Abstract

The reduced peak power at gigahertz pulse repetition rates often requires additional external amplification for frequency metrology applications. Recently diode-pumped ytterbium solid-state lasers reached 6 GHz with 0.01-kW peak power [1] and 4.8 GHz with 0.9-kW peak power [2]. So far the onset of Q-switching instabilities has limited the peak power to <1 kW [3]. Here we present an all-optical limiter for Q-switching instabilities in a SESAM-modelocked laser oscillator to overcome this limitation. A Kerr-lens induces a diverging mode size on the SESAM which clamps the absorber fluence to a maximum and therefore limits the onset of Q-switched modelocking. We do not use Kerr lens modelocking because the gain mode size does not significantly vary over a large Kerr-lens focal range (Fig. 1a). With the Q-switching limiter we obtain stable cw modelocking with record-high peak power at a high repetition rate of 5 GHz. The Yb:CALGO laser delivers an average output power of 4.1 W with pulse durations as short as 96 fs which leads to a record-high peak power of 7.5 kW directly from the oscillator without pulse amplification or compression (Figs. 1d-f). This Q-switching limiter works well within the cavity stability regime and therefore does not require critical cavity alignments.

© 2015 IEEE