Mirror Substrate with Low Thermal Expansion for Precision Polishing
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Solution Overview
Problem
Current technologies face challenges in producing mirror substrates with high aspect ratios, low weight, and high surface quality, particularly for substrates with small thickness and large diameter, due to issues with thermal expansion and accuracy during polishing processes.
Innovation Solution
The development of mirror substrates made from materials with a coefficient of mean linear thermal expansion of less than or equal to 1*10−6/K, combined with a support having a similar thermal expansion coefficient, allows for precise polishing and maintenance of dimensional stability during processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a mineral-based casting support is used for full-surface support during polishing, then the mirror substrate is supported over the entire surface to maintain dimensional stability, but the different thermal expansion between the support and the low-expansion mirror substrate material causes inaccuracies in geometrical dimensions and surface quality
Solution Approach 1:
The support is made from the same low-expansion glass ceramic material as the mirror substrate, ensuring homogeneous thermal expansion characteristics. This eliminates differential thermal expansion during polishing operations, allowing both the support and mirror substrate to expand and contract uniformly with temperature changes, thereby maintaining dimensional accuracy and surface quality.
2Weight of moving object
If the mirror substrate has a high aspect ratio with large diameter and small thickness, then the weight is reduced and handleability is improved, but deformation occurs under the intrinsic weight of the mirror substrate degrading optical image quality
Solution Approach 1:
The invention changes the material parameter by using low-expansion glass ceramic with specifically controlled thermal expansion properties. This material parameter change allows the mirror substrate to maintain form stability under its own weight while keeping the weight low, as the material's inherent properties prevent deformation that would otherwise occur with conventional materials.
3Manufacturing precision
If extensive polishing processes are performed to achieve high surface quality, then the surface roughness is reduced, but a large amount of heat is generated causing thermal expansion differences between the support and mirror substrate
Solution Approach 1:
By making the support from the same low-expansion glass ceramic material as the mirror substrate, the system achieves homogeneous thermal response during polishing. The identical material composition ensures that both components experience the same thermal expansion when heat is generated during extensive polishing operations, preventing relative dimensional changes and maintaining surface quality accuracy.
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
This approach enables the production of mirror substrates with high aspect ratios, low weight, and exceptional surface quality, overcoming previous limitations in form stability and surface accuracy.
Implementation Method 1
a material having a coefficient of mean linear thermal expansion of less than or equal to 1*10−6/K
Data Source
AI summary
A mirror, a mirror substrate, a method for producing are provided. The mirror substrate is made of a material having a coefficient of mean linear thermal expansion of less than or equal to 1*10−6/K. The mirror substrate includes at least one feature selected from a group consisting of: a ratio of a lateral dimension to a maximum thickness of at least 100, a ratio of the lateral dimension to the maximum thickness of at least 150, a ratio of the lateral dimension to the maximum thickness of at least 200, a ratio of the lateral dimension to the maximum thickness of at least 300, a weight per unit area of 100 kg/m2 or less, a weight per unit area of 50 kg/m2 or less, a weight per unit area of 30 kg/m2 or less, a weight per unit area of 15 kg/m2 or less, a mirror surface with a roughness (Ra) of at most 3.5 μm, and a mirror surface with a roughness (Ra) of less than 1.2 μm.