Laser Spectrometer Wavelength and Tuning Range Correction
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Solution Overview
Problem
Laser spectrometers face challenges in maintaining accurate wavelength and tuning range over time due to laser diode aging, leading to measurement inaccuracies and potential failure of evaluation algorithms, especially during large tuning ranges with non-linear components, which requires frequent recalibration and cannot be adjusted in-situ.
Innovation Solution
The method involves comparing the actual position of absorption lines with target positions in the absorption spectrum and adjusting the laser diode's temperature and current ramp slope to correct the wavelength and tuning range, using a combination of linear and non-linear current terms to account for non-linear tuning behavior, allowing for automatic correction during ongoing measurements without removing the device from the measurement setup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the laser diode is used for a long time, then the optical power decreases and wavelength changes due to aging, but frequent recalibration is required which disrupts measurement operations
Solution Approach 1:
The patent applies preliminary action by performing one-time adjustment procedures during manufacturing to store target positions of absorption lines. This pre-established reference data enables automatic correction during operation without requiring manual recalibration, thus maintaining wavelength stability while minimizing recalibration time and disruption to measurement operations.
Solution Approach 2:
The system implements self-service through automatic correction mechanisms that use stored target positions to self-adjust the laser spectrometer's wavelength and tuning range. The control device automatically compares actual absorption line positions with target positions and applies corrections without external intervention, eliminating the need for frequent manual recalibration and maintaining reliable operation over time.
2Adaptability or versatility
If the tuning range is increased, then more gas components can be measured, but non-linear components increase causing measurement inaccuracies
Solution Approach 1:
The patent applies parameter changes by adjusting the current ramp slope as a control parameter to compensate for non-linear effects in the laser diode's wavelength tuning. By dynamically modifying the current ramp characteristics based on comparisons between actual and target absorption line positions, the system maintains measurement precision across an extended tuning range, enabling versatile gas component detection without sacrificing accuracy.
3Measurement precision
If the current ramp slope is adjusted to correct wavelength drift, then the wavelength position is improved, but the tuning range changes
Solution Approach 1:
The patent applies dynamics by implementing a two-stage correction process that dynamically adjusts different parameters in sequence. First, the laser diode temperature is adjusted to correct wavelength position drift, then the current ramp slope is modified to restore the tuning range. This dynamic, multi-step approach ensures that both wavelength precision and tuning range adaptability are maintained simultaneously, with each parameter adjustment compensating for the effects of the previous adjustment.
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 ensures accurate and reliable wavelength and tuning range correction, maintaining measurement precision and avoiding the need for frequent recalibration, as the laser spectrometer automatically adjusts to compensate for aging-related changes, ensuring consistent performance without disrupting ongoing measurements.
Implementation Method 1
a time-resolved absorption spectrum of the gas is obtained upon detection of the light
Implementation Method 2
the concentration of a gas component of interest is determined based on the reduction in light intensity caused by the absorption of the light at a selected absorption line
Implementation Method 3
the temperature of the laser diode is changed until the actual position corresponds to the target position
Implementation Method 4
the slope of the current ramp is changed until the actual position corresponds to the target position
Data Source
Figure 1~4
Figure 5~9
AI summary
In a laser spectrometer the light from a wavelength-tunable laser diode (3) after radiating through a gas (1, 18) is detected and evaluated, wherein the laser diode (3) is periodically driven with a current ramp (9), such that a time-resolved absorption spectrum of the gas (1, 18) is obtained upon the detection of the light (4). In order to correct the wavelength and the tuning range of the laser spectrometer, a first step involves readjusting the central wavelength of the laser diode (3) by way of the temperature thereof and on the basis of the position of one of two different selected absorption lines in the detected absorption spectrum, and a second step involves correcting the tuning range of the laser diode (3) by way of the gradient of the current ramp (11) such that the spacing of the two absorption lines in the detected absorption spectrum remains constant.