Interferometer Reference Mirror for Robust Spatial Frequency
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Solution Overview
Problem
Existing interferometric measuring devices face challenges in achieving long-term stability and simplicity for measuring distance, depth, and surface profiles due to complex alignment requirements and susceptibility to misalignments, which limits their ability to change spatial frequency and measurement range effectively.
Innovation Solution
The use of a three-plane-mirror reference end reflector in the interferometer introduces a constant lateral shear, allowing for robust and cost-effective measurement by maintaining the spatial frequency of spatial interferograms independent of object surface inclination, and is invariant to misalignments caused by environmental changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a downstream inclination device (tilting mirror) is used to create spatial interferograms, then spatial frequency invariance to object surface inclination is achieved, but device complexity and alignment difficulty increase significantly
Solution Approach 1:
The patent extracts the inclination function from the traditional downstream tilting mirror and relocates it to the reference beam path. By placing the tilting mirror in the reference beam path instead of the downstream position, the device achieves spatial frequency invariance while reducing overall system complexity and improving alignment stability.
Solution Approach 2:
The patent employs a curved reference mirror instead of a flat mirror in the reference beam path. This curvature enables the generation of spatial interferograms with invariant spatial frequency to object surface inclination, while the curved geometry provides inherent alignment stability and reduces sensitivity to misalignments.
2Ease of operation
If a downstream inclination device is used, then spatial interferograms can be generated, but long-term stability decreases due to susceptibility to misalignments
Solution Approach 1:
The patent performs preliminary alignment stabilization by placing the tilting mirror in the reference beam path where it can be precisely aligned and fixed before measurement. This preliminary positioning in a stable optical path ensures long-term alignment stability and reduces susceptibility to environmental misalignments during operation.
Solution Approach 2:
The patent creates a stable reference copy of the optical path by using a curved reference mirror that replicates the inclination effect in the reference beam. This reference copy remains stable and invariant, providing a reliable basis for interferogram generation without being affected by object surface variations or environmental misalignments.
3Adaptability or versatility
If the spatial frequency for centroid wavelength is changed by means of an inclination device, then spatial frequency adjustment is possible, but lateral offset of wavefronts occurs requiring complex compensation
Solution Approach 1:
The curved reference mirror serves multiple functions simultaneously: it generates the required spatial interferograms, provides spatial frequency invariance to object inclination, and inherently compensates for lateral wavefront offsets. This multi-functionality eliminates the need for separate compensation mechanisms and reduces overall alignment complexity.
Solution Approach 2:
The curved reference mirror acts as an intermediary element that mediates between the reference beam and object beam. By introducing controlled curvature in the reference path, it enables spatial frequency adjustment while automatically compensating for lateral offsets through its geometric properties, without requiring complex additional compensation devices.
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 enables accurate and stable measurement of distance, depth, and surface profiles with high measurement accuracy and robustness, suitable for microform, microprofile, and roughness measurements, including on non-cooperative surfaces, and supports optical coherence tomography with multi-point scanning.
Implementation Method 1
The use of a three-plane-mirror reference end reflector in the interferometer introduces a constant lateral shear
Implementation Method 2
an interferometer, in particular also in the form of an interference microscope, having an object beam path and having at least one reference beam path
Data Source
AI summary
An arrangement and a method are provided for robust interferometry for detecting distance, depth, profile, form, undulation, flatness deviation and/or roughness or the optical path length in or on technical or biological objects, including in layered form, or else for optical coherence tomography (OCT), with a source of electromagnetic radiation and with an interferometer, in particular also in the form of an interference microscope, having an object beam path and having a reference beam path, in which an end reflector is arranged, and a line-scan detector for detecting electromagnetic radiation in the form of at least one spatial interferogram.