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Synthesis and Operation of Fluorescent-core Microcavities for Refractometric Sensing
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Published on: March 13, 2013

Cavity ring down spectroscopy with 5 × 10(-13) cm-1 sensitivity.

Samir Kassi1, Alain Campargue

  • 1Laboratoire Interdisciplinaire de Physique, CNRS UMR 5588, Université Joseph Fourier de Grenoble B.P. 87, 38402 Saint-Martin d'Hères Cedex, France. Samir.Kassi@ujf-grenoble.fr

The Journal of Chemical Physics
|December 27, 2012
PubMed
Summary

Continuous wave-cavity ring down spectroscopy achieved high sensitivity for detecting weak molecular transitions. Averaging over days improved detection limits to 5 × 10(-13) cm(-1), enabling observation of ultra-weak oxygen and nitrogen spectral lines.

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Area of Science:

  • Spectroscopy
  • Molecular Physics
  • Chemical Sensing

Background:

  • Cavity Ring Down Spectroscopy (CRDS) is a powerful technique for high-sensitivity absorption measurements.
  • Achieving ultimate sensitivity in CRDS is often limited by detector noise and baseline fluctuations.
  • Investigating weak molecular transitions requires highly sensitive spectroscopic methods.

Purpose of the Study:

  • To investigate the ultimate sensitivity performances of a continuous wave-cavity ring down spectroscopy (CW-CRDS) setup in the near-infrared region.
  • To identify and overcome limitations affecting detection sensitivity.
  • To demonstrate the achieved sensitivity by detecting weak molecular absorption lines.

Main Methods:

  • Utilized a continuous wave-cavity ring down spectroscopy (CW-CRDS) setup operating in the near-infrared spectrum.
  • Analyzed noise sources, particularly photodetector noise, at fixed frequencies.
  • Implemented long-term averaging techniques to mitigate baseline drift and improve signal-to-noise ratio.

Main Results:

  • At fixed frequencies, photodetector noise was the primary limitation, yielding a detection limit of approximately 10(-11) cm(-1) after 10 s averaging.
  • Long-term averaging over several days significantly reduced baseline fluctuations, achieving a detection limit as low as 5 × 10(-13) cm(-1).
  • Successfully observed ultra-weak transitions of the oxygen (¹⁶O₂) a(1)Δg(0)-X (3)Σg⁻(1) hot band near 1.58 μm and the first detection of an electric quadrupole transition in nitrogen ((14)N₂) near 1.44 μm.

Conclusions:

  • CW-CRDS can achieve remarkable sensitivity, particularly when long-term averaging is employed to overcome baseline instabilities.
  • The demonstrated sensitivity enables the study of extremely weak molecular absorption features previously inaccessible.
  • This work highlights the potential of CRDS for high-precision molecular spectroscopy and trace gas detection.