Ppb-level detection of nitric oxide using an external cavity quantum cascade laser based QEPAS sensor

Area of Science:

• Optics and Spectroscopy
• Chemical Sensing
• Laser Technology

Background:

• Photoacoustic spectroscopy (PAS) offers high sensitivity for gas detection.
• Quartz-enhanced photoacoustic spectroscopy (QEPAS) enhances sensitivity through a quartz tuning fork.
• Mid-infrared quantum cascade lasers (QCLs) provide tunable, high-power light sources for molecular spectroscopy.

Purpose of the Study:

• To optimize micro-resonator geometrical parameters for enhanced photoacoustic spectroscopy.
• To achieve sensitive and background-free spectroscopic measurements for gas detection.
• To apply the optimized sensor for nitric oxide (NO) detection.

Main Methods:

• Optimization of micro-resonator geometrical parameters for QEPAS.
• Utilizing a widely tunable, mode-hop-free external cavity quantum cascade laser (QCL).
• Applying the optimized QEPAS sensor to detect nitric oxide (NO) at 1900.08 cm(-1).

Main Results:

• Achieved a nitric oxide (NO) detection sensitivity of 4.9 parts per billion by volume (ppbv).
• Demonstrated sensitive detection with 1-second averaging time and 66 mW optical power.
• Determined optimal gas pressure (210 Torr) and water vapor concentration (2.5%) for NO detection.

Conclusions:

• The optimized QEPAS sensor enables sensitive and background-free NO detection.
• The study highlights the potential of QEPAS for trace gas analysis.
• Water addition was found to improve the NO vibrational-translational relaxation process.