Segmented Circular Multipass Cell Mirrors for Longer Optical Paths
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Solution Overview
Problem
Traditional multipass cells face limitations in fabrication due to their monolithic metal structure, which restricts the internal diameter to 20 cm and makes it difficult to achieve high surface uniformity and reflectivity, leading to limited optical path length and cumulative light loss, hindering widespread adoption.
Innovation Solution
A method of manufacturing segmented circular multipass cells by forming mirrors on a planar substrate, allowing for standard surface structuring, coating, and polishing, and assembling into a closed polygonal geometry, enabling the use of standard techniques like moulding, etching, and machining to enhance reflectivity and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a monolithic metal structure is used for manufacturing multipass cells, then the structural integrity is maintained, but the internal diameter is restricted to 20 cm and fabrication difficulty increases
Solution Approach 1:
The multipass cell is divided into multiple planar substrate segments that are assembled to form the complete optical cavity. Each segment can be manufactured independently using standard techniques, allowing the overall internal diameter to exceed 20 cm while maintaining ease of fabrication. The segments are joined together to form the closed polygonal geometry required for the multipass cell operation.
2Loss of energy
If metallic coatings are deposited on mirror surfaces, then the mirrors are formed, but the reflectivity is limited and cumulative light loss increases
Solution Approach 1:
The mirror surfaces are formed using composite material structures, combining planar substrate segments with deposited reflective coatings. This approach allows for optimized surface uniformity through precise substrate preparation followed by controlled coating deposition, achieving high reflectivity while minimizing cumulative light loss through the multiple passes required in multipass cell operation.
3Manufacturing precision
If the closed-geometry nature is maintained, then the optical path is defined, but coating or polishing of mirror surfaces becomes impossible or very difficult
Solution Approach 1:
The mirror surfaces are prepared in advance on flat planar substrate segments before assembly. This preliminary preparation allows standard coating and polishing techniques to be applied effectively to achieve high surface uniformity. After the reflective surfaces are formed on the individual segments, the segments are then assembled into the closed polygonal geometry, avoiding the difficulty of working with curved surfaces in a closed cavity.
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 allows for the production of segmented circular multipass cells with improved reflectivity and optical path length, overcoming fabrication constraints and enabling longer optical paths without exponential light loss, facilitating broader adoption.
Implementation Method 1
The light beam then propagates within the multipass cell reflecting from mirror to mirror following a m-star polygram reflection pattern
Implementation Method 2
To avoid beam divergence and minimise beam spot size on the mirror segments, the mirrors can be shaped to provide a confocal configuration
Data Source
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AI summary
A method of manufacturing a segmented circular multipass cell. Starting from a planar substrate (20) with upper and lower surfaces (22, 24) surface structure is applied by one or more of moulding, milling, etching, die-sinking, and machining. A first surface structure forms a plurality of parallel grooves (25) in the planar substrate (20) which subdivide the substrate into segments (12) and allow the substrate (20) to be rolled up into a closed polygonal form by hinging along the grooves (25). A second surface structure provides respective ones of the segments (12) with mirror-shaped surfaces (15) which face inwards when the substrate (20) is rolled up. The mirror-shaped surfaces (15) are processed into high-reflectivity mirrors (14) while the substrate is planar, i.e., before it is rolled up, thereby enabling convential mirror manufacturing processes to be applied, such as deposition of metal or dielectric coatings and polishing.