*Review* **A Review of Antiresonant Hollow-Core Fiber-Assisted Spectroscopy of Gases**

**Piotr Jaworski**

Laser and Fiber Electronics Group, Faculty of Electronics, Wroclaw University of Science and Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland; piotr.jaworski@pwr.edu.pl

**Abstract:** Antiresonant Hollow-Core Fibers (ARHCFs), thanks to the excellent capability of guiding light in an air core with low loss over a very broad spectral range, have attracted significant attention of researchers worldwide who especially focus their work on laser-based spectroscopy of gaseous substances. It was shown that the ARHCFs can be used as low-volume, non-complex, and versatile gas absorption cells forming the sensing path length in the sensor, thus serving as a promising alternative to commonly used bulk optics-based configurations. The ARHCF-aided sensors proved to deliver high sensitivity and long-term stability, which justifies their suitability for this particular application. In this review, the recent progress in laser-based gas sensors aided with ARHCFs combined with various laser-based spectroscopy techniques is discussed and summarized.

**Keywords:** antiresonant hollow core fibers; laser spectroscopy; wavelength modulation spectroscopy; tunable diode laser absorption spectroscopy; photothermal spectroscopy; photoacoustic spectroscopy; fiber gas sensors

**Citation:** Jaworski, P. A Review of Antiresonant Hollow-Core Fiber-Assisted Spectroscopy of Gases. *Sensors* **2021**, *21*, 5640. https:// doi.org/10.3390/s21165640

Academic Editor: Bernhard Wilhelm Roth

Received: 29 July 2021 Accepted: 19 August 2021 Published: 21 August 2021

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