Non-paraxial Multipass Cell for Ultra-long Path Spectroscopy
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Solution Overview
Problem
Existing multipass spectroscopy systems face challenges in achieving long path lengths without increasing the volume of the cell, and they are difficult to align and maintain, limiting their practical application.
Innovation Solution
The optical system employs a multipass cell with non-astigmatic mirrors and a short physical cell length, utilizing non-paraxial ray propagation to achieve a cumulative spot pattern that maximizes the intracavity path length, allowing for up to 2000 meters of propagation within a compact cell.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If standard Herriott cells or astigmatic cells are used to increase path length, then the intracavity path length increases, but the cell volume increases and alignment becomes difficult
Solution Approach 1:
The patent uses non-paraxial ray propagation to transition from traditional planar spot patterns to three-dimensional toroidal (doughnut-shaped) spot patterns on the mirror surfaces. This dimensional change allows the light beam to utilize the mirror surface area more efficiently, achieving much longer path lengths (10-2000 meters) within a compact cell volume of 1-50 cm without requiring proportional increases in cell size
Solution Approach 2:
The patent changes the propagation parameter from paraxial (small angle) to non-paraxial (large angle) ray propagation. This parameter change fundamentally alters the spot pattern geometry from simple loops to precessing toroidal patterns, enabling the light to cover the entire mirror surface area and achieve ultra-long path lengths in a compact configuration
2Area of stationary object
If astigmatic cells are used to create Lissajous patterns, then the mirror area utilization increases, but the alignment tolerances become tight and specific
Solution Approach 1:
The patent changes the fundamental propagation parameter from paraxial to non-paraxial, which transforms the spot pattern from astigmatic Lissajous figures to toroidal patterns with precession. This parameter change creates a more robust alignment regime where the light beam naturally samples the entire mirror surface area without requiring tight angular tolerances or specific alignment points
Solution Approach 2:
By transitioning to three-dimensional toroidal spot patterns on the mirror surface, the system achieves comprehensive mirror area utilization without the alignment sensitivity problems of astigmatic cells. The toroidal geometry naturally distributes the light path across the entire mirror surface, eliminating the need for precise alignment to specific points
3Productivity
If loop patterns are used to maximize mirror surface utilization, then the number of intracavity reflections increases, but the absolute path length remains short
Solution Approach 1:
The patent changes the propagation angle from small (paraxial) to large (non-paraxial), which transforms the spot pattern from simple loops to precessing toroidal patterns. This parameter change enables the light beam to traverse the entire mirror surface area with each pass, achieving absolute path lengths of 10-2000 meters while maintaining high numbers of intracavity reflections within a compact cell
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 enables a significant increase in the intracavity path length while maintaining a compact cell volume, improving the sensitivity of absorption spectroscopy measurements and simplifying alignment and maintenance.
Implementation Method 1
a first mirror having an injection aperture, and a second mirror that is spaced apart from the first mirror to form an optical cavity
Implementation Method 2
propagation of the light beam into the optical cavity is non-paraxial
Implementation Method 3
Absorption spectroscopy is a method of detecting, spectating, and quantifying molecular constituents in gaseous, liquid and solid samples by measuring the light absorbed
Implementation Method 4
the intensity of light transmitted through an absorbing material is governed by the Beer-Lambert Law
Data Source
AI summary
An optical system includes a light source, a multipass cell, and a detector. The multipass cell includes a first mirror and a second mirror spaced apart from the first mirror to form an optical cavity. A central axis extends between the first mirror and the second mirror. The light source outputs a light beam and is arranged to inject the light beam into the optical cavity of the multipass cell at an injection angle such that propagation of the light beam into the optical cavity is non-paraxial. The non-paraxial injection path and large-angle first reflection of the light beam causes the light beam to reflect back-and-forth between the first mirror and the second mirror to form a final (or cumulative) spot pattern that covers a large proportion of the surface areas of the first mirror and the second mirror before it exits the optical cavity.