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.
Highlights
LASER excited photoacoustic spectroscopy (PAS) has been used as a tool for trace gas detection with high sensitivity and gas species selectivity in a large number of application fields ranging from medical diagnostics [1], industrial process control [2] and gas leak detection [3] to environmentalManuscript received February 16, 2015
We present the novel application of a custom Raman fiber amplifier as the source for a fiber coupled miniaturized 3D printed PAS trace gas sensor
We have presented the development of a counter-propagating Raman amplifier system at 1651 nm and its application as a source for miniaturized 3D printed PAS trace gas sensing of CH4
Summary
LASER excited photoacoustic spectroscopy (PAS) has been used as a tool for trace gas detection with high sensitivity and gas species selectivity in a large number of application fields ranging from medical diagnostics [1], industrial process control [2] and gas leak detection [3] to environmental. The Raman fiber amplifier is tailored for signals at 1651 nm for the interrogation of methane absorption lines and has an output power above 1W and a frequency modulation scheme to suppress SBS This technique can be applied with a variety of seed laser and pump combinations for detection of a vast number of further trace gases (e.g. H2O2, CO, CO2, N2O). The miniaturization advantage of PAS gas sensors, targeted through the miniaturized 3D printed format in this work, can be derived from (1) when the dimensional parameters influencing the Q-factor and the cell resonance frequency are included [36] This leads to a pressure signal dependency of [8]: II. The resulting first longitudinal resonance frequency was simulated as 15.3 kHz, with its maximum acoustic pressure located at the microphone position
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