Repetition-rate-tunable femtosecond mode-locked Yb:GYSO laser in the sub-GHz regime

We report the successful implementation of a repetition-rate-tunable femtosecond mode-locked laser utilizing a Yb:GYSO crystal in the sub-GHz regime with tunability from 0.517 GHz to 0.881 GHz. Mode-locking was achieved using a semiconductor saturable absorber mirror (SESAM), and the total intracavity dispersion was set to negative values by incorporating a chirped concave mirror providing -1200 fs² group delay dispersion at 1045 nm, enabling stable operation in the soliton mode-locked regime. Detailed characterization at four distinct repetition-rate configurations showed that all mode-locked states maintained long-term stability for several hours without signs of instability. Input-output performances confirmed efficient laser operation with maximum output powers exceeding 400 mW and slope efficiencies above 25% across all configurations. In all cases, pulse durations remained below 200 fs near 1050 nm. These results clearly demonstrate that Yb:GYSO is a highly promising gain medium for efficient ultrafast laser operation in compact cavities requiring high-repetition-rate (GHz-level) operation.