds of MLD mirrors and blister formation near the threshold. Here, we present the cross-sectional study of the blisters using transmission electron microscopy and focused ion-beam processing. The measurement shows evidence of void formation and phase transformation under the surface, interdiffusion, and intermixing at the interfaces. These findings provide valuable insights into the mechanisms behind laser-induced damage, facilitating the development of more robust and reliable optics for high-power laser applications.
Understanding the physical process behind laser-induced damage of multilayer dielectric (MLD) interference coatings (IC) is of supreme importance for building ultrahigh-intensity laser systems. We experimentally studied the S-on-1 laser-induced damage threshold (LIDT) and damage characteristics of the SiO2/HfO2 high reflector quarter-wave stacks for three different femtosecond pulse durations operating at 1030nm wavelength. The S-on-1 LIDT for 1,10,100,1000 and 10000 pulses were recorded, and the values compare well with the state of the art. A strong correlation between single-shot damage morphology and laser focal intensity profiles was observed. Potential damage mechanisms of IC layers consistent with our observation will be discussed.
The pulse compression grating (PCG) is one of the most critical components of a high power chirped pulse amplification laser system to achieve the shortest pulse duration. Compared to metal gratings, a multi-layer dielectric (MLD) grating is a possible solution to improve the laser induced damage threshold (LIDT) of PCGs. Our previous work reported simulations of electron excitation dynamics in the interaction of MLD mirrors and femtosecond pulses (<100 fs). Here we present the study of the interaction of a MLD grating and a 50-fs pulse using a 2D dynamic simulation modeling both the E-field enhancement and transient material responses.
The interaction of ultrafast laser pulses and dielectric materials has been under intensive research for improvement of laser induced damage of optics for high intensity lasers. A 2D model based on Keldysh photoionization and finite-different time-domain (FDTD) algorithm are used to simulate the ionization processes in multilayer interference coatings, taking nonlinear photoionization, impact ionization, and plasma collision into account. Simulation and experimental results of bulk fused silica with different pulse durations and angles of incidence are compared and discussed. We also simulated the interaction of a 40-layer SiO2/Ta2O5 high reflective interference coating designed for 45° angle of incidence and a p-polarized 5-fs pulse at a wavelength of 800 nm, and the damage threshold of the coating is estimated.
In this work we report an experimental investigation of subsurface damage (SSD) in conventionally polished fused silica (FS), sapphire substrates, and YAG crystals which are widely used in laser applications and directly influence performances of critical ultrahigh intensity and high average power laser system optics.
Two surface treatment procedures were tested: 1 – plasma treatment, 2 – chemical treatment. Plasma and chemical treatments were applied to fused silica substrates. The laser induced damage threshold (LIDT) FS substrates were studied as the function of etching depth.
The pulse duration dependence of single-shot laser-induced damage and ablation of HfO2/SiO2-based double- and quadlayer thin films is studied using time-resolved surface microscopy (TRSM) and ex situ imaging down to the few-cycle pulse (FCP) regime. Both samples exhibit a raised, "blister" morphology for a range of fluences between the damage and ablation thresholds. The fluence range associated with blister formation is much larger for FCPs than for 110 fs pulses, and TRSM images at early time-delays show that the density of the laser-generated plasma is much higher for 110 fs pulses for a lower fluence relative to the damage threshold. Also, for high enough fluences the excited electron density exhibits a fast decay down to a significantly high value, which remains even after the onset of mechanical damage of the layers. The pulse duration dependence suggests that as fluence is increased, the increase in absorbed energy is more gradual for FCPs, which points towards inherent differences in the way high intensity FCPs are absorbed in dielectrics relative to longer femtosecond laser pulses.
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