“…The MOPA system presented here is an upgraded secondgeneration version of our previous system [20], which produced 880 μJ at 2 kHz or 500 μJ at 10 kHz. Similar to [20], an ultrabroadband, few-cycle Ti:sapphire oscillator (Octavius-85M, MenloSystem, Inc.) is used as the front end and provides a seed at 1064 nm to optically synchronize the pump with the pulse to be amplified in the OPCPA. The seed is first amplified to 0.85 mW, 10 pJ at 85 MHz in a fiber amplifier, consisting of 5 m, single-mode, Yb-doped fiber (Nufern, Inc., PM-YSF-HI) pumped by up to 1 W optical power (AlfaLight, Inc., AM4-976A-10-253), a 3 nm bandpass filter centered at 1064 nm (No-vaWave Technologies, PMBP-06-N-B-Q), and optical isolators (OFR Thorlabs Inc., IO-L-T980/I1053-65), which is similar to [21].…”