The mid-IR wavelength range, and the fundamental vibrational absorption fingerprint region it encompasses, can be utilised for a variety of environmental and medical monitoring applications requiring the detection of specific covalently bonded molecules, for example, in atmosphere or in a patient’s breath. Mid-IR transmitting chalcogenide fibres, based on the elements: sulfur, selenium, and tellurium, have a characteristically high optical non-linearity and thus can be tailored to also generate mid-IR supercontinuum light that covers this fingerprint region.
The process of designing, fabricating, and characterising chalcogenide glass fibres via differential scanning calorimetry, microscopy, ellipsometry, and optical fibre loss measurements is detailed.
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.
Many important molecules show strong characteristic vibrational transitions in the mid-infrared (MIR) part of the electromagnetic spectrum. This leads to applications in spectroscopy, chemical and bio-molecular sensing, security and industry, especially over the mid- and long- wave infrared atmospheric transmission windows of 3-5 μm and 8-13 μm. In this paper, we review some of our more recent experimental and simulation work aimed at developing new light sources based on chalcogenide glass optical fibres that can help us utilize this spectral region for biomedical applications. This includes the development of supercontinuum and bright luminescent sources and our progress towards fibre-based lasers. We place these developments in the context of MIR imaging and spectroscopy in order to show how they bring the promise a new era in healthcare and clinical diagnostics.
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