Parallel-Face Substrate Surface Analysis Without Back Reflection Interference
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Solution Overview
Problem
Existing methods for analyzing the surface quality of parallel-sided blades, particularly those that are transparent, face challenges due to interference from the back face reflection, requiring complex setups, handling-sensitive operations, and environmental sensitivity, especially when using low-coherence light sources.
Innovation Solution
A method using wavefront analyzers with low temporal coherence light sources and spatially coherent beams to analyze both faces of a parallel-sided blade by receiving reflection and transmission beams, eliminating interference effects and enabling direct wavefront measurement without complex setups or environmental sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a transparent blade is analyzed using optical methods, then the surface quality can be studied, but reflection from the back face interferes with the measurement
Solution Approach 1:
The patent extracts and eliminates the harmful back-face reflection component from the measurement system. By using a Shack-Hartmann wavefront sensor, the system separately measures and subtracts the back-face reflection contribution from the total signal, isolating the front-face surface deformation measurement from the interfering back-face reflections.
Solution Approach 2:
The patent introduces a reference wavefront as an intermediary element in the measurement process. This reference wavefront serves as a baseline for comparing the actual wavefront after it passes through the blade, enabling the system to identify and separate the back-face reflection effects from the front-face surface information.
2Measurement precision
If phase-shifting interferometry methods are used to eliminate back surface reflection effects, then measurement accuracy improves, but the system becomes complex and requires precise alignment
Solution Approach 1:
The patent replaces complex mechanical interferometer systems with an electronic/digital processing approach. Instead of using physical phase-shifting mechanisms and precise mechanical alignment of interferometers, the system uses a Shack-Hartmann wavefront sensor combined with mathematical algorithms to achieve the same measurement objectives with significantly reduced mechanical complexity.
3Measurement precision
If frequency-tunable laser sources are used for interference measurements, then back face reflection can be separated, but numerous data acquisitions are required making the system sensitive to vibrations
Solution Approach 1:
The patent uses a single wavelength light source instead of multiple wavelengths, and performs a single wavefront measurement instead of multiple sequential measurements. This partial action approach achieves the measurement objective without requiring numerous data acquisitions, thereby eliminating sensitivity to vibrations and environmental changes.
4Object-generated harmful factors
If coating is applied to the back surface to suppress reflection, then back face reflection is eliminated, but coating and cleaning operations are required which can introduce surface deformations
Solution Approach 1:
The patent enables the measurement system to automatically compensate for and eliminate back-face reflection effects through mathematical processing, without requiring any physical modification of the blade surface. The system uses the blade's own optical properties and the measured wavefront data to self-correct for back-face interference, avoiding the need for coating applications or cleaning operations.
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
Enables accurate and efficient analysis of both faces of parallel-sided blades using cheaper, less complex, and more robust systems, suitable for various thicknesses and shapes, without the need for environmental control or specific wavelength filters.
Implementation Method 1
reception by at least a first wavefront analyzer of wavefront analysis means, of at least a first reflection beam and a second reflection beam, said first reflection beam resulting from the reflection of said at least a first light beam by a first face of the blade
Implementation Method 2
said second reflection beam resulting from a first transmission of the blade by said first light beam then from a reflection by a second face of the blade followed by a second transmission of the blade
Implementation Method 3
the emission by at least a first light source of emission means, of at least a first light beam with low temporal coherence
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
The invention relates to a method for analysing the surface quality of a substrate (100) comprising: - emitting a first light beam (221) which is incident on a first face (A) of said substrate; - receiving, by wavefront analysis means (240), a first reflected beam (222a) resulting from the reflection of the first beam by the first face, and a second reflected beam (222b) resulting from a reflection by a second face (B) of the substrate, in order to generate at least one first measurement signal which is characteristic of a combination of the wavefronts of the first and second reflected beams; - receiving, by the wavefront analysis means, a transmitted beam resulting from transmission through the substrate by a second light beam in order to generate a second measurement signal; - calculating, from the first and second measurement signals, a first signal and a second signal which represent a deformation of the first face and of the second face, respectively.