Efficient Tm-doped silica fiber laser incorporating nanoparticle doping

This study reports the efficient operation of a first-in-class Tm-doped aluminosilicate fiber laser, in which the fiber incorporates nanoparticle doping of the Tm ions. This approach enables relatively high localized Tm-doping concentrations to be realized that greatly exceed the normal doping levels achieved using standard solution doping methods. Two fibers were produced, with different Tm concentrations within the nanoparticles (20 mol.% and 100 mol.%) that also had different nanoparticle doping levels in the cores. The diode-pumped fiber lasers produced moderately high slope efficiencies >50%, providing evidence that the 'two-for-one' cross-relaxation process is being exploited, while maintaining a modest increase in core refractive index and numerical apertures (NAs) around 0.15. The values of quantum efficiency achieved were 1.35 and 1.53 for the 20 mol.% Tm:NP and 100 mol.% Tm:NP fibers, respectively. There is evidence that energy transfer upconversion may be impacting the laser performance, however this cannot be adequately quantified in this current study. The core propagation loss in the two-micron band was determined to be 0.14 dB/m and 0.42 dB/m for the the 20 mol.% Tm:NP and 100 mol.% Tm:NP fibers, respectively. Crucially, this parameter is significantly higher than our estimated contribution from Rayleigh scattering and scaled with the spatially-averaged Tm-doping concentration, rather than the NP concentration.