Fiber-Tip Gas Transducer Based on All-Optical Photoacoustic Spectroscopy

In this paper, a fiber-tip all-optical photoacoustic (PA) transducer is demonstrated. The transducer is integrated by a silicon cantilever, a single optical fiber and a silicon dioxide tube. The excitation light source of the PA signals and the detecting light source of the Fabry-Perot (F-P) fiber-optic acoustic transducer are coupled in a single fiber through a wavelength division multiplexer. The silicon dioxide tube has a truncated cone-shaped cavity, which serves both as the F-P cavity and PA cell. Due to this special structure, the volume of the PA cell is ∼ 1.1 μL and the overall volume of the transducer is ∼ 17 cubic millimeters. The miniaturized transducer, combines with a near infrared distributed feedback laser together with a high-speed spectrometer constitutes a PA spectroscopy (PAS) system for methane detection. With an averaging time of 100 s, the minimum detection limit is extrapolated to be 5.2 parts-per-million and the normalized noise equivalent absorption is obtained to be 4.58 × 10
⁻⁷
cm
⁻¹
WHz
^−1/2
. The proposed transducer is completely suitable for remote, long-distance as well as limited-space trace gas detection.