Plane-Mirror Spectrometer Layout for Long-Path Gas Sensing
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Solution Overview
Problem
Conventional gas absorption spectrometers using concave mirrors require high processing and assembly accuracy, leading to increased cost and device size.
Innovation Solution
A light measuring device utilizing two plane mirrors arranged non-parallel to each other, with an inclined optical path to form a long optical path, allowing for spatial separation of outward and return paths, and incorporating a quantum cascade laser and detector for high sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If concave mirrors are used to form a long optical path, then the sensitivity of absorption spectroscopy is improved, but the processing accuracy and assembly accuracy requirements increase, leading to increased cost and device size
Solution Approach 1:
The patent replaces expensive concave mirrors with simple plane mirrors that have no precision requirements for their reflective surfaces. The plane mirrors can be manufactured and assembled with standard tolerances, eliminating the need for high-precision processing and assembly while maintaining the long optical path functionality through multiple reflections between the two parallel plane mirrors
Solution Approach 2:
The patent changes the optical configuration from using curved surfaces (concave mirrors) to flat surfaces (plane mirrors). By introducing a slight tilt angle between the two plane mirrors, the system achieves spatial separation of the light path while using simple, inexpensive components that do not require high manufacturing precision
2Measurement precision
If concave mirrors are used to form a long optical path, then the sensitivity of absorption spectroscopy is improved, but the device size increases
Solution Approach 1:
The patent introduces a tilt dimension between the two plane mirrors, where the mirrors are positioned at a slight angle relative to each other. This tilts the multiple reflection path in the vertical direction, allowing the light to traverse a long optical path while keeping the horizontal footprint compact. The outward path and return path are spatially separated in the vertical dimension, enabling compact device design
3Measurement precision
If the optical path is arranged to separate outward and return paths spatially, then light measurement accuracy is improved, but the device complexity increases
Solution Approach 1:
The patent introduces asymmetry by tilting one of the plane mirrors relative to the other, creating a non-zero angle between them. This asymmetric configuration causes the multiple reflection path to tilt in space, automatically separating the outward light path from the return light path in the vertical direction. The separation is achieved through a simple angular adjustment rather than complex optical components
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
The device achieves simplification and miniaturization while maintaining high sensitivity for gas absorption measurements, reducing beam loss and interference, and enabling simultaneous measurement of multiple wavelengths.
Implementation Method 1
a light source unit configured to emit a laser beam
Implementation Method 2
a measurement target is introduced between the first mirror surface and the second mirror surface; a light detector configured to detect the laser beam returned by multiple reflection between the first mirror surface and the second mirror surface
Implementation Method 3
Since strong absorption derived from the fundamental vibration of molecules is observed in mid-infrared light (wavelength of 3 μm to 20 μm), the mid-infrared light is used for absorption spectroscopy (spectroscopic measurement) targeting gas molecules
Implementation Method 4
a light detector configured to detect the laser beam returned by multiple reflection between the first mirror surface and the second mirror surface
Data Source
AI summary
The spectrometer includes: a light source unit emitting a laser beam; a mirror unit including a first plane mirror having a first mirror surface and a second plane mirror having a second mirror surface, wherein a measurement target is introduced between the first mirror surface and the second mirror surface; and a light detector detecting the laser beam returned by multiple reflection between the first mirror surface and the second mirror surface. The first mirror surface and the second mirror surface are arranged non-parallel to each other when viewed from the Z-axis direction so as to form an optical path of the laser beam reciprocating in the Y-axis direction while performing multiple reflection between the first mirror surface and the second mirror surface. The optical path of the laser beam between the first mirror surface and the second mirror surface is inclined with respect to the Z-axis direction.