Photothermal Trace Gas Sensor with Intersecting Beams
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Solution Overview
Problem
Existing photothermal methods for detecting trace gases have a high sensitivity limit and require significant installation space, limiting their effectiveness in accurately measuring trace gas concentrations.
Innovation Solution
A method and sensor system that modulate electromagnetic excitation radiation and interrogation radiation at non-zero angles, generating differential signals filtered by modulation frequency to reduce common-mode noise and enhance sensitivity, allowing for precise detection of trace gas absorption with reduced sensitivity limits and compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If long-path cells are used to detect trace gases, then measurement precision is improved, but device complexity and installation space increase
Solution Approach 1:
The patent combines the excitation beam and probe beam paths to overlap within the sample chamber, creating a common-path interferometry system. This merging of beam paths eliminates the need for separate long-path cells while maintaining high measurement precision through interference-based detection of trace gas absorption.
Solution Approach 2:
The patent transitions from traditional linear long-path cell geometry to a three-dimensional overlapping beam configuration. The excitation and probe beams intersect within the sample volume, creating spatial interference patterns that encode absorption information, thereby achieving high sensitivity without extended path lengths in a single dimension.
2Measurement precision
If photothermal methods are used to detect trace gases, then measurement precision is improved, but installation space increases
Solution Approach 1:
The patent implements a nested beam configuration where the probe beam is positioned to overlap with and be modulated by the excitation beam within the sample chamber. This nested arrangement allows the probe beam to benefit from the excitation beam's interaction with the sample, achieving enhanced detection sensitivity within a compact volume rather than requiring separate large-scale photothermal equipment.
3Measurement precision
If excitation radiation is modulated to reduce noise, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent applies periodic modulation to the excitation radiation at a specific frequency, causing corresponding periodic variations in the probe beam intensity when absorbed by the sample. This periodic action enables frequency-based signal extraction through filtering, separating the analyte signal from background noise while using relatively simple modulation and detection electronics.
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 method achieves improved sensitivity and reduced noise interference, enabling the detection of trace gases at ppb to ppt levels with a more compact and sensitive photothermal absorption sensor system.
Implementation Method 1
the excitation frequency is equal to an absorption frequency of the sample; B) Periodically modulating the excitation radiation with a modulation frequency
Implementation Method 2
Capturing a first pattern intensity of an interference pattern of the probe radiation in the probe beam path behind the sample
Data Source
Figure 1
Figure 2a~3
AI summary
The present invention relates to a method for the photothermal determination of the absorption of electromagnetic excitation radiation in a sample, comprising the steps: A) generating the excitation radiation with an excitation intensity varying over an excitation beam cross-section and with an excitation frequency, wherein the excitation frequency is equal to an absorption frequency of the sample; B) periodically modulating the excitation radiation with a modulation frequency; C) illuminating the sample with the periodically modulated excitation radiation; D) generating electromagnetic probe radiation with a probe beam cross-section and a probe frequency, wherein the probe frequency is different from the excitation frequency; E) illuminating the sample with the probe radiation.such that an excitation beam path of the excitation radiation and a probe beam path of the probe radiation intersect at an angle other than zero degrees at an intersection point in the sample, and such that the probe beam cross-section is distributed over regions of the excitation beam cross-section with different excitation intensities, F) detecting a first pattern intensity of an interference pattern of the probe radiation in the probe beam path behind the sample at a first location in a detector plane as the first measurement signal, G) generating a detector signal from the first measurement signal, and H) filtering the first measurement signal or the detector signal according to the modulation frequency, so that an output signal is generated, wherein the output signal contains signal components of the first measurement signal modulated by the modulation frequency. According to the invention, it is proposed thatthat the method further comprises the steps: I) capturing a second pattern intensity of the interference pattern of the probe radiation at a second location in the detector plane as a second measurement signal, such that the phase of a periodic modulation of the first pattern intensity of the probe radiation at the first location caused by the periodic modulation of the excitation radiation is shifted by a value other than zero degrees or 360 degrees relative to the phase of the periodic modulation of the second pattern intensity of the probe radiation at the second location caused by the periodic modulation of the excitation radiation, and step G) comprises step a) forming a difference between the first measurement signal and the second measurement signal such that the detector signal is a differential signal, wherein step H) comprises filtering at least the first and the second measurement signal or the detector signal,so that the output signal contains signal components of the first measurement signal and the second measurement signal modulated at the modulation frequency.