Nigel C. Neate

Mid-infrared photoluminescence in small-core fiber of praseodymium-ion doped selenide-based chalcogenide glass

Rare earth (RE)-ion doped chalcogenide glasses are attractive for mid-infrared (MIR) fiber lasers for operation >4 μm. Our prior modeling suggests that praseodymium (Pr) is a suitable RE-ion dopant for realizing a selenide-based, chalcogenide-glass, step index fiber (SIF) MIR fiber laser operating at 4-5 μm wavelength. Fabrication of RE-ion doped chalcogenide glass fiber, especially with a small core, is a demanding process because crystallization must be avoided during the heat treatments required to effect shaping. Here, a 500 ppmw (parts per million parts, by weight) Pr3+-doped Ge-As-Ga-Se glass SIF with a 10 μm or 15 μm diameter core is reported; the cladding glass is Ge-As-Ga-Se-S. The multistage process to produce the fiber is outlined. Thermal and optical properties of the core/clad. glass pair, and the crystalline/amorphous nature and optical behavior of the small core fiber are reported. MIR photoluminescence and lifetime of a RE-ion doped chalcogenide glass small core fiber are reported for the first time.

Toward Mid-Infrared, Subdiffraction, Spectral-Mapping of Human Cells and Tissue: SNIM (Scanning Near-Field Infrared Microscopy) Tip Fabrication

Scanning near-field infrared microscopy (SNIM) potentially enables subdiffraction, broadband mid-infrared (MIR: 3-25-μm wavelength range) spectral-mapping of human cells and tissue for real-time molecular sensing, with prospective use in disease diagnosis. SNIM requires an MIR-transmitting tip of small aperture for photon collection. Here, chalcogenide-glass optical-fibers are reproducibly tapered at one end to form a MIR-transmitting tip for SNIM. A wet-etching method is used to form the tip. The tapering sides of the tip are Al-coated. These Al-coated tapered-tips exhibit near-field power-confinement when acting either as the launch-end or exit-end of the MIR optical fiber. We report first time optimal cleaving of the end of the tapered tip using focused ion beam milling. A flat aperture is produced at the end of the tip, which is orthogonal to the fiber-axis and of controlled diameter. A FIB-cleaved aperture is used to collect MIR spectra of cells mounted on a transflection plate, under illumination of a synchrotron-generated wideband MIR beam.

The local environment of Dy3+in selenium-rich chalcogenide glasses

The environment of Dy3+ is investigated when it is added as DyCl3 or Dy foil into two base glasses, Ge16.5As19−xGaxSe64.5, where x = 3 or 10 at%, at doping levels between 0 and 3000 parts per million by weight (ppmw) Dy3+. Extended X-ray Absorption Fine Structure demonstrates the glasses doped with Dy foil, or less than 1000 ppmw Dy3+ as DyCl3, contain Dy ions that are fully incorporated into the glass network and are coordinated by 7–8 Se atoms. However, when the DyCl3 dopant is present in concentrations ≥1000 ppmw Dy3+ the environment is dominated by Dy–Cl bonds. Furthermore, these Dy–Cl environments are nanocrystalline, retaining chemical order beyond the first coordination shell. By comparison with XRD and FTIR results, we report that the presence of α-Ga2Se3 crystallites in the glass, and the increased optical scattering in the fibres, are both related to the presence of DyCl3 crystallites.