Cavity-Enhanced Photothermal Gas Detection With a Hollow Fiber Fabry-Perot Absorption Cell

A photothermal (PT) gas sensor with a hollow-core photonic bandgap fiber (HC-PBF) Fabry-Perot absorption cell is demonstrated. The formation of a high finesse cavity enhances the pump intensity and hence PT phase modulation as well as the sensitivity of PT phase detection by a factor that is proportional to the cavity finesse. Experiments with a 6.2-cm long HC-PBF absorption cell with a finesse of 45 for the pump and 41 for the probe demonstrated detection of 100 part-per-million acetylene in nitrogen with a signal-to-noise ratio of 795 for a detection bandwidth of 0.031 Hz. The double-cavity-enhanced PT gas sensor allows the use of a shorter HC-PBF to develop highly sensitive and fast all-fiber gas sensors.