Multi-Wavelength Interferometer for Coated Surface Measurement
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Solution Overview
Problem
Interferometric measuring devices face limitations in measuring coated surfaces due to difficulty in distinguishing between reflections from the coating's outside and inside surfaces, and they have a limited measurement range, especially when operating in the visible spectral range.
Innovation Solution
The use of a multi-wavelength interferometric measuring device that generates a measurement beam with spectral components below 550 nm, employing a beam divider unit to extract partial beams of different center wavelengths, which increases the measurement range by creating a synthetic wavelength, and operates effectively with coated surfaces by selecting wavelengths where the coating is absorbent, reducing unwanted reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a single wavelength measurement beam is used, then the device structure is simple, but the measurement range is limited
Solution Approach 1:
The measurement beam is segmented into multiple wavelength components (first wavelength and second wavelength) with different center wavelengths. Each wavelength component provides a different measurement range, allowing the system to extend the overall measurement range by combining information from multiple segments rather than using a single wavelength.
Solution Approach 2:
The patent introduces a new dimension of measurement by adding wavelength diversity to the traditional single-wavelength interferometric measurement. By measuring at multiple wavelengths simultaneously, the system transforms a one-dimensional measurement approach into a multi-dimensional approach, enabling extended measurement range through synthetic wavelength calculation.
2Length of moving object
If visible wavelength light is used for measurement, then the device is cost-efficient and robust, but the measurement range is limited and coating reflections are difficult to distinguish
Solution Approach 1:
Different wavelength components are selected to have different interaction properties with the coating. The first and second wavelengths are chosen such that their absorption characteristics by the coating differ, allowing selective measurement of specific interfaces. This local quality differentiation in wavelength selection enables the system to distinguish between coating surfaces that would otherwise produce identical reflections.
Solution Approach 2:
The patent changes the wavelength parameter of the measurement beam to optimize measurement performance. By using multiple wavelengths with different center wavelengths and absorption characteristics, the system can penetrate the coating to measure underlying surfaces or selectively measure coating interfaces, overcoming the limited range and reflection interference problems of single-wavelength visible light measurement.
3Length of moving object
If the measurement beam wavelength is increased to extend measurement range, then the absolute distance range increases, but the spatial resolution and precision decrease
Solution Approach 1:
The measurement system is segmented into multiple wavelength channels, each providing different measurement capabilities. Shorter wavelengths provide high precision and resolution for local measurements, while longer wavelengths provide extended measurement range. By segmenting the measurement task across multiple wavelength segments, the system achieves both precision and extended range simultaneously.
Solution Approach 2:
The measurement system uses a composite approach by combining multiple wavelength components to create a synthetic measurement capability. The combination of different wavelength measurements allows the system to achieve the measurement range of long wavelengths while maintaining the precision of short wavelengths through composite signal analysis.
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 allows for precise and extended measurement range on coated surfaces, enhancing the device's reliability and adaptability while suppressing unwanted reflections, thereby improving measurement accuracy and robustness.
Implementation Method 1
The beam generating unit comprises at least a first light source. The beam generating unit and hence the first light source is operable to generate a measurement beam. The measurement beam comprises a spectral component at a wavelength smaller than 550 nm.
Implementation Method 2
a splitter to branch off an object beam and a reference beam from the measurement beam
Implementation Method 3
the object beam is directed onto the surface of the object and is reflected as a signal beam from the surface of the object
Implementation Method 4
When recombining the signal beam and the reference beam an optical interference can be observed being indicative of a runtime difference and hence of a path difference between the reference beam and the signal beam.
Implementation Method 5
operates effectively with coated surfaces by selecting wavelengths where the coating is absorbent, reducing unwanted reflections
Data Source
AI summary
An interferometric measuring device for measuring a surface or profile of an object includes a beam generating unit operable to generate a measurement beam with a spectral component at a wavelength smaller than 550 nm, a splitter to branch off an object beam and a reference beam from the measurement beam, a measurement probe connected to the beam generating unit and configured to direct the object beam onto the surface and to capture a portion of the object beam reflected from the surface as a signal beam, a signal analyzer connected to a detector unit and operable to derive a distance between the measurement probe and the surface on the basis of signals obtained from first and second detectors operable to detect first and second partial beams from an analysis beam being a recombination of the signal beam and the reference beam.