Ultrasensitive, real-time trace gas detection using a high-power, multimode diode laser and cavity ringdown...

Area of Science:

• Spectroscopy
• Environmental Science
• Analytical Chemistry

Background:

• Cavity Ringdown (CRD) spectroscopy offers high sensitivity for trace gas detection.
• Traditional CRD techniques can be susceptible to vibrations, limiting field applications.
• Nitrogen dioxide (NO2) is a key air pollutant requiring sensitive monitoring.

Purpose of the Study:

• To develop a simplified, vibration-insensitive CRD technique for trace gas detection.
• To achieve high sensitivity and real-time absorption measurements.
• To demonstrate the technique's suitability for field deployment.

Main Methods:

• Utilized a high-power, multimode Fabry-Perot (FP) diode laser with a broad wavelength range.
• Employed on-axis cavity alignment for improved signal-to-noise ratio.
• Tested the technique by measuring low concentrations of nitrogen dioxide (NO2) in zero air.

Main Results:

• Achieved a sensitivity of 38 parts per trillion (ppt) with a 128 ms integration time.
• Demonstrated single-shot detection sensitivity of 530 ppt with a 60 μs measurement time.
• Confirmed vibration insensitivity by introducing external vibrations without affecting detection sensitivity.

Conclusions:

• The simplified CRD technique is robust against vibrations, enabling reliable field measurements.
• The broad laser linewidth eliminates the need for precise wavelength stabilization.
• This method provides unprecedented speed for NO2 concentration measurements using CRD spectroscopy.