Rear-Face Reflective Coating for VUV Optical Elements
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Solution Overview
Problem
Reflective coatings for the vacuum ultraviolet (VUV) wavelength range are prone to degradation due to oxidation and chemical alteration under high irradiation, leading to reduced reflectance and increased scattered light, especially when exposed to ambient conditions with higher oxygen or water content.
Innovation Solution
An optical element design featuring a reflective coating applied to the rear face of a transparent substrate, with a protective coating applied to the side remote from the substrate, allowing for a thicker and more effective protective layer without the need for transparency in the VUV range, utilizing oxidic materials like Al2O3 and dielectric multilayer coatings to enhance reflectivity and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reflective coating is applied to the front face of the substrate, then the coating is exposed to radiation and environmental degradation, but the protective effect is reduced due to direct exposure to oxidation and chemical alteration
Solution Approach 1:
The reflective coating is inverted from the conventional front-face position to a rear-face position on the substrate. This inversion allows the protective coating to be applied to the front face where it is exposed to radiation, while the reflective coating remains on the rear face protected from direct environmental exposure. The optical path is modified so that radiation passes through the substrate to reach the reflective coating, eliminating direct exposure to harmful oxidation and chemical alteration while maintaining reflective functionality.
2Reliability
If a protective coating is applied to the front face for VUV radiation, then the coating must be transparent in the VUV range, but this limits the thickness and protective effectiveness
Solution Approach 1:
The protective coating is repositioned from the front face to the rear face of the substrate, away from the VUV radiation path. This allows the protective coating to be applied as a thicker layer without compromising VUV transparency, since it no longer needs to be transparent in the VUV range. The thicker protective coating can effectively block oxygen and water diffusion while the optical functionality is maintained through the substrate and reflective coating arrangement.
3Reliability
If the reflective coating is exposed to ambient conditions with higher oxygen or water content, then the coating degrades faster, but placing it in a protected position reduces accessibility to harmful environments
Solution Approach 1:
The reflective coating is positioned on the rear face of the substrate, physically separated from the ambient environment with higher oxygen or water content. This inverted configuration creates a protective barrier effect where the substrate acts as a barrier between the reflective coating and harmful environmental factors. The reflective coating is no longer directly exposed to oxidation and chemical alteration, significantly improving its stability and reducing degradation rates while maintaining optical performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly improves the protective effect of the coating, maintaining high reflectance and reducing degradation, even under high irradiation conditions, by isolating the reflective coating from the protective coating and using dense oxidic layers to prevent oxygen and water diffusion.
Implementation Method 1
a reflective coating, applied to the substrate, for reflection of radiation in a first wavelength range between 100 nm and 700 nm
Implementation Method 2
a protective coating applied to the reflective coating, in particular for protection of the reflective coating from oxidation
Data Source
AI summary
An optical element includes: a substrate, a reflective coating, applied to the substrate, for reflecting radiation in a first wavelength range (Δλ1) between 100 nm and 700 nm, preferably between 100 nm and 300 nm, more preferably between 100 nm and 200 nm, and a protective coating applied to the reflective coating. The substrate is formed from a material which is transparent to the radiation in the first wavelength range (Δλ1). The reflective coating is applied to a rear face of the substrate and is structured to reflect radiation that passes through the substrate to the reflective coating. Also disclosed are an optical arrangement with at least one such optical element and a method of producing such an optical element.