Power scaling of a high-repetition-rate enhancement cavity

A passive optical resonator is used to enhance the power of a pulsed 78MHz repetition rate Yb laser providing 200fs pulses. We find limitations relating to the achievable time-averaged and peak power, which we distinguish by varying the duration of the input pulses. An intracavity average power of 18kW is generated with close to Fourier-limited pulses of 10W average power. Beyond this power level, intensity-related effects lead to resonator instabilities, which can be removed by chirping the seed laser pulses. By extending the pulse duration in this way to 2ps, we could obtain 72kW of intracavity circulating power with 50W of input power.