LD-seeded thulium-doped fibre amplifier for CO2 measurements at 2 µm

Carbon dioxide (CO2) measurements are of interest to the aviation industry because of the need to reduce net CO2 emission from aero (“jet”) engines [1] as well as for engine diagnostics. Chemical Species Tomography (CST) is a technique that uses an optical source for multi-path integrated absorption measurements and from those calculates a 2-dimensional image of target gas concentration [2]. In FLITES [3], we target CST of CO2 in aero-engine exhaust plumes with diameter up to ~ 1.4 m at wavelengths around 2 μm. Typically, single-path absorption measurements are carried out using distributed feedback (DFB) diode lasers with powers of ~2 mW. For CST, however, it would be necessary to use over one hundred separate paths, and thus laser sources, to achieve adequate spatial and temporal resolution. It is essential that a single CST-capable laser source, with total power above 1 W, is developed and the light distributed into the individual paths using optical fibre components.