Femtosecond mode-locked Yb3+-doped CaFi-LaFs ceramic laser

In recent years, Yb
³⁺
doped calcium fluoride (Yb:CaF2) has attracted great attention as a gain media for ultrashort pulse laser oscillator and amplifier. Yb:CaF2 has many advantages suitable for mode locked laser e.g. very broad and smooth fluorescence spectrum shape, relatively high thermal conductivity, and long fluorescence lifetime [1]. Especially, its fluorescence spectrum bandwidth of about 70 nm is much broader than other typical broad gain media and comparable with Yb:CALGO. Such broad spectrum bandwidth helps significant pulse shortening of ultrashort pulse laser. In addition, the relatively higher thermal conductivity of 9.7 W/mK (non-dope) is suitable for high power operation. Thanks to those advantages, Yb:CaF2 has already shown very good results as mode-locked laser, ultrashort pulse amplifier and thin disk laser. But all of those reports were based on Yb: CaF2 single crystals and Yb: CaF2 ceramic is under development. Transparent ceramics have many advantages for high power laser gain media. Hence recently fabrication of rare-earth doped CaF2 ceramics have been tried extensively [2-4]. In this paper, we report the first mode-locked operation using Yb
³⁺
-doped CaF2 ceramic based material, Yb
³⁺
-doped CaF2-LaF3 ceramic as a gain media. Our ceramic was fablicated by HIP base sintering method and contained a few at.% of LaF3 as a co-dopant to increase the transparency and mitigate divalent ytterbium ions (Yb
²⁺
) formation.