Tb-doped Materials for Visible Lasers

Terbium (Tb) doped materials are potential laser gain media for achieving high pulse energy in the visible region. It features long upper level life time, high quantum efficiency, and large energy storage capability. There were only intermittent studies on Tb lasers since its first demonstration in 1967 [1] , [2] . Recently, research has been activated by two major advances that have influenced this subject. In 2007, Yamashita et al., demonstrated the first continuous wave oscillation of Tb laser with Tb doped ZBLAN fiber [3] . Ten years later from this achievement, Kränkel's group succeeded in highly efficient continuous oscillation of a Tb laser using a Tb doped fluoride single crystal [4] . Based on these results, our group demonstrated the first Q-switched oscillation of Tb laser [5] . It takes around 50 years from the first laser oscillation of Tb laser. This is because of the improvements and investigations of Tb doped laser gain medium and the development of the excitation light sources emitting around 488 nm such as optically pumped semiconductor lasers or blue laser diodes. Now we focus on the high Tb concentrated gain medium of LiTbF 4 (TLF). One of the disadvantages of Tb 3+ doped material is its low absorption coefficient at main pumping wavelength of 488 nm. High Tb 3+ concentrated material can overcome this disadvantages.