Mid-infrared sources, based on chalcogenide glass fibres, for biomedical diagnostics

Mid-infrared (MIR) direct fiber lasers beyond 4 μm wavelength will deliver optimum beam quality of bright, spatially and temporally coherent light, routeable in MIR fiber-optics. They are being developed for applications including narrow-band biomolecular sensing, medical laser surgery at new, long wavelengths and for pulsed seeding of long wavelength MIR-supercontinua in MIR glass fiber for all-fiber, compact systems for broad-band MIR medical sensing and hyperspectral imaging. Low phonon energy, selenide chalcogenide glasses are the optimum glass host for lanthanide ion doping for emission across the 3 to 10 μm wavelength MIR region. Here, we report our recent advances including: >1 mW incoherent emission in the 4-5 μm wavelength region and demonstration of gain beyond 4 μm in Pr3+ doped chalcogenide glass fiber, and proposed quasi three-level lasing beyond 4 μm in Tb3+ doped chalcogenide glass fibers. Encouragingly, since 2020, lasing in both Pr3+ and Tb3+ selenide chalcogenide bulk glasses has been reported. Our overall goal is for new portable, MIR spectroscopic systems based on chalcogenide optical fibers for in vivo sensing, imaging and treatment in healthcare, including for early diagnosis of disease.