Energy level calculations for rare-earth doped fluoride glasses

Summary form only given. Rare-earth doped glasses are used for many applications such as glass and fiber lasers and fiber amplifiers. In the field of active fiber applications, fluoride fibers are of special interest, because most optical transitions in the rich energy level system of rare-earth ions cannot be used in usual silica fibers. Because of their low maximum phonon energy around 500-600 cm^-1, fluoride fibers allow fiber lasers in the mid-infrared up to 3.9 μm, and fiber amplifiers in the near infrared for new transmission windows and visible fiber lasers pumped by the usual NIR laser diodes. In contrast to transition metal ions, rare-earth ions keep the line structure of their energy level system even in solid state materials, due to the weak interaction of the optical active electrons with the glass matrix. Although the position of the energy levels is relatively independent of the specific glass matrix, this is not the case for the strength of the transitions, which is important for the laser characteristics. We present measurements and calculations of important spectroscopic parameters for Pr³⁺ and Tm³⁺ as dopands in zirconium - and in indium-based fluoride glasses, which are the most important families of fluoride glasses.