Differential integrating sphere-based photoacoustic spectroscopy gas sensing

Area of Science:

• Optical Engineering
• Spectroscopy
• Gas Sensing

Background:

• Photoacoustic spectroscopy (PAS) is a sensitive technique for gas detection.
• Conventional PAS systems can suffer from noise and limited signal enhancement.
• Integrating spheres are used in optical systems to improve light collection and uniformity.

Purpose of the Study:

• To propose and demonstrate a novel differential integrating sphere-based photoacoustic spectroscopy (PAS) gas sensor.
• To enhance photoacoustic signal levels and improve noise suppression.
• To achieve a lower minimum detection limit (MDL) for gas sensing.

Main Methods:

• Design and implementation of a differential integrating sphere system comprising two integrating spheres and a tube.
• Utilizing differential characteristics for signal enhancement and noise reduction.
• Employing an erbium-doped fiber amplifier (EDFA) to boost diode laser output for optical excitation.

Main Results:

• The differential integrating sphere system demonstrated a 1.86-fold improvement in signal level compared to a single-channel system.
• The second harmonic (2f) signal of an acetylene (C2H2) PAS sensor reached 104.67 mV with EDFA amplification (1000 mW), a 22.80-fold increase.
• A minimum detection limit (MDL) of 416.7 ppb for C2H2 was achieved with a 100 s integration time.

Conclusions:

• The differential integrating sphere offers a new, advantageous method for PAS sensor development.
• This approach provides significant photoacoustic signal enhancement and strong noise immunity.
• The system eliminates the need for complex optical adjustments, simplifying its application.