Phase-Scrambling Sample Cell for Gas Spectroscopy
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Solution Overview
Problem
Conventional direct absorption spectroscopy methods face challenges in accurately measuring gaseous sample compositions due to interfering optical interference effects caused by the sample cell's optical windows, which can obscure weak absorption signals and lead to drifting spectral features.
Innovation Solution
A phase-scrambling sample cell with a reflective inner surface and reduced pressure is used, featuring a diverging laser beam and a pressure control system to minimize interference effects, allowing for accurate measurement of spectral transmittance by scrambling the phase of the laser radiation and maintaining an absolute pressure below 50 kPa.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional optical windows are used in the sample cell, then the cell can effectively confine the sample gas, but disturbing interference effects occur that obscure weak absorption signals
Solution Approach 1:
The patent removes the conventional optical windows from the sample cell and replaces them with a reflective inner surface coating applied directly to the cell walls. This extraction of the window element eliminates the parallel optical surfaces that cause interference effects while maintaining the sample confinement function through the reflective coating.
Solution Approach 2:
The patent introduces a reflective inner surface coating as an intermediary layer on the sample cell walls. This coating serves as a mediator that provides both sample confinement and eliminates interference effects by preventing the formation of interferometric fringes that occur with conventional parallel window surfaces.
2Device complexity
If optical windows are used to define the absorption path length, then the cell structure is simple, but interferometric effects cause spectral features to drift
Solution Approach 1:
The patent extracts the optical windows from the cell structure and replaces them with an integrated reflective coating on the cell walls. This eliminates the separate window components that create interferometric effects while maintaining the absorption path length definition through the reflective surface geometry.
Solution Approach 2:
The patent changes the optical parameters of the cell by applying a reflective coating with specific reflectivity characteristics to the inner surface. This parameter change eliminates the interferometric effects caused by parallel window surfaces while maintaining the cell's structural simplicity and absorption path length definition.
3Measurement precision
If coherent laser radiation is used for measurement, then the spectral resolution is high, but interference fringes from the cell windows obscure weak absorption signals
Solution Approach 1:
The patent converts the harmful interferometric effects into a beneficial outcome by eliminating the parallel optical surfaces that cause them. The reflective inner surface coating maintains the coherent laser radiation's high spectral resolution while preventing the generation of interference fringes that would obscure weak absorption signals.
Solution Approach 2:
The reflective inner surface coating acts as an intermediary that allows coherent laser radiation to maintain its high spectral resolution properties while preventing the generation of interference fringes. The coating modifies the optical path in a way that preserves coherence benefits without introducing the harmful interferometric effects of parallel window surfaces.
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 significantly reduces or eliminates interference effects, enabling more precise measurement of gaseous sample compositions, including carbon monoxide and carbon dioxide, with improved stability and reduced need for calibration, allowing for faster data acquisition and better accuracy.
Implementation Method 1
the specular reflectance of the inner surface is smaller than 50% such as to scramble the phase of the transmitted light
Implementation Method 2
the divergence of the illuminating light beam is greater than 30° so as to cause multiple consecutive reflections from the inner surface
Implementation Method 3
maintain an absolute pressure of the gaseous sample inside the sample cell smaller than 50 kPa so as to reduce spectral widths of spectral features of the gaseous sample
Implementation Method 4
The divergence of the illuminating light beam is greater than 30° so as to cause multiple consecutive reflections from the inner surface
Implementation Method 5
The sample contained in the cell may attenuate the transmitted light at certain wavelengths, corresponding to the absorption peaks of the sample
Implementation Method 6
The composition of a gaseous sample may be analyzed by using direct absorption spectroscopy
Data Source
Figure 1a~1b
Figure 2~3
Figure 4~5
AI summary
A measuring apparatus (500) for measuring a spectrum (SPEC1 ) of a gaseous sample (GAS1) comprises: - a tunable laser light source (LS1 ) to provide an illuminating light beam (LBO), - a sample cell (200) for containing the gaseous sample (GAS1 ), the cell (200) comprising an inner surface (SRF1) to provide scrambled light (LB1) by reflecting light of the illuminating light beam (LB0) such that the scrambled light is transmitted through the gaseous sample (GAS1), - a detector (DET1) to detect intensity (ILB2) of transmitted scrambled light (LB2) guided through the sample cell (200), and - a pressure control system (VAC1) to maintain an absolute pressure (PGAS1) of the gaseous sample (GAS1) smaller than 50 kPa inside the sample cell (200) so as to reduce spectral widths of spectral features of the gaseous sample (GAS1), wherein the measuring apparatus (500) is arranged to measure one or more spectral transmittance values (ILB2(λ)/Ιο(λ)) of the sample (GAS1 ) by modulating the spectral position (λLB0) of the illuminating light (LB0), and by detecting the intensity (ILB2) of the transmitted light (LB2) at two or more different spectral positions (λ0, λP1) of the illuminating light (LB0), wherein the longitudinal dimension (LSRF1) of the inner surface (SRF1 ) is in the range of 10 to 100 times a minimum diameter (dSRF1) of the inner surface (SRF1), and wherein the divergence (θLB0) of the illuminating light beam (LB0) in a transverse direction is greater than 30° so as to cause multiple consecutive reflections of the scrambled light (LB1 ) from the inner surface (SRF1 ).