New pumping schemes for the Tm-doped ZBLAN blue upconversion fiber laser operating at 455 nm

re present a model for a 455 nm thulium-doped ZBLAN fiber laser co-pumped at 645, 684 and 1064 nm. This model calculates the blue laser output power using a rate equation analysis and takes into account the cross-relaxation and cooperative upconversion processes. We calculate the optimal pump wavelength for the case of a single visible pump wavelength, and then show the benefits of adding the second visible pump wavelength at 684 nm for a low 1064 nm pump power (120 mW). At high infrared pump powers (≥600 mW), we then show that adding the second pump does not increase the efficiency of the laser. These results are explained by studying the population densities of the energy levels of the thulium ions for each pumping configuration.