Efficient Burst Mode Amplifier for Ultra-Short Pulses Based on Cryogenically Cooled Yb3+:CaF2

We present a novel approach for the amplification of high peak power femtosecond laser pulses at a high repetition rate. This approach is based on an all-diode pumped burst mode laser scheme. In this scheme, pulse bursts with a total duration between 1 and 2 ms can be generated and amplified, containing between 50 and 2000 individual pulses equally spaced in time. The individual pulses have an initial duration of 350 fs and are stretched to 50 ps in a chirped pulse amplification scheme. The first amplifier stage, which is described in detail in this work, is based on Yb3+:CaF2 cooled to 100 K. In this amplifier, a total output energy in excess of 600 mJ per burst at a repetition rate of 10 Hz is demonstrated. For lower repetition rates the total output energy per burst can be scaled to 915 mJ at longer pump duration. This corresponds to an efficiency as high as 25% from absorbed pump energy to extracted energy. This is – to our knowledge – the highest efficiency, which has so far been demonstrated for a pulsed Yb3+:CaF2 amplifier.