4.8-μm CO-filled hollow-core silica fibre laser

Abstract

Mid-infrared (MIR) fibre lasers are important for a wide range of applications in sensing, spectroscopy, imaging, defense, and security. Some progress has been made in the research of MIR fibre lasers based on soft glass fibres, however, the emission range of rare-earth ions and the robustness of the host materials are still a major challenge for MIR fibre lasers. The large number of gases provide a variety of optical transitions in the MIR band. When combined with recent advances in low-loss hollow-core fibre (HCF), there is a great opportunity for gas-filled fibre lasers to further extend the radiation to the MIR region. Here, a 4.8-µm CO-filled silica-based HCF laser is reported for the first time. This is enabled by a homemade broadband low-loss HCF with a measured loss of 1.81 dB/m at 4.8 µm. A maximum MIR output power of 46 mW and a tuning range of 180 nm (from 4644 to 4824 nm) are obtained by using an advanced 2.33-µm narrow-linewidth fibre laser. This demonstration represents the longest-wavelength silica-based fibre laser to date, while the absorption loss of bulk silica at 4824 nm is up to 13, 000 dB/m. Further wavelength expansion could be achieved simply by changing the pump absorption line. This work paves the way for the MIR silica fibre laser beyond 5 µm.