Interferometer Beamsplitter Mounting with Three-Pin Alignment
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Solution Overview
Problem
Michelson interferometers face challenges in maintaining optical alignment due to environmental forces and thermal changes, leading to inaccuracies in measurements, especially when materials with appropriate reflectance/transmittance properties for specific wavelengths are not available for constructing the entire interferometer from a single material.
Innovation Solution
The use of a frame with components made from different materials having similar coefficients of thermal expansion, along with a three-pin mounting arrangement, to minimize exposure of optical elements to bending, warping, and distorting, and to facilitate easy maintenance and alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a monolithic interferometer constructed from a single material is used, then thermal stability and alignment accuracy are improved, but material selection is limited and cost increases
Solution Approach 1:
The patent changes the material parameter by selecting materials with matched coefficients of thermal expansion. The frame is made of one material (e.g., metal alloy) while optical elements are made of different materials (e.g., glass, crystal), but all materials are selected to have similar CTE values. This parameter matching allows multi-material construction without suffering from thermal expansion mismatch, thereby maintaining alignment accuracy while gaining material selection flexibility for optimal optical performance.
Solution Approach 2:
The patent employs composite construction by combining multiple materials in a single interferometer structure. The frame and optical elements are made from different materials that are mechanically bonded together. This composite approach allows each component to be made from the most suitable material for its function (structural support vs. optical performance) while the CTE matching ensures thermal stability is maintained across the composite structure.
2Ease of manufacture
If optical elements are mounted using traditional mounting methods, then assembly is simple, but alignment accuracy deteriorates due to mounting stresses
Solution Approach 1:
The patent introduces a compliant mounting layer or intermediate structure between the rigid frame and the optical elements. This intermediary component absorbs mounting stresses and prevents them from being transmitted to the optical elements. The compliant layer acts as a stress decoupling mechanism, allowing simple assembly while protecting alignment accuracy by isolating optical elements from frame stresses.
3Adaptability or versatility
If the interferometer is made from multiple materials with different coefficients of thermal expansion, then material properties can be optimized for specific functions, but thermal distortion increases
Solution Approach 1:
The patent changes the thermal parameter by carefully selecting and matching the coefficients of thermal expansion of different materials used in the interferometer. Each material is chosen to have a CTE that is compatible with adjacent materials, preventing differential thermal expansion. This parameter matching enables the use of multiple materials with optimized functional properties (mechanical strength, optical transmission, reflectivity) while maintaining thermal stability of the overall structure.
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 ensures high accuracy measurements by reducing external stresses and maintaining optical alignment, allowing for the use of multiple wavelength light sources and easy replacement of optical assemblies, thereby reducing costs and maintenance efforts.
Implementation Method 1
Michelson interferometers function by splitting a beam of electromagnetic radiation into two separate beams via a beam splitter
Implementation Method 2
A reflecting element, such as a retroreflector, is placed in the path of each beam and returns them both to the beam splitter
Implementation Method 3
The beams are there recombined into a single exit beam. The variable path length causes the combined exit beam to be amplitude modulated due to interference between the fixed and variable length beams
Data Source
AI summary
A frame for optics used in interferometers that may include different materials having substantially similar, identical, or as close as practicable coefficients of thermal expansion from the material(s) used to make the beamsplitter and/or compensator without warping, bending, tilting or distorting the optics. The beamsplitter and/or compensator are mounted onto the frame of the interferometer using a three-point method of mounting, preferably using three pins for each component. Preferably, the pins are made of the same material as the beamsplitter and compensator, and all three components are made of Potassium Bromide (“KBr”) or Calcium Fluoride (“CaF2”) such that the optic instrument can operate to scan into the mid or far infrared. Stability in optical alignment is therefore achieved without requiring the optic instrument include only one material. The invention provides stability in situations where it is not possible to utilize a single material for every component of the interferometer.