Wavelength Scanning Interferometer for Aspheric Surface Measurement
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Solution Overview
Problem
Existing methods for measuring aspheric surfaces are limited by low accuracy, high measurement time, risk of surface damage, and the need for complex and costly multi-dimensional translation platforms and compensation components.
Innovation Solution
A wavelength scanning interferometer system that uses a tunable laser, a translation platform, a light splitter, and a CCD camera to measure the absolute optical path difference of an aspheric surface without the need for zero compensation components, allowing for high-accuracy, non-contact measurement of aspheric surfaces with varying apertures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional contact stylus methods are used for aspheric surface measurement, then measurement can be performed, but measurement time is time-consuming and there is risk of damaging the measured surfaces
Solution Approach 1:
The patent replaces the mechanical contact stylus measurement system with an optical interference measurement system. The optical method uses light waves to measure surface shape through interference patterns, eliminating the need for physical contact between the measurement probe and the aspheric surface. This substitution of mechanical measurement with optical measurement simultaneously achieves high accuracy and fast measurement speed, resolving the contradiction between measurement precision and measurement time.
2Measurement precision
If interferometers based on subaperture stitching are used, then measurement can be performed, but high-accuracy multi-dimensional rotary translation platform is required increasing device complexity
Solution Approach 1:
The patent extracts and eliminates the complex multi-dimensional rotary translation platform from the measurement system. By using a simplified linear translation mechanism combined with wavelength scanning, the system achieves the same measurement capability without requiring high-accuracy multi-dimensional rotary positioning. This extraction of the complex component directly reduces device complexity while maintaining measurement precision.
3Measurement precision
If shear interferometers are used for surface shape reconstruction, then measurement can be performed, but accumulative measurement errors are introduced due to slope integral measurement
Solution Approach 1:
The patent inverts the measurement approach by directly measuring the optical path difference corresponding to the surface height at each point, rather than measuring slope information and integrating to reconstruct the surface shape. This direct measurement method avoids the cumulative errors inherent in slope integration, significantly improving measurement reliability while maintaining precision.
4Measurement precision
If interferometers using computer-generated holography and zero compensation lens are used, then measurement can be performed, but errors are introduced by compensation components
Solution Approach 1:
The patent removes the zero compensation lens and other complex compensation components from the measurement system. By using wavelength scanning interferometry with a simple linear translation mechanism, the system achieves accurate measurement without requiring these additional components that introduce errors. This extraction of problematic components directly improves measurement reliability.
5Measurement precision
If additional length measurement interferometer is used for measuring displacement, then measurement can be performed, but system complexity and cost are increased
Solution Approach 1:
The patent makes the wavelength scanning interferometer system universal by enabling it to perform both optical path difference measurement and displacement measurement through a single system. The same interferometric setup measures both the surface shape and the translation displacement without requiring separate dedicated instruments, thereby reducing system complexity and cost while maintaining precision.
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 high measurement accuracy and flexibility, reducing measurement time and costs by eliminating the need for complex translation platforms and compensation components, while ensuring the reliability of the measurement process.
Implementation Method 1
a light beam emitted by the tunable laser is expanded by the beam expander to become a parallel light beam
Implementation Method 2
the lights reflected by the reference mirror and the measured aspheric surface are re-superposed on the light splitter to form interference
Implementation Method 3
a light beam emitted by the tunable laser is expanded by the beam expander to become a parallel light beam
Implementation Method 4
the wavefront is split into two beams by the light splitter
Implementation Method 5
interference fringes are acquired by the CCD camera after passing through the imaging lens
Implementation Method 6
encounter optical-electric conversion in the CCD camera and then analogue-digital conversion in the image card
Data Source
AI summary
The present invention discloses a wavelength scanning interferometer and a method for an aspheric surface measurement. The wavelength scanning interferometer comprises a set of tunable lasers (7) used as a light source, a Twyman-Green interferometer used for generating interference fringes, a translation platform (1) used for scanning an optical path difference along an optical axis, an image card (11) used for converting interference data to a digital signal and transmitting the digital signal to a computer (12), and a data card (13) used for synchronizing the actions of a CCD camera (9) and the translation platform (1). Different from the traditional aspheric surface measurement method, the interferometer is capable of measuring a surface with a high aspheric surface degree or a wavefront, and without the need of a zero compensation mirror. In addition, the method does not need a complex and usually expensive multi-dimensional movement platform.