Optical Test Surface Shape Determination Using Variable Incidence Angles
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Solution Overview
Problem
Current methods for measuring high-precision optical free form surfaces lack the ability to separate errors between the optical test surface and adaptation optics, particularly for non-rotationally symmetrical surfaces, leading to undetermined asymmetrical and symmetrical errors and incomplete averaging of shortwave interferometer errors.
Innovation Solution
A method involving adaptation optics that irradiates a measuring beam at different angles of incidence onto the optical test surface, allowing for the separation of errors by measuring the wavefront after interaction and removing the effect of adaptation optics from the interferometric measurement result, using an angle of incidence varying device and evaluation device to determine the shape of the optical test surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If rotation averaging is used to measure rotationally symmetrical surfaces, then shortwave interferometer errors are averaged and measurement precision is improved, but this method cannot be applied to free form surfaces lacking rotational symmetry
Solution Approach 1:
The patent applies asymmetry by using multiple illumination angles instead of rotational symmetry. For free form surfaces without rotational symmetry, the method illuminates the surface from different angular directions to obtain multiple wavefront measurements. This asymmetric approach allows separation of adaptation optics errors from test surface errors without requiring the test surface to have rotational symmetry, thus resolving the contradiction between measurement precision and adaptability to free form surfaces.
2Adaptability or versatility
If adaptation optics are used to measure free form surfaces, then measurement of non-rotationally symmetrical surfaces becomes possible, but error separation between adaptation optics and test surface becomes impossible
Solution Approach 1:
The patent applies dynamics by varying the illumination angle dynamically. Instead of using a fixed illumination geometry, the method changes the angle of incidence of the measuring beam across multiple measurements. This dynamic variation creates different lateral positions of test rays passing through the adaptation optics, enabling mathematical separation of errors contributed by the adaptation optics from those of the test surface, thus resolving the error separation problem while maintaining capability to measure free form surfaces.
Solution Approach 2:
The patent introduces another dimension by adding angular variation to the measurement process. Rather than measuring only at a single illumination angle, the method varies the angle of incidence as an additional degree of freedom. This dimensional extension creates lateral shearing effects that provide the necessary information to separate and eliminate adaptation optics errors from the measurement results.
3Measurement precision
If multiple measurement angles are used to separate errors, then error separation and averaging of shortwave errors are achieved, but measurement time increases
Solution Approach 1:
The patent applies periodic action by systematically varying the illumination angle across multiple measurements. The method uses a series of discrete angular positions that are periodically applied to the measurement process. This periodic angular variation enables both error separation and averaging of shortwave interferometer errors, while the structured approach allows for optimized measurement sequences that balance precision improvement with acceptable measurement time.
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 precise separation of errors between the optical test surface and adaptation optics, allowing for accurate determination of free form surfaces without rotational symmetry, and averages shortwave interferometer errors, improving measurement accuracy.
Implementation Method 1
the shape of the optical test surface is measured interferometrically by means of the adapted measuring beam
Implementation Method 2
At different angles of incidence the test rays pass through the individual surfaces in laterally different positions. Lateral shearing of the individual contributions of the wavefront originating from the components occurs.
Data Source
AI summary
A method of determining a shape of an optical test surface (14) includes: with adaptation optics (20), adapting a wavefront of a measuring beam (30) to a desired shape of the optical test surface (14), interferometrically measuring the shape of the optical test surface (14) with the adapted measuring beam, irradiating the adapted measuring beam at different angles of incidence onto the optical test surface and respectively measuring the wavefront of the measuring beam after the interaction of the measuring beam with the optical test surface (14), establishing the effect of the adaptation optics (20) upon the interferometric measurement result from the wavefronts measured for the individual angles of incidence, and determining the shape of the optical test surface (14) by removing the established effect of the adaptation optics (20) from the interferometric measurement result.