Laser-induced damage of dielectric-enhanced surface-modified single-point-diamond-turned Al-6061 multiband mirrors

Laser-induced damage threshold (LIDT) tests were performed at 1064 nm and 20 ns. Nodule defects were identified as the LIDT-limiting factor. The results suggest that the scale of the nodules is associated with the size of defects residing on the aluminum substrate surface. 3D finite-difference time-domain (FDTD) simulation was employed to calculate the electric field intensity (EFI) enhancement at the nodular defects with a seed diameter ranging from 0.35 μm to 2.5 μm. A direct linkage between the EFI enhancement and laser-induced damage morphology was established. Additional LIDT tests were conducted on surface modified aluminum substrate by using Corning aluminum process (CAP). The surface modification led to a 10x increase of the LIDT. Finally, LIDT of the multiband mirrors was predicted based on the absorption-driven damage and defect-driven damage. The results suggested that a combination of the CAP-modified Al6061 and low defect deposition process of the dielectric enhanced layers lead to high laser durability.