Pulsed photothermal interferometry for high sensitivity gas detection with hollow-core photonic bandgap fibre

Abstract

Pulsed photothermal interferometry (PTI) gas sensor with hollow-core photonic bandgap fibre (HC-PBF) is demonstrated with a Sagnac interferometer-based phase detection system. Under the condition of constant peak pump power, the optimal pulse duration is found to be > 1:2 μs for detecting low-concentration of trace gases in nitrogen, limited by thermal conduction of gases within the hollow-core. Preliminary experiments with a 0.62-mlong HC-PBF gas cell, low peak power ( ~ 20:2mW) and a boxcar averager with 10k average times demonstrated a detection limit of 3:3 p:p:m acetylene. Detection limit down to ppb or lower is expected with high peak power pump pulses.