Mid-infrared fiber lasers at and beyond 3.5 μm using dual-wavelength pumping.

We report the first, to the best of our knowledge, erbium-doped zirconium-fluoride-based glass fiber laser operating well beyond 3 μm with significant power. This fiber laser achieved 260 mW in CW at room temperature. The use of two different wavelength pump sources allows us to take advantage of the long-lived excited states that would normally cause a bottleneck, and this enables maximum incident optical-to-optical efficiency of 16% with respect to the total incident pump power. Both output power and efficiency are an order of magnitude improvement over similar lasers demonstrated previously. The fiber laser operating at 3.604 μm also exhibited the longest wavelength of operation obtained to date for a room temperature, nonsupercontinuum fiber laser.