Kagome Hollow Core Fiber-Based Mid-Infrared Dispersion Spectroscopy of Methane at Sub-ppm Levels.

Karol Krzempek,Michal Nikodem,Krzysztof Abramski

doi:10.3390/s19153352

Abstract

In this paper, we demonstrate the laser-based gas sensing of methane near 3.3 µm inside hollow-core photonic crystal fibers. We exploit a novel anti-resonant Kagome-type hollow-core fiber with a large core diameter (more than 100 µm) which results in gas filling times of less than 10 s for 1.3-m-long fibers. Using a difference frequency generation source and chirped laser dispersion spectroscopy technique, methane sensing with sub-parts-per-million by volume detection limit is performed. The detection of ambient methane is also demonstrated. The presented results indicate the feasibility of using a hollow-core fiber for increasing the path-length and improving the sensitivity of the mid-infrared gas sensors.

Highlights

Infrared laser spectroscopy is a sensitive and selective technology with a number of practical applications
Examples of laser spectroscopy using long capillary with reflective inner coating were presented in [7,8]. When this type of fiber is used for gas sensing, multimode propagation or scattering on inner surfaces may occur, possibly leading to the presence of optical fringes which strongly limit the performance when standard absorption-based methods are used
Coherent mid-infrared light was obtained through the difference frequency generation process in a periodically poled lithium niobate (PPLN)

Summary

Introduction

Infrared laser spectroscopy is a sensitive and selective technology with a number of practical applications. The simplest and frequently used solution for further improvement of the minimum detection limit (MDL) is to increase the sensing path-length using multi-pass cells. This approach typically leads to sensitivities at parts-per-million or parts-per-billion by volume levels (ppmv and ppbv, respectively) [1,2,3,4,5]. Examples of laser spectroscopy using long capillary with reflective inner coating were presented in [7,8] When this type of fiber is used for gas sensing, multimode propagation or scattering on inner surfaces may occur, possibly leading to the presence of optical fringes which strongly limit the performance when standard absorption-based methods (such as tunable diode laser absorption spectroscopy or wavelength modulation spectroscopy) are used. Similar limitations are observed in the configuration incorporating photonic bandgap (PBG)

Methods

Results

Conclusion