A Dual-Enhancement Fiber-Optic Photoacoustic Spectroscopy Sensor Based on a Spherical-Cylindrical Coupled Resonator...

Area of Science:

• Optical Engineering
• Spectroscopy
• Sensor Technology

Background:

• Conventional spherical resonators limit photoacoustic spectroscopy (PAS) sensitivity due to detection aperture interference with acoustic resonance.
• Acoustic resonance optimization is crucial for enhancing PAS sensitivity.

Purpose of the Study:

• To develop a novel dual-enhancement fiber-optic PAS sensor for ultrahigh-sensitivity gas detection.
• To overcome the sensitivity limitations of conventional spherical resonators in PAS.

Main Methods:

• Integration of a multipass cell (MPC) within a novel spherical-cylindrical (SC) coupled resonator.
• Utilizing a cylindrical waveguide for noninvasive photoacoustic signal detection.
• Employing a two-mirror MPC within the coupled cavity for optical path length extension.

Main Results:

• Achieved a 1.72-fold acoustic enhancement via the SC coupled resonator design.
• Realized an optical enhancement factor of over 15 using the integrated MPC.
• Demonstrated a 26-fold overall sensitivity improvement compared to conventional spherical resonator PAS systems.
• Attained 223 parts-per-trillion (ppt) detection limit for C2H2.
• Achieved a normalized noise equivalent absorption coefficient of 9.8 × 10^-10 cm^-1 W/Hz^1/2.

Conclusions:

• The novel dual-enhancement fiber-optic PAS sensor resolves the trade-off between structural integrity and detection sensitivity in spherical resonators.
• The proposed sensor offers a compact, all-optical, and robust solution for ultrasensitive gas detection.
• This technology holds significant promise for applications in complex or harsh environments.