Interferometric Surface Shape Measurement Using Diffractive Optical Elements
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Solution Overview
Problem
Diffractive optical elements cause measurement errors in interferometric methods, reducing the accuracy of determining optical surface shape.
Innovation Solution
Use two diffractive optical elements with different diffraction structures to generate test waves that correspond to the same points on the surface, capturing interferograms sequentially to minimize measurement errors by eliminating interference radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a diffractive optical element is used to generate test waves with wavefronts adapted to the target surface, then the measurement capability for complex optical surfaces is improved, but measurement errors are introduced due to interference radiation
Solution Approach 1:
The patent changes the diffraction properties of the optical element by using multiple diffractive optical elements with different diffraction structures. Each element has distinct diffraction efficiencies and interference patterns, allowing the system to capture multiple interferograms with varying interference characteristics. By combining these interferograms, the system maintains measurement capability while reducing the impact of interference radiation through computational processing.
2Measurement precision
If multiple diffractive optical elements with different configurations are used to eliminate interference errors, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent makes the measurement arrangement multi-functional by enabling the same optical setup to capture multiple interferograms with different diffraction characteristics. The evaluation device performs multiple functions: capturing individual interferograms, identifying interference patterns, and computationally combining them to eliminate errors. This software-based approach reduces hardware complexity compared to using physically separate measurement systems.
Solution Approach 2:
The patent employs periodic action by sequentially capturing multiple interferograms using different diffractive optical elements. The system systematically varies the diffraction configuration across multiple measurements, allowing the evaluation device to identify and eliminate interference patterns through their periodic variation. This structured repetition enables error elimination without requiring complex real-time adjustments.
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
Improves measurement accuracy by reducing the influence of interference radiation, enhancing the precision of determining optical surface shape.
Implementation Method 1
arranging a first diffractive optical element in the beam path of an input wave to generate a first test wave with a wavefront at least partially adapted to a target shape of the optical surface
Implementation Method 2
acquiring a first interferogram generated by the first test wave after interaction with the surface of the test object
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A measuring method for interferometrically determining a shape of a surface (12) of a test object (14) comprises the steps of arranging a first diffractive optical element (30, 130, 230) in the beam path of an input wave (18) for generating a first test wave (34) with a wavefront at least partly adapted to an intended shape of the optical surface, capturing a first interferogram generated by means of the first test wave following an interaction with the surface (12) of the test object (14), arranging a further diffractive optical element (32, 232) in place of the first diffractive optical element in the beam path of the input wave for generating a further test wave with a wavefront at least partly adapted to the intended shape of the optical surface (12), the first diffractive optical element and the further diffractive optical element differing in the configuration of the relevant diffraction structures, capturing a further interferogram generated by means of the further test wave following an interaction with the surface (12) of the test object (14), and determining the shape of the surface of the test object by combining the two interferograms by calculation.