Mid-infrared supercontinuum sources have attracted much attention as they offer high power densities over a broad bandwidth and are therefore deemed suitable for a range of spectroscopy-related applications. The 1–4 μm spectral range is easily covered by fibres made from fluoride glasses (such as ZBLAN) or telluride. Now, an international collaboration between universities and companies from Denmark, Germany and the UK has explored theoretically the possibility to extend emission to much longer wavelengths by employing chalcogenide step-index fibres, based on As-Se/Ge-As-Se (core/cladding) glasses, pumped by a Pr3+-doped fibre laser (4 MHz repetition rate, 50 ps pulse width). Design simulations revealed that fibres with a numerical aperture (NA) of 1 and a core diameter of 10 μm were able to generate a flat spectrum up to 10.7 μm in wavelength and operation could be extended to 12.5 μm by reducing the core diameter to 8 μm. However, for larger diameter (20 μm or more) fibres with a NA between 0.5 and 1, lower nonlinearity required pumping at higher powers (∼4.7 kW) to generate a supercontinuum out to 10.6 μm. This latter scheme may prove useful for designing fibres that can handle higher power densities.
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Maragkou, M. Reaching the mid-infrared. Nature Photon 8, 746 (2014). https://doi.org/10.1038/nphoton.2014.231