Laser-resistance sensitivity to substrate pit size of multilayer coatings

Abstract

Nanosecond laser-resistance to dielectric multilayer coatings on substrate pits was examined with respect to the electric-field (E-field) enhancement and mechanical properties. The laser-induced damage sensitivity to the shape of the substrate pits has not been directly investigated through experiments, thus preventing clear understanding of the damage mechanism of substrate pits. We performed a systematic and comparative study to reveal the effects of the E-field distributions and localized stress concentration on the damage behaviour of coatings on substrates with pits. To obtain reliable results, substrate pits with different geometries were fabricated using a 520-nm femtosecond laser-processing platform. By using the finite element method, the E-field distribution and localized stress of the pitted region were well simulated. The 1064-nm damage morphologies of the coated pit were directly compared with simulated E-field intensity profiles and stress distributions. To enable further understanding, a simplified geometrical model was established, and the damage mechanism was introduced.

Scratch Morphology Transformation: An Alternative Method of Scratch Processing on Optical Surface

“…Scratches significantly influence the nearby light field distribution and generate intensity enhancement. The enhancing extent is directly related to the scratch morphology [ 14 , 21 ]. Utilizing finite difference time domain (FDTD) simulation, we established a light field distribution model of the scratches in Section 2 .…”

Polarization Characteristics of the Near-Field Distribution of One-Dimensional Subwavelength Gratings

“…The field intensity distribution in and on the surface of optical elements has aroused great interest as one of the many factors that affect the anti-laser-induced damage performance of optical elements. The LIDT of optical elements can be further improved by optimizing the field intensity design [6]- [8]. Various subwavelength antireflective surfaces [9] inspired by the structure of biological eyes have been studied [10].…”

Multilayer deformation planarization by substrate pit suturing

“…For a rotating substrate in an EB evaporation coater, the multilayer dielectric coating growth exhibits a self-shadowing nature. Nodules originated from contamination and particle defects can be readily apparent on a given surface [8][9][10], but pit and scratch defects are typically buried under the coating layers and cannot be easily observed [11][12][13], especially on large-scale samples or hydrofluoric acid-etched substrate before deposition. Nodule defects could be recovered by a planarization coating process, utilizing the defect-smoothing technology principles originally developed for extreme ultraviolet lithography masks [14].…”

“…By a discrete process of angle-dependent ion etching and unidirectional ion-beam deposition, the planarization effect has been shown to increase the laser resistance of 1ω mirror coatings above 100 J • cm −2 . Substrate scratches and pits are also considered a primary damage source and have attracted the most research attention in recent years [11][12][13]. However, scratches and pits cannot be effectively eliminated by current planarization technologies.…”

“…We have previously investigated the negative impacts of the internal cracks on laser resistance in Ref. [13]. The substrate pit deformational effects during deposition could be isolated by a suture layer.…”