研究目的
To develop a ppb-level formaldehyde detection system using a 3.6 μm interband cascade laser and mode-locked cavity enhanced absorption spectroscopy with self-calibration of the locking frequency.
研究成果
The developed system demonstrated a linear response to H2CO concentrations from 0 to 6 ppm and achieved a minimum detection limit of 5.8 ppb with a 30 s averaging time. The automatic PDH locking scheme effectively simplified the locking process and improved system stability.
研究不足
The system's sensitivity is limited by the cavity length and environmental interferences. The detection limit could be improved with a longer cavity.
1：Experimental Design and Method Selection:
The system uses a continuous-wave DFB-ICL emitting at
2：6 μm and an assembly F-P cavity with 20 m effective optical path length. The laser and cavity are locked to the H2CO absorption peak using an automatic PDH scheme. Sample Selection and Data Sources:
H2CO gas samples with concentrations from 0 to 6 ppm were used.
3：List of Experimental Equipment and Materials:
Includes a DFB-ICL, optical isolator, polarizer, electro-optic modulator, photodiode detectors, and a F-P cavity.
4：Experimental Procedures and Operational Workflow:
Involves dynamic PDH locking for spectrum acquisition and continuous PDH locking for gas concentration characterization.
5：Data Analysis Methods:
The cavity transmitted intensity was analyzed to determine H2CO concentration, with Allan deviation analysis used to assess system performance.
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optical isolator
IO-4-3400-WG
Thorlabs
Attenuate the optical feedback
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electro-optic modulator
EO-F25L3-IR
Qubig GmbH
Laser frequency modulation
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photodiode detector
PD-AC200-InGaAs
Thorlabs
Detect the transmitted beam exiting the F-P cavity
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photodiode detector
PIP-DC-200M-F-M4
VIGO
Receive the cavity reflected beam
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laser controller
D2-105-500
Vescent photonics
Control the laser
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pressure controller
Type 649B
MKS Instruments
Control and keep the pressure in the cavity
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interband cascade laser
DFB-ICL
Nanoplus
Light source for the detection system
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gas dilution system
Model 4040
Environics
Control the concentration and the flow rate of the sample gas
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