This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The goal of this project is to develop a solid state laser that produces visible output wavelengths, including the commercially compelling blue wavelength. The basic architecture of the device consists of a single-mode optical fiber doped with Pr{sup 3+} and Yb{sup 3+} ions. When the ions are simultaneously pumped with a near infrared laser (860 nm), complex energy transfer processes involving multiple excited ions leads to population of a high-lying energy level of Pr{sup 3+}. Results include the demonstration of the existence of a photon avalanche mechanism responsible for creation of the population inversion and demonstration of the highest optical-to-optical efficiency of any up-conversion laser reported to date. A US Patent was awarded for this invention in 1998.