Abstract

Most of the tunable Yb-doped fiber lasers exploit the quasi-four-level system between 1030-1100 nm [1-2]. Extending the tunability over the whole emission bandwidth of Yb-glass and therefore covering the wavelengths between 976 nm and 1020 nm requires (i) reaching transparency and (ii) controlling the gain competition between short wavelengths (three-level transition) and 1030 nm emission (quasi three-level transition) [3-4]. For higher wavelengths above 1070 nm, the reabsorption and the emission are weak. The laser scheme is in this case, a nearly pure four-level system where the gain is proportional to the overall upper-state population [5].

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