Photothermal Gas Detection With a Dithered Low-Finesse Fiber-Optic Fabry-Pérot Interferometer

Chenyu Yao, Shoulin Jiang, Shoufei Gao, Yingying Wang, Wei Jin, Wei Ren

Research output: Journal article publicationJournal articleAcademic researchpeer-review

4 Citations (Scopus)


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 languageEnglish
Article number9924575
Pages (from-to)745-751
Number of pages7
JournalJournal of Lightwave Technology
Issue number2
Publication statusPublished - 15 Jan 2023


  • Fabry-Parot interferometer
  • gas sensing
  • hollow-core fiber
  • photothermal spectroscopy

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics


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