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The Letter reports what the authors believe to be the first single-wavelength pumped, CW, room-temperature, blue upconversion laser. This 480nm laser uses Tm3+ as the active ion in a fluorozirconate glass fibre. Up to 60 mW of output power has been observed with a slope efficiency of 18% with respect to coupled pump power.
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Grubb et al. (1992) studied this question.
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