Interferometric Position Measurement with Beam Traps
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Solution Overview
Problem
Current interferometric devices face challenges in achieving high precision and repeatability in position measurements due to ambient influences and optical feedback, which lead to instability in laser frequency and measurement errors.
Innovation Solution
The implementation of a multi-beam splitter configuration with beam traps and detectors to minimize back reflections into the laser and interferometer, using 50/50 or 33/67 beam splitters to direct measuring light onto reflecting surfaces, and incorporating etalons for reference measurements, while adjusting elements ensure overlapping beams for accurate measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional interferometer setup is used for position measurement, then the device structure is simple, but optical feedback from the measuring stage into the laser causes instability in laser frequency and measurement errors
Solution Approach 1:
Beam splitters are introduced as intermediary optical elements between the laser and the interferometer paths. These beam splitters redirect the optical feedback away from the laser cavity, preventing the feedback from causing frequency instability while maintaining the interferometric measurement function. The beam splitters act as mediators that decouple the feedback path from the laser.
Solution Approach 2:
The optical path is segmented into multiple beam paths using additional beam splitters. Instead of a single direct path from laser to interferometer, the light is divided into first and second partial beam paths, with further segmentation into third partial beams. This segmentation allows selective redirection of feedback away from the laser while maintaining measurement paths.
2Stability of the object's composition
If beam splitters are added to redirect optical feedback away from the laser, then laser frequency stability is improved, but the device complexity increases
Solution Approach 1:
The beam splitters serve multiple functions simultaneously: they divide the main beam into partial beams for different interferometer paths, and they redirect optical feedback away from the laser cavity. This multi-functionality reduces the need for separate feedback management components, offsetting some of the complexity introduced by the additional optical elements.
Solution Approach 2:
The feedback redirection function is merged into the existing beam splitting optical paths. Instead of adding separate feedback management systems, the beam splitters that already exist in the interferometer setup are configured to also handle feedback redirection, combining two functions into a single optical element arrangement.
3Measurement precision
If multiple beam splitters are used to minimize back reflections, then measurement precision is improved, but the alignment and adjustment difficulty increases
Solution Approach 1:
The system uses optical feedback redirection through beam splitters to improve measurement precision by preventing feedback-induced frequency instability. The beam splitters are configured to redirect feedback away from the laser, and this feedback mechanism is built into the optical path design to automatically manage stability without requiring continuous manual adjustment.
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 configuration enhances the precision and repeatability of position measurements by reducing the impact of ambient influences and optical feedback, stabilizing the laser frequency, and minimizing measurement errors, thereby improving the accuracy of coordinate measuring machines.
Implementation Method 1
at least one first beam splitter for splitting the measuring light into a first partial beam path and a second partial beam path, which each impinge on a reflecting surface of the moveable element via an interferometer
Implementation Method 2
a second beam splitter, provided in the first or second partial beam paths for directing a third partial beam path onto an etalon for reference measurement via an interferometer
Implementation Method 3
a second beam splitter, provided in the first or second partial beam paths for directing a third partial beam path onto an etalon for reference measurement via an interferometer
Implementation Method 4
at least the first beam splitter, which splits the measuring light into a first partial beam path and a second partial beam path, and the third beam splitter, which directs the third partial beam path onto an etalon via an interferometer, and at least the first beam splitter, which splits the measuring light into a first partial beam path and a second partial beam path, and the second beam splitter, which directs the third partial beam path onto an etalon via an interferometer have a respective third beam splitter arranged downstream of them for directing the measuring light in the first partial beam path and the second partial beam path onto the respective reflecting surface of the measuring stage, or in that the beam splitter has a beam splitter arranged upstream of it, and in the first partial beam path and the second partial beam path respective reflecting elements are provided, which direct the measuring light onto the reflecting surface of the measuring stage
Data Source
AI summary
An interferometric device for position measurement of an element moveable in a plane is disclosed. A laser light source measures the position of the moveable element and emits the required measuring light. A beam splitter splits the measuring light into a first partial beam path and a second partial beam path, which each impinge on a reflecting surface of the moveable element via an interferometer. Herein, at least the beam splitter, which splits the measuring light into a first partial beam path and a second partial beam path, and the beam splitter, which directs the third partial beam path onto an etalon via an interferometer, have a respective beam trap associated with them, which traps the light returning from the respective interferometers.