Role of pump duration on temperature and efficiency of up-conversion in fluoride crystals co-doped with ytterbium and thulium

Pump pulse duration is shown to determine the maximum efficiency of the up conversion process in ytterbium, thulium co-doped fluoride crystals through its role in determining the emitter temperature reached. We show that up-conversion efficiencies should only be measured when using the same pumping conditions as would be used in a proposed application and that thermal management of the up converting material is critical to optimized performance.