Interferometer Wavefront Error Calibration via Misalignment Mapping
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Solution Overview
Problem
Interferometric systems, such as Fizeau configurations, face performance degradation due to wavefront errors caused by misalignments, which are common in data acquisition and practical use, and existing methods lack a straightforward, cost-effective way to quantify and correct these errors.
Innovation Solution
A high-speed interferometric method that generates an empirically determined mathematical model of wavefront error as a function of aperture misalignment, using a reference leg and a measurement leg with alignment adjustments and two-dimensional detection to produce interference patterns, and applies correction functions based on error maps to compensate for tilt-induced errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If misalignment is introduced in interferometric systems for practical data acquisition, then ease of operation and adaptability are improved, but measurement precision deteriorates due to wavefront errors
Solution Approach 1:
The patent performs preliminary calibration by deliberately introducing known misalignments and measuring the resulting wavefront errors to create correction functions before actual measurements. This preliminary characterization of the system's error behavior enables subsequent correction of practical measurements taken at arbitrary misalignments, resolving the contradiction between ease of operation and measurement precision
Solution Approach 2:
The patent implements a feedback mechanism where measured wavefront errors from calibration interferograms are used to generate correction functions that are applied to subsequent measurements. This feedback loop continuously compensates for misalignment-induced errors, allowing the system to maintain high measurement precision even when operated at non-ideal misalignments for ease of use
2Measurement precision
If traditional calibration methods are used to correct ray-mapping errors, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent implements a self-service calibration approach where the interferometer uses its own measurement capabilities to characterize and correct its own errors. By measuring wavefront errors at different misalignments and generating self-correction functions, the system eliminates the need for external calibration equipment or complex manual procedures, reducing device complexity while maintaining measurement precision
Solution Approach 2:
The patent systematically varies misalignment parameters during calibration to map the relationship between misalignment and wavefront error. By changing these parameters in a controlled manner and fitting mathematical models to the data, the system creates efficient correction functions that achieve high measurement precision without requiring complex hardware modifications
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 method effectively corrects wavefront errors introduced by misalignment, improving measurement accuracy and reducing the sensitivity to environmental factors, while providing a cost-effective and deterministic calibration process.
Implementation Method 1
illuminating the test surface and the reference object with a wavefront that nominally is of the same shape as that of the test surface to produce interference patterns containing information about the instantaneous wavefront difference
Data Source
AI summary
Apparatus and methods for generating an empirically determined mathematical model of wavefront error in an interferometer as a function of aperture misalignment and then applying the model to correct subsequent measurements. The methods are useful in Fizeau and other types of interferometers in which carrier fringe analysis may be used for reducing errors caused by environmental and vibration effects.