Abstract

In recent years, Yb³⁺ 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 Yb³⁺-doped CaF₂ ceramic based material, Yb³⁺-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 (Yb²⁺) formation.

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