Decrease of nanosecond LIDT of UV-optics under large incident angle
SPIE Optical Systems Design
14. Mai
Frankfurt am Main
2018
Type: Konferenzbeitrag
Abstract
Further improvements in laser resistance of optics to meet the requirements of the advancing high-power lasers for the UV-spectral region could be achieved by careful control of the electric field intensity (EFI) in the layer system. In theory, it is possible to reduce the EFI in high reflecting optics for s-polarized radiation by the use of large angles of incidence and thus increasing the LIDT of the optic. In order to experimentally proof this theory, two coating designs for different AOI were prepared. A set of high reflecting mirrors was fabricated by means of electron-beam evaporation and tested by 1-on-1 LIDT measurements for multiple beam diameters. The prediction of a higher LIDT for an AOI of 65 ° was verified for small beam diameters. However, for large beam diameters a decrease of LIDT was observed. To investigate the cause of this behavior, which could be explained by the influence of a defect density inside the coating, a second set of samples was produced with 10 nm gold nanoparticles embedded at the interface with the highest EFI. Damage testing of these samples showed a decrease of the absolute values of the LIDT but also reproduced the abnormal behavior in LIDT for an oblique angle of incidence and large beam diameters. Analysis of the damage morphology indicated that the damage behavior is independent of the defect distribution in the sample. Influences of the coating process on the observed damage behavior were studied with a third set of samples prepared by ion beam sputtering (IBS).