Strong C-H bond absorption , and moderate water absorption in the spectral region around ~1.7 μm make this wavelength band of interest for a range of applications, including polymer processing and laser surgery . Despite being a growing area of interest, development of high-power laser sources in this region has been limited. Daniel et al , showed that high-power, continuous-wave generation between 1.66 - 1.75 μm could be achieved by in-band pumping thulium-doped fibre (TDF) at 1565 nm using an erbium/ytterbium co-doped (Er/Yb) fibre laser, displaying 12.6 W at 1726 nm. Yb is added as a co-dopant to Er-doped fibres (EDF) to increase pump absorption efficiency. However, parasitic lasing in the Yb emission band at 1 μm can limit efficiency and the onset of self-pulsing can cause catastrophic damage, limiting single-mode output power and operating lifetimes. Here we report the use of a cladding-pumped Er-only fibre laser (EDFL) to core pump a thulium-doped fibre laser (TDFL), efficiently generating >25 W of single-mode output at 1726 nm.
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