Although erbium (Er)-doped zirconium barium lanthanide sodium fluoride (ZBLAN) lasers have achieved power levels around 2 W, these levels are not sufficient to enable their use as mid-infrared (IR) Raman lasers, laser scalpels with high ablation efficiency and micrometer resolution, or terahertz local oscillators. However, researchers at the University of New Mexico (Albuquerque, NM) have developed a mid-IR ZBLAN fiber laser with over 9 W continuous-wave output power that could move these applications from research to reality.
To achieve this power increase, the natural population-inversion bottleneck caused by the longer lifetime of the lower laser level relative to the upper laser level for the Er atoms was overcome by using a heavily Er-doped ZBLAN double-clad fiber. A technique called energy-transfer upconversion was used, in which an energy-transfer process between Er ions solves the population bottleneck and increases the output power. Slope efficiencies of 21% were obtained at power levels of greater than 9 W; however, the damage threshold of the fiber would need to be increased to achieve even higher output power levels. Contact Xiushan Zhu at [email protected].