Convex Mirror Interferometer for Tilted Surface Measurement
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Solution Overview
Problem
Areal surface interferometry faces challenges such as retrace errors, non-ideal phase shifting, environmental gradients, wavelength uncertainties, vibration, and noise, which limit its accuracy and introduce complexity, especially when measuring sloped or tilted surfaces, and existing displacement measuring devices like the spectral interferometric probe have slow measurement throughput and cannot handle surfaces tilted beyond a few degrees.
Innovation Solution
An interferometer system with a convex mirror configuration that allows light to be reflected and focused onto a fiber optic, enabling accurate displacement measurements without mechanical movement of the reference mirror or interferometer head, and includes photodetectors to detect surface tilt, allowing for high-accuracy measurements on sloped or tilted surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a spectral interferometric probe is used to measure displacement, then measurement accuracy is improved, but measurement throughput speed deteriorates
Solution Approach 1:
The patent replaces the mechanical scanning system with an optical field-based measurement approach. Instead of mechanically moving the reference mirror or interferometer head to scan across the surface, the invention uses a convex mirror to create multiple virtual light sources that simultaneously illuminate different surface locations. This substitution of mechanical movement with optical field distribution enables fast acquisition of displacement data across the entire measurement area while maintaining nanometer-level accuracy.
2Measurement precision
If a spectral interferometric probe is used to measure displacement, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The convex mirror serves multiple functions simultaneously: it acts as a beam splitter to create virtual light sources, functions as a focusing element to concentrate light onto the fiber optic, and serves as a reference surface for interference measurements. This multi-functionality reduces the number of separate optical components needed, thereby simplifying the overall device structure while maintaining measurement accuracy.
Solution Approach 2:
The patent merges the reference arm and measurement arm optical paths into a single integrated system. The convex mirror combines multiple light paths that would traditionally require separate optical trains, allowing the system to achieve interferometric measurements with fewer discrete components and reduced alignment complexity.
3Measurement precision
If a spectral interferometric probe is used to measure displacement, then measurement accuracy is improved, but adaptability to sloped surfaces deteriorates
Solution Approach 1:
The patent transitions from a one-dimensional linear scanning approach to a two-dimensional angular distribution approach. The convex mirror creates virtual light sources distributed in different angular directions, allowing the measurement beam to illuminate and collect light from sloped surfaces at various angles simultaneously. This dimensional change in the optical field distribution enables the system to measure surfaces with slopes up to 30 degrees while maintaining measurement accuracy.
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 and accurate displacement measurements on sloped or tilted surfaces, reducing retrace errors and increasing measurement throughput, while maintaining high precision and efficiency.
Implementation Method 1
The convex mirror is configured to receive diverging light from the fiber optic of the input/output arm and reflect a portion of that light into the measurement arm
Implementation Method 2
light reflected from the concave mirror of the measurement arm is brought to a focus at the surface under test
Implementation Method 3
Light reflected from the test surface is incident upon the concave mirror of the measurement arm which directs the light to the convex mirror which in turn reflects and focuses the measurement light onto the fiber optic
Implementation Method 4
The two re-collimated beams then form a spectral interference pattern on the image sensor of the camera
Implementation Method 5
a chromatic lens 28 that focuses the light in such a way that its focal position along an optical axis 18 varies with wavelength
Implementation Method 6
The linear piezo-electric transducer stage 22 can cause the measurement head 20, and its internal constituents, to move along the optical axis 18
Data Source
AI summary
An interferometer system for measuring the displacement of a location of a test surface includes a reference arm comprising two reflective optical elements with optical power, a measurement arm comprising two reflective optical elements with optical power wherein one of the optical elements of the reference arm is one of the optical elements of the measurement arm. A housing can be provided in which the reflective optical elements are mounted, all such components made from a material having a low CTE. Further, spider support structures can be provided for positioning a reflective optical element within the housing, and/or for positioning a fiber optic device within the system. Light detecting elements can be installed on a side of a spider support structure facing the test surface and used to detect a tilt of the test surface which can be used to improve the accuracy of the displacement measurement.