Optical Resonator Calibration via Phase-Dependent Intensity Profiling
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Solution Overview
Problem
Current methods for calibrating optical resonators in absorption spectroscopy, such as CE-DOAS and BB-CEAS, face challenges in accurately determining the path length and reflectivity due to variable parameters like mirror reflectivity, temperature dependence, and environmental factors, leading to inconsistent and uncontrolled modulation of absorption structures, which affects the accuracy of trace gas concentration measurements.
Innovation Solution
A method involving the generation of light pulses with a known frequency, synchronized with a modulation frequency, and detection of light exiting the resonator for varying phase relationships to create a phase-dependent intensity profile, allowing for the calibration of optical resonators by characterizing this profile using characterization parameters, thereby determining the effective reflectivity and path length without consumables or gases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional calibration methods are used to determine path length and reflectivity, then calibration can be performed, but the measurements are affected by variable parameters such as mirror reflectivity, temperature dependence, and environmental factors, leading to reduced measurement precision and reliability
Solution Approach 1:
The patent applies periodic action by using light pulses with a known pulse frequency that is synchronized with a modulation frequency. The detection system modulates the detection signal with the modulation frequency and varies the phase relationship between the light pulses and the modulation. This periodic approach creates a phase-dependent intensity profile that can be characterized to determine path length and reflectivity, making the calibration process more precise and reliable by reducing the impact of variable environmental parameters.
2Measurement precision
If the path length is not accurately calibrated, then measurements can still be performed, but the absorption structures are modulated in an uncontrolled manner at different wavelengths, disturbing the convergence of the evaluation method and reducing measurement precision
Solution Approach 1:
The patent implements self-service by creating a phase-dependent intensity profile through synchronized light pulses and modulation, where the system characterizes its own response to determine the path length. The phase relationship between the light pulses and modulation frequency serves as an internal reference that allows the system to self-calibrate, ensuring accurate path length determination without requiring external calibration standards or complex reference measurements.
3Reliability
If traditional calibration approaches are used, then calibration can be performed, but consumables or gases are required, increasing operational costs and environmental influence
Solution Approach 1:
The patent eliminates the need for consumables by using the system's own light pulses and modulation response for calibration. The synchronized periodic action creates a self-contained calibration process where the phase-dependent intensity profile provides all necessary information for determining path length and reflectivity, making the system self-sufficient and eliminating dependency on external calibration gases or materials.
Solution Approach 2:
The patent changes the calibration approach from using physical consumables to using controllable parameter variations. By varying the phase relationship between the light pulse frequency and modulation frequency, and by adjusting the modulation frequency itself, the system creates different measurement conditions that allow calibration without consuming any physical substances, thereby improving reproducibility and eliminating consumable losses.
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 achieves high absolute accuracy and reproducibility in path length determination, reducing environmental influence and operational costs, enabling precise calibration of optical resonators for accurate trace gas concentration measurements.
Implementation Method 1
a folded light path, typically several kilometers long, is generated within an optical resonator between two highly reflective mirrors (reflectivity > 99%) by multiple reflection
Implementation Method 2
If (differential) absorbers are present between the mirrors, the (differential) absorption structures of the absorbers are impressed on the spectrum
Data Source
Figure 1
Figure 2
Figure 3a~3d
AI summary
The invention relates to a method and to a device for calibrating an optical resonator. The method comprises the following steps: generating light pulses of a known pulse frequency by means of a light-pulse generation unit; coupling the light pulses into the resonator (20); detecting light exiting the resonator (20) by means of a detection apparatus in order to generate a detection signal, wherein the detection apparatus is designed to generate the detection signal by means of a modulator as a signal modulated with a modulation frequency, wherein the modulation frequency is substantially equal to the pulse frequency of the generated light pulses or wherein the modulation frequency is substantially an integer multiple of the pulse frequency of the generated light pulses or wherein the pulse frequency of the generated light pulses is substantially an integer multiple of the modulation frequency; and calibrating the optical resonator (20) on the basis of the detection signal. The invention further relates to a use of the device according to the invention, to a use of a switchable detector or of an optical modulator, and to a computer program product.