Ultra-Highly Sensitive Ammonia Detection Based on Light-Induced Thermoelastic Spectroscopy

Area of Science:

• Spectroscopy
• Chemical Sensing
• Laser Technology

Background:

• Ammonia (NH3) detection is crucial for environmental monitoring and industrial safety.
• Existing sensors often lack the required sensitivity and selectivity.
• The light-induced thermoelastic spectroscopy (LITES) technique offers potential for high-sensitivity gas sensing.

Purpose of the Study:

• To demonstrate an ultra-highly sensitive ammonia sensor for the first time using LITES.
• To investigate the performance of a quartz tuning fork (QTF) as a detector in this setup.
• To optimize the sensor parameters for achieving a low minimum detection limit (MDL).

Main Methods:

• Utilized light-induced thermoelastic spectroscopy (LITES) with a quartz tuning fork (QTF) detector.
• Employed a fiber-coupled distributed feedback (DFB) diode laser at 1530.33 nm as the excitation source.
• Applied wavelength modulation spectroscopy (WMS) and second-harmonic (2f) detection to enhance signal-to-noise ratio.

Main Results:

• Achieved a minimum detection limit (MDL) of approximately 5.85 ppm for ammonia.
• Demonstrated a linear relationship between the 2f signal amplitude and ammonia concentration (R-square ~0.99).
• Simultaneously acquired 2f signals from two distinct ammonia absorption lines.

Conclusions:

• The LITES technique, coupled with WMS and 2f detection, is effective for ultra-highly sensitive ammonia sensing.
• The developed sensor shows excellent linearity and a low MDL, suitable for practical applications.
• This work establishes a new benchmark for ammonia sensor sensitivity using optical spectroscopy.