Dielectric Mirror Coating for UV Etalons
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Solution Overview
Problem
Dielectric mirrors used in etalons for ultraviolet radiation applications face challenges in achieving high reflectivity while maintaining sufficient transmission and minimizing stress-induced cracking, which affects the accuracy of interferometric measurements.
Innovation Solution
A mirror with a dielectric coating comprising two layer stacks: a first stack of alternating high and low refractive index oxides, and a second stack of alternating fluorides and oxides, with a limited proportion of fluoride layers to ensure high reflectivity and transmission, and a substrate made of quartz glass to minimize stress and enhance durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a dielectric coating with high proportion of fluoride layers is used to achieve high reflectivity, then reflectivity is improved, but transmission decreases and stress-induced cracking increases
Solution Approach 1:
The patent changes the proportion parameter of fluoride layers in the dielectric coating to less than 0.45, optimizing the balance between reflectivity and transmission. This parameter adjustment ensures sufficient transmission for interferometric measurements while maintaining high reflectivity through the optimized layer structure.
Solution Approach 2:
The patent uses a composite dielectric coating structure combining oxide layers and fluoride layers in a specific alternating arrangement. This composite structure leverages the complementary properties of both materials to achieve both high reflectivity and adequate transmission, while the oxide layers provide stress compensation to prevent cracking.
2Illumination intensity
If a dielectric coating with high proportion of fluoride layers is used to achieve high reflectivity, then reflectivity is improved, but stress-induced cracking increases
Solution Approach 1:
The patent employs a composite structure of oxide and fluoride layers where the oxide layers serve as stress-compensating elements. The alternating arrangement allows the more stress-resistant oxide layers to counterbalance the tensile stresses in the fluoride layers, preventing crack formation while maintaining high reflectivity.
Solution Approach 2:
By limiting the fluoride layer proportion to less than 0.45 and controlling the alternating layer structure, the patent optimizes the stress distribution within the coating. This parameter control ensures that stress concentrations do not reach critical levels that would cause cracking, thereby improving reliability.
3Loss of energy
If absorption is reduced to increase transmission, then transmission is improved, but the number of reflections needed for sufficient intensity increases
Solution Approach 1:
The patent optimizes the absorption parameter by selecting materials and layer configurations that minimize absorption losses. With absorption kept below 2% (particularly preferably below 1.5%), the coating allows sufficient transmission after multiple reflections, reducing the number of reflections needed to achieve the required intensity for accurate interferometric measurements.
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 provides high reflectivity between 93% and 97% with low absorption, enabling precise interferometric measurements and extended functionality of etalons by maintaining high transmission and reducing the risk of cracking.
Implementation Method 1
Depending on layer thicknesses, they have particularly high reflectivities at specific wavelengths
Implementation Method 2
dielectric coating has low refractive index and high refractive index dielectric layers in alternating arrangement
Implementation Method 3
any tensile stresses in the mixed layer stack can be compensated for by compressive stresses in the oxidic layer stack, such that the formation of cracks in the dielectric coating can be avoided
Implementation Method 4
the rays emerging from the etalon have different path differences and form different interference patterns
Implementation Method 5
two plane-parallel mirrors with dielectric coating are used to form, by way of spacers, an etalon, into which a partial ray of the radiation emitted by the laser is radiated and reflected to and fro between the two mirrors
Data Source
AI summary
A mirror with a dielectric coating (2) on a substrate (3), wherein the dielectric coating (2) has exactly two layer stacks (4, 5), a first layer stack (4), on the substrate, of layers (41, 42) of high refractive index and low refractive index oxides in alternating arrangement and a second layer stack (5), arranged thereon, of layers of fluorides (52) and oxides (51) in alternating arrangement, and wherein the number of fluoride layers (52) as a proportion of the total number of layers of the dielectric coating (2) is less than 0.45.