100  mJ, 20  Hz Yb:YAG amplifier for seeding a high-energy OPCPA nanosecond pump laser

We present a 100 mJ Yb:YAG amplifier with a repetition rate of 20 Hz. The amplifier is built to seed a cryogenically cooled 10 J-class amplifier for pumping a high-energy optical parametric chirped pulse amplifier (OPCPA). Efficient OPCPA pumping requires a flat top pump pulse in space and time, so the pulses are shaped with an arbitrary waveform generator to ensure a flat profile at the output of the amplifier, even after any gain saturation effects. The amplifier presented here is built with simplicity and cost in mind and is specifically tailored to its purpose of seeding a high-energy, diode-pumped solid-state laser. The laser head is not cryogenically cooled, but it is operated at low temperatures (-7^∘C at full pumping) using optically bonded end caps on the laser crystal and a thermoelectric cooler. Excellent agreement between laser performance and numerical simulations is demonstrated.