Sub-ppm-Level Ammonia Detection Using Photoacoustic Spectroscopy with an Optical Microphone Based on a Phase...

Area of Science:

• Optics
• Spectroscopy
• Acoustics

Background:

• Photoacoustic spectroscopy (PAS) is a sensitive gas detection technique.
• Traditional PAS systems can be limited by acoustic noise and transducer sensitivity.

Purpose of the Study:

• To develop a sensitive optical microphone for photoacoustic spectroscopy.
• To enhance gas detection performance and suppress background noise.

Main Methods:

• Utilized a fiber laser Doppler vibrometer (FLDV) with phase-generated carrier demodulation.
• Employed a resonant gas cell and a slim Teflon diaphragm as an acoustic transducer.
• Used wavelength modulation spectroscopy with second harmonic detection for ammonia (NH3) detection.

Main Results:

• Achieved a minimum detectable pressure of 79.5 μPa/√Hz.
• Demonstrated a noise-equivalent absorption sensitivity of 1.85 × 10⁻⁸ W cm⁻¹/√Hz for NH3.
• Reported a limit of detection of 785 ppbv for ammonia.

Conclusions:

• The developed optical microphone offers high sensitivity and effective background noise cancellation for gas sensing.
• The system shows potential for precise and sensitive detection of trace gases like ammonia.