Miniaturized Photoacoustic Trace Gas Sensing Using a Raman Fiber Amplifier

Abstract

This paper presents the development of a Raman fiber amplifier optical source with a maximum output power of 1.1 W centered around 1651 nm, and its application in miniaturized 3D printed photoacoustic spectroscopy (PAS) trace gas sensing of methane. The Raman amplifier has been constructed using 4.5 km of dispersion shifted fiber, a 1651 nm DFB seed laser and a commercial 4W EDFA pump. The suppression of stimulated Brillouin scattering (SBS) using a high frequency modulation of the seed laser is investigated for a range of frequencies, leading to an increase in optical output power of the amplifier and reduction of its noise content. The amplifier output was used as the source for a miniature PAS sensor by applying a second modulation to the seed laser at the resonant frequency of 15.2 kHz of the miniature 3D printed gas cell. For the targeted methane absorption line at 6057 cm -1 the sensor system performance and influence of the SBS suppression is characterized, leading to a detection limit (1σ) of 17 ppb methane for a signal acquisition time of 130 s, with a normalized noise equivalent absorption coefficient of 4.1·10 -9 cm -1 W Hz -1/2 for the system.Index Terms-Miniaturized fiber optic sensor, 3D printed photoacoustic trace gas sensor, Raman fiber amplifier system, SBS suppression

Performance of a Azimuthally excited 3D-printed resonator for multi-pass spectroscopic applications

“…The excitation of the azimuthal modes provides a much higher Q-factor compared to other 3D-printed cells which are designed for longitudinal excitation [5], [6], for which Qfactors of approximately 15 have been reported. A further advantage of azimuthal excitation is the presence of an antinode at the bottom of the cell.…”

“…A wide range of resonant cell designs have been investigated [4], aimed at exciting either the longitudinal, azimuthal, or radial modes with the clear majority of designs exciting the longitudinal resonant mode . Previously, we have presented the development of medium to low Q-factor cells which can be rapidly manufactured using a photo-polymerisation based 3D-priniting technique [5], [6].…”

Advances in Mid-Infrared Spectroscopy-Based Sensing Techniques for Exhaled Breath Diagnostics

“…Bauer et al presented the development of a Raman amplifier system operating at 1651 nm and its application for trace gas sensing with a miniaturized 3D printed PAS cell. The system exhibited high sensitivity towards methane sensing with the least detection limit of 17 ppb at a signal acquisition time of 130 s [116].…”

Operation of a Single-Frequency Bismuth-Doped Fiber Power Amplifier near 1.65 µm

“…However, because these wavelengths are at the edge of the thulium gain band, the highest demonstrated saturation power near 1650 nm was less than 50 mW [7,8]. Raman amplifiers are capable of providing much higher output powers, but require long (about 1 km or more) pieces of specialty fiber [9] and very high (watt level) pumping powers [10]. In this respect, bismuth-doped fiber amplifiers are interesting alternatives that may be used to obtain decent output powers (beyond 100 mW) in a simple and compact configuration, similar to rare earth-doped amplifiers.…”