Interferometer Retrace Error Correction for Optical Surface Deviation
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Solution Overview
Problem
Current interferometric systems lack precision in measuring deviations of optical surfaces from target shapes, particularly for non-rotationally symmetric surfaces and nano free form surfaces, due to inaccuracies in wave front deviation measurements and retrace errors.
Innovation Solution
The method involves directing an incoming beam of electromagnetic radiation onto the optical test surface to generate a measuring beam, performing interferometric measurements by superimposing a reference beam, and correcting wave front deviations by eliminating retrace errors caused by aberrations accumulated during measurement, allowing for precise alignment and calibration adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If interferometric measurement is performed on optical surfaces with wave front deviation larger than 10*λ, then measurement coverage is improved, but retrace error increases causing measurement precision to deteriorate
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing reference wave front deviations for multiple known optical surface shapes in a database before actual measurement. During measurement, the system retrieves the appropriate reference data and compares it with measured values, eliminating the need for iterative alignment adjustments and reducing retrace errors.
Solution Approach 2:
The patent introduces an intermediary computational model that simulates ideal interferometric measurements for various optical surface shapes. This computational intermediary provides reference wave front deviations that mediate between the complex physical measurement process and the final measurement results, enabling accurate measurement without direct physical iteration.
2Adaptability or versatility
If zero lenses or compensators are used to produce aspherical wave fronts for measuring aspherical optical surfaces, then measurement capability is improved, but device complexity increases
Solution Approach 1:
The patent replaces the mechanical/optical system of zero lenses and compensators with a computational approach. Instead of using physical optical elements to generate and analyze aspherical wave fronts, the system uses computer-based simulation and database storage to model ideal measurements, thereby eliminating complex optical components while maintaining measurement capability.
Solution Approach 2:
The patent creates computational copies of ideal interferometric measurement patterns for various optical surface shapes. These digital copies serve as references that can be stored and retrieved, eliminating the need for physical optical elements to generate each measurement pattern and simplifying the overall device architecture.
3Measurement precision
If alignment adjustments are performed to minimize wave front deviation, then measurement accuracy is improved, but measurement time increases
Solution Approach 1:
The patent performs preliminary action by pre-calculating the ideal wave front deviations for various optical surface shapes and storing them in a database. During actual measurement, the system directly compares measured values with pre-stored references, eliminating the time-consuming iterative alignment process while maintaining high measurement accuracy.
Solution Approach 2:
The patent transforms the static, iterative alignment process into a dynamic, direct comparison process. By pre-computing reference patterns and enabling direct comparison with measured data, the system dynamically adapts to different optical surface shapes without requiring physical realignment, thereby reducing measurement time while maintaining 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 accurate measurement and correction of wave front deviations with an accuracy of less than 1 nm, effectively addressing the limitations of existing systems in precision and applicability to non-rotationally symmetric surfaces.
Implementation Method 1
performing a use measurement by an interferometer by superimposing a reference beam with the measuring beam to determine a wave front deviation of the measuring beam from the reference beam
Data Source
AI summary
A method of measuring a deviation of an optical test surface from a target shape is provided. The method includes directing an incoming beam of electromagnetic radiation onto the test surface to generate a measuring beam that has interacted with the test surface, causing the ray that has interacted with the test surface to pass through an interferometer on a deviated path, performing an interferometric measurement by superimposing a reference beam with the measuring beam to determine a wave front deviation of the measuring beam from the reference beam, determining a retrace error in the wave front deviation, and correcting the measured wave front deviation by eliminating the retrace error therefrom. The differences in aberrations accumulated by the ray having traveled on the deviated path from fictitious aberrations that would have been accumulated by a ray that had traveled on an undeviated path cause the retrace error.