Compact Multipass Cell with Planar Beam Propagation
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Solution Overview
Problem
Conventional multipass cells are unsuitable for applications with limited space and low sample volume due to their large size and high production costs, and they often require complex alignment and suffer from diffraction issues.
Innovation Solution
A multipass cell with a rectangular cavity and concave spherical or toroidal mirrors positioned at a distance corresponding to twice their radius of curvature, allowing a beam to propagate in a single plane with a linear reflection spot pattern, reducing volume requirements and improving manufacturing ease.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional multipass cells are used to increase optical pathlength, then detection sensitivity is improved, but device volume becomes too large for applications with limited space
Solution Approach 1:
The patent transitions from conventional circular beam patterns to a planar reflection spot pattern where the beam propagates substantially in a single plane between mirrors. This dimensional change from 3D circular paths to 2D planar paths enables compact cell design while maintaining long optical pathlength, directly resolving the contradiction between detection sensitivity and device volume
Solution Approach 2:
The patent employs concave spherical or toroidal mirrors with specific curvature radii to focus the beam between mirrors positioned at distances corresponding to twice the radius of curvature. This curved mirror geometry enables the beam to maintain a stable single-plane propagation pattern over multiple reflections, achieving both compact volume and extended optical pathlength
2Measurement precision
If conventional multipass cells are used to increase optical pathlength, then detection sensitivity is improved, but manufacturing cost increases due to difficulty in producing high optical surface quality
Solution Approach 1:
The patent divides the optical system into separate planar mirror components rather than requiring a single complex circular multipass structure. This segmentation into manageable planar sections with linear reflection patterns simplifies manufacturing and alignment while achieving the same sensitivity enhancement through extended optical pathlength
Solution Approach 2:
The patent employs asymmetric positioning of mirrors at distances corresponding to twice the radius of curvature to create a focused single-plane beam pattern. This asymmetric configuration simplifies manufacturing compared to symmetric circular patterns while maintaining the optical pathlength needed for high detection sensitivity
3Ease of manufacture
If separate section mirrors are used to reduce manufacturing cost, then ease of manufacture is improved, but alignment complexity increases and diffraction problems occur at mirror edges
Solution Approach 1:
By confining beam propagation to a single plane between mirrors rather than allowing 3D circular paths, the patent dramatically simplifies alignment requirements. The planar geometry provides natural reference planes that guide mirror positioning, reducing alignment complexity while maintaining cost-effectiveness through segmented mirror sections
Solution Approach 2:
The patent extracts the beam propagation path from the mirror edges by positioning the beam to travel through the central region between mirrors. This extraction of the beam path from edge-proximity eliminates diffraction problems at mirror edges while preserving the benefits of separate section mirrors for cost-effective manufacturing
4Volume of stationary object
If mirrors are positioned to focus the beam between them at twice the radius of curvature distance, then optical path-to-volume ratio is improved, but precise positioning requirements increase
Solution Approach 1:
The patent specifies mirror distances corresponding to twice the radius of curvature of concave spherical or toroidal mirrors. This curvature-based positioning provides self-focusing geometry that naturally guides the beam between mirrors, achieving compact volume with extended optical path while the geometric relationship provides inherent alignment references that reduce the practical precision burden
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 design achieves a high optical path-to-sample volume ratio with straightforward alignment, robustness against misalignment, and cost-effective production, enabling scalable and efficient optical detection systems.
Implementation Method 1
a first concave spherical or toroidal mirror at a first end of the cavity; and a second concave spherical or toroidal mirror at the opposite end of the cavity; wherein the first mirror and the second mirror are configured to reflect a beam entering the cavity
Implementation Method 2
the first mirror and the second mirror are positioned at a distance corresponding to twice the radius of curvature of the first and the second mirrors in such a way that the beam is focused between the first and the second mirror
Data Source
Figure 1a~1b
Figure 2~3
Figure 4~5
AI summary
A multipass cell (100), comprising a body (10); a cavity (20) formed within the body (10); a first spherical, toroidal or cylindrical mirror (30a) at a first end of the cavity (20); and a second spherical, toroidal or cylindrical mirror (30b) at the opposite end of the cavity. The first mirror (30a) and the second mirror (30b) are configured to reflect a beam entering the cavity next to an outer edge of the first (30a) or the second (30b) mirror a predetermined number of times so that the beam propagates substantially in a single plane between the first (30a) and the second (30b) mirror. Also an optical detection system comprising the multipass cell; an optical source (110) configured to direct a beam into the cavity (20); and a detector element (120) configured to receive the beam exiting the cavity (20) or configured to receive the acoustic signal generated by light absorption in the cavity (20).