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

Oscar E Bonilla-Manrique1, Julio E Posada-Roman2, Jose A Garcia-Souto2

  • 1Electronics Technology Department, Carlos III University of Madrid, 28911 Leganés, Spain. obonilla@ing.uc3m.es.

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Summary
This summary is machine-generated.

This study demonstrates a sensitive optical microphone for photoacoustic spectroscopy, achieving a low noise-equivalent absorption sensitivity for ammonia detection. The developed sensor shows promise for highly accurate gas analysis.

Keywords:
gas detectionmembraneoptical microphonephotoacoustic spectroscopyresonant cell

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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.