Abstract
Pump-probe photothermal spectroscopy has been recently proposed for sensitive gas detection. The probe laser wavelength was usually locked at the quadrature point of an interferometer to provide a linear output of the phase signal. However, this detection scheme brings unwanted fluctuations to the interferometer. Here we report a novel phase demodulation method of the probe laser for photothermal spectroscopy to enhance the stability. We demonstrate a proof-of-concept experiment by performing photothermal detection of methane (CH4) inside a hollow-core fiber, which is sandwiched by two pieces of solid-core fibers to form a low-finesse fiber-optic Fabry-Pérot interferometer (FPI). Besides the wavelength modulation of the 1.65-μm pump laser, we employed a dither to modulate the injection current of the probe diode laser, which was frequency-locked to the FP cavity resonance. The photothermal signal was sensitively measured from the error signal of the feedback loop by demodulating the FPI output at the dither frequency. A normalized noise equivalent absorption (NNEA) coefficient of 7.5 × 10-9 cm-1WHz-1/2 was achieved in this work. A comparison to the conventional quadrature point locking technique was performed to reveal the remarkable sensor stability with immunity to optical disturbance.
Original language | English |
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Article number | 9924575 |
Pages (from-to) | 745-751 |
Number of pages | 7 |
Journal | Journal of Lightwave Technology |
Volume | 41 |
Issue number | 2 |
DOIs | |
Publication status | Published - 15 Jan 2023 |
Keywords
- Fabry-Parot interferometer
- gas sensing
- hollow-core fiber
- photothermal spectroscopy
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics