Spectroscopy of Ho3+-doped fluoride glasses for green double-clad fiber lasers

Oxxius green fiber laser research today

Published in SPIE Fiber Lasers and Glass Photonics in 2022, this paper provides the first systematic spectroscopic assessment of Ho:ZBLAN green fiber laser materials at 549 nm — characterizing absorption and stimulated-emission cross-sections, luminescence lifetimes, and concentration quenching across a range of HoF₃ doping levels in ZBLAN glass. The results are used to simulate the output performance of a diode-pumped double-clad fiber laser geometry, identifying the optimal doping concentration and fiber parameters for efficient green emission.

Holmium-doped ZBLAN glass is a compelling candidate for green fiber lasers because its ⁵F₄+⁵S₂ → ⁵I₈ transition near 549 nm is efficiently pumped by 448–450 nm GaN blue diodes — the same pump wavelength used in the Dy:ZBLAN yellow laser work published by the same group. The absorption cross-section measured here (1.75×10⁻²⁰ cm² at 448.5 nm) and the stimulated-emission cross-section (0.67×10⁻²⁰ cm² at 549 nm) provide the material parameters needed to design practical Ho:ZBLAN fiber laser systems with predictable performance.

Green lasers for life science instrumentation

The 549 nm wavelength sits adjacent to the widely used 532 nm and 561 nm lines, and within the optimal excitation range for several green-yellow fluorophores including TRITC and Cy3. A compact, all-fiber green source at 549 nm pumped by a GaN diode would offer a vibration-insensitive, alignment-free alternative to DPSS lasers for microscopy and flow cytometry. This spectroscopic groundwork, combined with Oxxius’s expertise in high-brightness GaN diode modules, positions the LBX-450 as the natural pump source for future Ho:ZBLAN green fiber laser demonstrations.

Abstract

Holmium ions (Ho3+) are attractive for generation of green emission according to the 5F4+ 5S2 → 5 I8 transition. We report on the assessment of the potential of Ho3+ -doped fluoride glasses for green fiber lasers exploiting the double-clad fiber geometry. ZBLAN glasses doped with HoF3 (0.1 – 0.9 mol%) were studied. The absorption cross-section for the 5 I8 → 5F1+ 5G6 transition is 1.75×10-20 cm2 at 448.5 nm. Under excitation in the blue, the glasses exhibit intense green luminescence. The stimulated-emission cross-section for the 5F4+ 5S2 → 5 I8 transition is 0.67×10-20 cm2 at 549 nm. With increasing the HoF3 doping level, the luminescence lifetime of the 5F4+ 5S2 states slowly decreases in the range of 291 – 180 μs. The output performance of a diode-pumped green Ho fiber laser was simulated for a fiber geometry with a double D-shaped inner cladding. The variable parameters were the HoF3 doping …