Interferometer ITF Optimization via Digital Focus Correction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing optical instruments for measuring surface form and texture face challenges in accurately resolving and measuring surface features due to factors like imperfect focus, environmental disturbances, and optical limitations, which affect the reliability and repeatability of instrument transfer function (ITF) measurements.
Innovation Solution
The method involves using an artifact with known spatial frequency content to measure the instrument transfer function (ITF) by normalizing and differentiating the surface profile, digitally transforming the data to correct for focus errors, and employing phase shifting interferometry to extract the frequency content of surface features, thereby optimizing the accuracy and repeatability of ITF evaluation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional ITF measurement methods are used, then the measurement process is simple, but the measurement precision is reduced due to focus errors and environmental disturbances
Solution Approach 1:
The method performs preliminary digital transformation of the measured surface data to a different focal plane before analyzing the ITF. By pre-correcting the focus errors through digital propagation to an optimized surface, the measurement process compensates for focus imperfections before they degrade the measurement precision, thereby resolving the contradiction between simple procedure and high precision.
Solution Approach 2:
The patent introduces an intermediary digital processing step that transforms the measured surface data to a different focal plane using diffraction theory. This intermediary transformation acts as a mediator that separates the focus error effects from the actual ITF measurement, allowing the system to achieve high precision without requiring perfect mechanical focus.
2Reliability
If measurements are taken at the nominal surface, then the process is straightforward, but focus errors reduce the reliability of the ITF evaluation
Solution Approach 1:
The method performs preliminary digital transformation of the measured surface data to a different focal plane before analyzing the ITF. By pre-correcting the focus errors through digital propagation to an optimized surface, the measurement process compensates for focus imperfections before they degrade the measurement precision, thereby resolving the contradiction between simple procedure and high precision.
Solution Approach 2:
The patent introduces an intermediary digital processing step that transforms the measured surface data to a different focal plane using diffraction theory. This intermediary transformation acts as a mediator that separates the focus error effects from the actual ITF measurement, allowing the system to achieve high precision without requiring perfect mechanical focus.
3Measurement precision
If the instrument is used in real environmental conditions, then the instrument is practical for application, but environmental disturbances reduce measurement accuracy
Solution Approach 1:
The patent introduces an intermediary digital processing step that transforms the measured surface data to a different focal plane using diffraction theory. This intermediary transformation acts as a mediator that separates the focus error effects from the actual ITF measurement, allowing the system to achieve high precision without requiring perfect mechanical focus.
Solution Approach 2:
The method changes the evaluation parameter by measuring at a different focal plane than the nominal surface. By digitally propagating the data to an optimized surface where the focus errors are minimized, the system achieves higher measurement precision despite environmental disturbances during the actual measurement process.
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 enhances the accuracy and reliability of ITF measurements by minimizing errors from focus imperfections and environmental factors, providing a robust metric for evaluating instrument performance and ensuring precise spatial frequency analysis.
Implementation Method 1
Phase shifting interferometry can be used to measure the surface profile of the artifact
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Method include using an apparatus to measure a first surface field, at a first surface of the apparatus, of an artifact having one or more surface features with known topography. The method includes determining a first focus metric at the first surface based on at least a portion of a first surface profile containing the one or more surface features. Methods include digitally transforming, the first surface field into a second surface field at a second surface of the apparatus, deriving, a second surface profile from the second surface field and computing a second focus metric for the second surface profile, and determining, based on two or more focus metric values, an optimum surface for evaluating the instrument transfer function. Method include determining the instrument transfer function of the apparatus based on at least a portion of the surface profile derived from the surface field of the optimum surface.