The 2023 Laser Damage conference thin-film damage competition was devoted to a survey on the state-of-the-art broadband near-IR multilayer dielectric (MLD) mirrors designed for ultra-short pulsed laser applications. The requirements for the coatings were a minimum reflection of 99.5% at 45-deg incidence angle for S-polarization from 830 nm to 1010 nm and group delay dispersion (GDD) <±50 fs2. The participants were allowed to select the coating materials, coating design, and coating deposition method. Samples were damage tested at a single testing facility to enable direct comparison among the participants using a 25±5 fs optical parametric chirped-pulse amplification (OPCPA) laser system operating at 5 Hz. The testing results from this set of 37 samples showed that dense coatings by ion-beam sputtering (IBS), magnetron sputtering (MS), and electron-beam ion assisted deposition (e-beam IAD) exhibited highest damage initiation onset (laser-induced damage threshold or LIDT) while e-beam coatings were low performers. In addition, multilayer coatings using tantala and/or hafnia as high index materials were top performers. Furthermore, this competition included for the first time the measurement of the damage growth onset (laser-induced damage growth threshold or LDGT). This latter performance metric plays an important role in establishing the safe operational conditions for larger aperture ultrashort pulsed lasers. Information pertaining to the morphology of the damage sites and their evolution under subsequent exposure to different laser fluences leading to damage growth is presented. Finally, not all coating samples in the survey met the GDD requirements stated above and associated measurements are discussed in the context of the present and past thin-film damage competitions focused on similar broadband near-IR MLD coatings.

We show that the large-scale routine use of the fused silica debris shield (FSDS) maintains the ∼100× reduction in damage initiation rate and 70% increase in the install lifetime of a new grating debris shield (GDS) observed during pilot operations. Furthermore, we show that the install lifetimes of recycled GDS optics are nearly tripled using additional mitigation strategies such as expanding mitigation processing to include all damage sites larger than 10 μm (LT10) rather than just larger than 50 μm (LT50) and FSDS. We note that there is still a 50% difference between new and recycled optic installation lifetimes. We show that recycled optics have a 3.5× higher apparent initiation rate than new optics when exposed to nominally identical laser conditions.

Conventional manufacturing technologies, such as milling or casting, often reach their limits when complex geometries are involved. Additive manufacturing (AM) is a reasonable alternative for the fabrication of such parts. In particular, the powder bed fusion of metals using a laser beam (PBF-LB/M) has already been established in industrial production because it allows for the manufacturing of parts with high mechanical properties and a fine resolution. However, due to an uneven heat input during the process, the parts being manufactured are prone to thermally driven stress-induced cracking. We introduced an approach to predict regions within PBF-LB/M-manufactured parts that exhibit a high susceptibility to stress-induced fracture by means of numerical simulation. Previously identified and calibrated failure models for Inconel 718 were integrated into a PBF-LB/M process simulation, which uses the finite element method. Based on an implemented damage indicator, for which the failure models served as an input, critical locations due to the successive build-up of mechanical stresses and strains during layer-wise manufacturing were identified. The determined regions were experimentally validated by comparing the experimental results to the simulative predictions. An AM-adapted calibration approach allowed for a reliable prediction of crack-prone regions within PBF-LB/M-manufactured parts. An experimental method underestimated the susceptibility to failure, whereas a combined experimental and simulative approach overestimated it. The obtained results of this study contribute to the concept of first-time-right manufacturing as critical regions can be modified before the actual manufacturing process. The presented approach is also anticipated to be applicable to predicting crack formation between a solid part and its support structure.

We applied spatially shaped ultra-short pulses for laser micro-machining on the SiNx/c-Si layer system for the investigation of the selectivity ablation behavior of the sub-micrometer-thick SiNx top layer. In comparison to Gaussian beams, intensity spatially shaped pulses have the potential to minimize the superfluous energy in the peak region over the ablation threshold fluence as well as a steeper intensity drop at the side edge of the pulses. This can lead to more precise lateral and vertical ablation properties of the top thin film layer and lower modification or damage to the silicon substrate and the adjacent region. We compare the ablation variations due to beam shaping via light microscopic measurements on the micrometer-laser spot structures as well as the crystalline phases and stress modification via μm-Raman in the ablated spot, adjacent modified regions, and untreated reference areas. We focus on the design and fabrication of silicon membranes as advanced filters with a particular emphasis on controlling pore size and inter-pore distances to optimize filtration performance.

The National Ignition Facility (NIF) is intentionally operated with the final fused silica glass (SiO2) optics exposed to fluences and intensities with the potential to induce damage that will grow with additional laser exposure. Therefore, the NIF operates a recycle loop to refurbish final optics by mitigating any initiated surface damage to arrest its growth. However, the morphology of filamentary damage, caused by local self-focusing in the bulk of a silica optic, adds complexity to optics mitigation and provides a limitation to optic reusability. We evaluate techniques for mitigating isolated and clustered filamentary damage. Optical microscopy before and after installation on NIF was used to determine the efficacy of filamentary mitigation after a series of high fluence and intensity laser exposures. The challenges and success rate of the methods are compared for various filamentary damage mitigation strategies.