Modelling analysis of influence of substrate surface defect on optical characteristics of single-layer coating

A simple and practical model is used to analyse the influence of substrate surface defect on the optical characteristics of a single-layer coating. A single-layer coating is prepared and its optical properties are fitted. Some explanations for the origin of the transition layer are presented. It is concluded that there is a transition layer forming between the substrate and coating, which is attributed to substrate surface defects, and its refractive index change is nearly of linearity.

负离子元素杂质破坏模型

探讨了HfO2薄膜中负离子元素杂质破坏模型，并得出薄膜中的杂质主要来源于镀膜材料。用电子束蒸发方法沉积两种不同Cl元素古量的HfO2薄膜，测定薄膜弱吸收和损伤阈值来验证负离子元素破坏模型。结果表明，随着Cl元素含量的增加薄膜的弱吸收增加损伤阈值减小。这主要是因为负离子元素在蒸发过程中形成挥发性的气源中心而产生缺陷，缺陷在激光辐照过程中又形成吸收中心．因此负离子元素的存在将加速薄膜的破坏。

斜角入射沉积法制备渐变折射率薄膜的折射率分析

斜角入射沉积法是一种制备薄膜的新颖方法，它可以用来制备渐变折射率薄膜．本文首先探讨了膜料的沉积入射角为α，薄膜柱状生长倾斜角为β时的薄膜的填充系数；之后利用drude理论，分析研究了斜角入射沉积法制备渐变折射率薄膜的折射率与薄膜的入射角和生长方向的关系．

Defect-induced failure of optical coating filters

Optical filters composed of Ag, Al2O3, and ZnSe films were prepared on BK7 substrates by evaporation. By employing spectrophotometer, microscope, scanning electron microscope (SEM), and energy dispersive spectrum (EDS) analysis, the moisture-dependent stability of the samples was tested. The experimental results revealed that filter failure often occurs initially at defect sites. Small sputtering particles and pinhole are found to be two types of defects that induced the optical coating filter failure. The mechanisms of the defect-induced failure of the filters also are discussed in the article. (C) 2005 Elsevier Ltd. All rights reserved.

薄膜材料对TiO2基薄膜激光损伤阈值的影响

abstract {The optical property, structure, surface properties (roughness and defect density) and laser-induced damage threshold (LIDT) of TiO₂ films deposited by electronic beam (EB) evaporation of TiO₂ (rutile), TiO₂ (anatase) and TiO₂ + Ta₂O₅ composite materials are comparatively studied. All films show the polycrystalline anatase TiO₂ structure. The loose sintering state and phase transformation during evaporating TiO₂ anatase slice lead to the high surface defect density, roughness and extinction coefficient, and low LIDT of films. The TiO₂ + Ta₂O₅ composite films have the lowest extinction coefficient and the highest LIDT among all samples investigated. Guidance of selecting materials for high LIDT laser mirrors is given.}

Optimization of thin-film design for multi-layer dielectric grating

Thin-film design used to fabricate multi-layer dielectric (MLD) gratings should provide high transmittance during holography exposure, high reflectance at use wavelength and sufficient manufacturing latitude of the grating design making the MLD grating achieve both high diffraction efficiency and low electric field enhancement. Based on a (HLL)H-9 design comprising of quarter-waves of high-index material and half-waves of low-index material, we obtain an optimum MLD coating meeting these requirements by inserting a matching layer being half a quarter-wave of Al2O3 between the initial design and an optimized HfO2 top layer. The optimized MLD coatings exhibits a low reflectance of 0.017% under photoresist at the exposure angle of 17.8 degrees for 413 nm light and a high reflectance of 99.61% under air at the use angle of 51.2 degrees for 1053 nm light. Numerical calculation of intensity distribution in the photoresist coated on the MLD film during exposure shows that standing-wave patterns are greatly minimized and thus simulation profile of photoresist gratings after development demonstrates smoother shapes with lower roughness. Furthermore, a MLD gratings with grooves etched into the top layer of this MLD coating provides a high diffraction efficiency of 99.5% and a low electric field enhancement ratio of 1.53. This thin-film design shows perfect performances and can be easily fabricated by e-beam evaporation. (c) 2006 Elsevier B.V. All rights reserved.

Influence of ZrO2 in HfO2 on reflectance of HfO2/SiO2 multilayer at 248 nm prepared by electron-beam evaporation

Influence of ZrO2 in HfO2 on the reflectance of HfO2/SiO2 multilayer at 248 nm was investigated. Two kinds of HfO2 with different ZrO2 content were chosen as high refractive index material and the same kind of SiO2 as low refractive index material to prepare the mirrors by electron-beam evaporation. The impurities in two kinds of HfO2 starting coating materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum (GDMS) technology and secondary ion mass spectrometry (SIMS) equipment, respectively. It showed that between the two kinds of HfO2, either the bulk materials or their corresponding films, the difference of ZrO2 was much larger than that of the other impurities such as Ti and Fe. It is the Zr element that affects the property of thin films. Both in theoretical and in experimental, the mirror prepared with the HfO2 starting material containing more Zr content has a lower reflectance. Because the extinction coefficient of zirconia is relatively high in UV region, it can be treated as one kind of absorbing defects to influence the optical property of the mirrors. (C) 2008 Elsevier B.V. All rights reserved.

Thermal-mechanical modeling of nodular defect embedded within multilayer coatings

The initiation of laser damage within optical coatings can be better understood by thermal-mechanical modeling of coating defects. The result of this modeling shows that a high-temperature rise and thermal stress can be seen just inside the nodular defect compared to surrounding coating layers. The temperature rise and thermal stress tend to increase with seed diameter. Shallower seed tend to cause higher temperature rise and greater thermal stress. There is a critical seed depth at which thermal stress is largest. The composition of the seed resulting from different coating-material emission during evaporation can affect the temperature rise and thermal stress distribution.