Abstract
Thanks to the guidance of an optical wave in air, hollow-core fibers may serve as sampling cells in an optical spectroscopic system. This paper reviews applications of hollow-core optical fibers to laser-based gas sensing. Three types of hollow-core fibers are discussed: Hollow capillary waveguides, photonic band-gap fibers, and negative curvature fibers. Their advantages and drawbacks when used for laser-based trace gas detection are analyzed. Various examples of experimental sensing systems demonstrated in the literature over the past 20 years are discussed.
Highlights
Laser spectroscopy has become a powerful tool in trace gas detection with a variety of applications, including environmental monitoring, breath analysis, industrial process monitoring, and leak detection
Optical systems operating in the infrared region may be equipped with thermo-electrically cooled (TEC) detectors and reliable and robust semiconductor sources, which enables out-of-lab operations with minimal maintenance
This paper summarizes the examples of using hollow-core fibers for trace gas detection in the nearand mid-infrared spectral regions
Summary
Laser spectroscopy has become a powerful tool in trace gas detection with a variety of applications, including environmental monitoring, breath analysis, industrial process monitoring, and leak detection. This process is governed by the Beer–Lambert law:. Where I0 and I are the light intensities before and after the sample, respectively; L is the interaction length; σ is the absorption cross-section; and N is the number density (concentration). One can deduce the molecular concentration by measuring the decay of the intensity after the light beam has passed through the sample (assuming that the interaction length and the absorption cross-section are known)
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