Hollow-core fiber Fabry-Pérot photothermal gas sensing characteristics over the temperature range of 256–354K

We study the temperature dependance of photothermal signal in a hollow-core fiber (HCF) Fabry-Perot photothermal gas sensor. The photothermal signal generally increases with decreasing temperature, due to the temperature dependent absorption and thermal properties of the gas sample in the hollow-core. The temperature variation also changes the cavity length of the Fabry-Perot, which results in pump power fluctuation in the cavity due to multi-path interference and hence the photothermal signal. This fluctuation can be reduced considerably by applying proper modulation to the pump wavelength. With an 11-cm-long HCF gas cell, we demonstrated a detection limit of ~ 6 ppb acetylene in nitrogen with a 1 s lock-in time constant. With a simple temperature compensation scheme, the photothermal signal fluctuation can be reduced from 48% to 2% over the temperature range of 256–354 K.