Interferometer System for Tilted Surface Metrology
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Solution Overview
Problem
Existing surface metrology techniques, such as areal interferometry, face challenges with accuracy and complexity, particularly when measuring polished and tilted surfaces, due to retrace errors and the need for precise fabrication of test spheres and null correctors, which limits the precision and throughput of displacement measurement systems.
Innovation Solution
An interferometer system incorporating a measurement arm with a dispersive optical system and a reference arm featuring a bulk diffuser object, combined with a digital processing system to determine displacement, utilizing a broadband light source and filtering to enhance spectral resolution and accuracy, allowing for high-precision displacement measurement across a wide range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If areal interferometry is used for surface measurement, then measurement speed and accuracy are improved, but device complexity and manufacturing precision requirements increase due to need for test spheres and null correctors
Solution Approach 1:
The patent extracts the reference arm from traditional areal interferometry by replacing test spheres and null correctors with a broadband light source and spectral interferometry. This removes the complex optical components while maintaining measurement capability through wavelength-dependent interference patterns that can be captured and processed digitally.
Solution Approach 2:
The patent replaces mechanical optical components (test spheres, null correctors) with a spectral interferometry system that uses wavelength modulation. Instead of mechanically adjusting optical paths with precision optics, the system uses spectral dispersion and digital processing to achieve the same measurement function with simpler hardware.
2Productivity
If chromatic probe is used for displacement measurement, then measurement speed is improved, but measurement precision deteriorates due to inadequate spectral image processing
Solution Approach 1:
The patent implements feedback through spectral interferometry where the interference pattern provides continuous information about displacement. The spectral fringes modulate the light intensity according to the optical path difference, creating a feedback signal that can be precisely measured and processed to determine displacement with high accuracy while maintaining fast measurement rates.
Solution Approach 2:
The patent changes the measurement parameter from simple intensity modulation (chromatic probe) to spectral interference pattern analysis. By measuring the wavelength-dependent interference fringes and analyzing their phase and amplitude characteristics, the system achieves both fast measurement and high precision through the rich information content in the spectral domain.
3Adaptability or versatility
If chromatic probe measures tilted surfaces, then measurement capability is maintained, but measurement precision deteriorates due to light loss from high-angle reflections
Solution Approach 1:
The patent introduces spectral interferometry as an intermediary measurement method that doesn't rely on direct back-reflection from the surface. Instead, it measures the phase shift of light that has interacted with the surface, allowing accurate measurement of tilted surfaces without the light loss problems of traditional chromatic probes that require strong back-reflected light signals.
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
The system achieves fast displacement measurement rates with high accuracy, capable of measuring uncooperative surfaces, offering a balance between the speed of chromatic probes and the precision of spectral interferometers, while reducing errors associated with surface tilt and polish.
Implementation Method 1
a broadband light source and filtering to enhance spectral resolution and accuracy
Implementation Method 2
a reference arm featuring a bulk diffuser object
Implementation Method 3
Interferometer systems and methods thereof
Data Source
AI summary
An interferometer system includes a measurement arm comprising a measurement dispersive optical system, a reference arm comprising a bulk diffuser object and a reference dispersive optical system, and an output system. The measurement dispersive optical system is positioned to direct measurement chromatic light towards a target, receive diverging chromatic measurement light from the target, and direct detected measurement light from the received diverging chromatic measurement light towards the output system. The reference dispersive optical system is positioned to direct reference chromatic light towards the bulk diffuser object, receive diverging chromatic reference light from the bulk diffuser object, and direct detected reference light from the received diverging chromatic reference light towards the output system. The output system is configured to determine at least one measured property of the target from the detected measurement light and the detected reference light.