CRDS Laser Frequency Locking Using Harmonic Conversion Feedback
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Solution Overview
Problem
Conventional CRDS devices using the PDH method require high-precision control of the laser light's oscillation frequency to maintain high measurement accuracy and sensitivity, which increases costs and limits measurement efficiency due to narrow longitudinal mode pulse line widths.
Innovation Solution
A gas absorption spectroscopic measurement device and method that uses a frequency locking technique by converting the laser light's frequency to an integral multiple, allowing for wider error signal acquisition and feedback control, reducing the need for high-precision frequency control and enabling faster frequency locking and maintenance of oscillation and mode frequency coincidence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-precision control of laser oscillation frequency is implemented to maintain measurement accuracy and sensitivity, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent implements a feedback control mechanism where the error signal generated by the PDH method is fed back to control the laser oscillation frequency. The feedback control unit adjusts the laser frequency based on the error signal to maintain coincidence with the optical resonator mode frequency, thereby achieving high measurement precision without requiring overly complex control systems.
Solution Approach 2:
The patent changes the parameter of laser frequency multiplication by outputting laser light at an integral multiple of the fundamental frequency. This parameter change expands the error signal acquisition range, allowing the system to achieve frequency locking with relaxed precision requirements, thus reducing device complexity while maintaining measurement accuracy.
2Measurement precision
If narrow longitudinal mode pulse line width is used to achieve high detection sensitivity, then measurement sensitivity is improved, but the range for error signal acquisition narrows
Solution Approach 1:
The patent applies frequency multiplication to the laser output, generating light at an integral multiple of the fundamental frequency. This parameter change effectively expands the frequency range over which error signals can be acquired, allowing the system to maintain narrow longitudinal mode pulse line widths for high sensitivity while gaining broader frequency adaptability.
Solution Approach 2:
The patent introduces a frequency multiplication dimension to the system. By operating at harmonics of the fundamental frequency, the system accesses additional frequency domains where error signals can be effectively generated, thereby expanding the acquisition range without compromising the narrow line width needed for high sensitivity.
3Productivity
If frequency multiplication is applied to expand error signal acquisition range, then frequency locking speed is improved, but device complexity increases
Solution Approach 1:
The patent introduces a frequency conversion unit as an intermediary component that generates laser light at an integral multiple of the fundamental frequency. This intermediary device enables rapid frequency locking by providing access to a broader error signal range, while its modular design keeps the added complexity manageable and justified by the significant improvement in locking speed.
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 allows for high-accuracy and sensitive CRDS measurements without the need for precise laser frequency control, increasing measurement efficiency and reducing costs, while enabling rapid frequency alignment and broader frequency range measurements.
Implementation Method 1
an optical resonator configured to cause light emitted from the laser irradiation unit to resonate
Implementation Method 2
a gas absorption spectroscopic measurement device and method that uses absorbance to laser light
Data Source
AI summary
The gas absorption spectroscopic measurement device according to one embodiment of the present invention is provided with: a laser irradiation unit (1); and optical resonator (2), and a first detection unit (3) for detecting light taken out of the optical resonator (2). The gas absorption spectroscopic measurement device acquires the component concentration of a gas to be measured by CRDS (Cavity Ring-Down Spectroscopy) measurement. The laser irradiation unit (1) is provided with: a laser light source (10); a frequency conversion unit (12) configured to selectively output either laser light having the same frequency as the irradiation light source or laser light having a frequency of the laser light source multiplied by a prescribed number of times; a frequency modulation unit (13, 14) for modulating the frequency of the emitted laser light using a modulation signal, a second detection unit for detecting returning light derived from the irradiation light returning to the optical resonator (2); and a feedback control unit (191, 11) for generating an error signal affected by the difference between the frequency of the laser light emitted to the optical resonator (2) and the modulation signal based on the detection signal from the second detector (18), thereby controlling the oscillation frequency in the laser light source (10) in accordance with the error signal.