Monolithic Cavity Interferometer for Opaque Part Flatness
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Solution Overview
Problem
Conventional interferometers face challenges in measuring the two-sided surfaces of opaque parts, particularly in determining flatness and parallelism, due to mechanical and thermal instabilities that affect the relative orientation of measurement arms, leading to unstable interference patterns.
Innovation Solution
A compound common-path interferometer with a monolithic measurement cavity, where the two measurement arms share a common optical reference cavity, isolating one arm from the other to minimize the transfer of disturbances, ensuring that object and reference beams propagate along common paths, maintaining stability despite thermal and mechanical influences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If two measurement arms are bolted together to maintain common orientation, then the ability to measure both sides of opaque parts is improved, but mechanical and thermal instabilities are transferred between arms causing interference pattern instability
Solution Approach 1:
The measurement system is divided into two independent measurement arms that are not mechanically connected. Each arm operates independently with its own support system, preventing the transfer of mechanical and thermal instabilities between arms while maintaining the capability to measure both sides of opaque parts
Solution Approach 2:
A common optical reference cavity serves as an intermediary element that both measurement arms access optically without mechanical connection. This allows the arms to share a common reference framework for measuring opposite sides of test parts while remaining mechanically isolated
2Manufacturing precision
If measurement arms are mechanically connected to maintain orientation, then spatial relationship between measurements is improved, but thermal and mechanical disturbances complicate measurements
Solution Approach 1:
The measurement arms are segmented into independent mechanically isolated units, each supported separately. This prevents thermal and mechanical disturbances from being transferred between arms while the common optical reference cavity maintains the necessary spatial relationships for accurate measurements
Solution Approach 2:
The mechanical connection between measurement arms is replaced with an optical connection through the common reference cavity. The spatial relationships are maintained through optical path geometry rather than mechanical rigidity, eliminating the transfer of mechanical and thermal disturbances
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 maintains stable interference patterns by ensuring that both reference surfaces and object beams are affected equally, reducing the impact of mechanical and thermal instabilities, thus providing accurate three-dimensional representations of opaque parts.
Implementation Method 1
Any optical path differences between object and reference beams of each measurement arm occur within the common optical reference cavity. The object and reference beams propagate along common optical paths within the remainder of each of the two measurement arms.
Data Source
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AI summary
A compound common-path interferometer including first and second measurement arms for measuring a test object is arranged so that a reference optic of the first measurement arm is not attached to the first measurement arm and a thermally stable spacer between the reference optics of the first and second measurement arms forms a monolithic measurement cavity for maintaining reference surfaces of the reference optics at a fixed spacing and orientation. Separate supports may be provided for the monolithic measurement cavity and th remainder of the first measurement arm.