Ultrahigh-contrast petawatt laser with a mJ-class femtosecond parametric seeder for high-repetition-rate experiments

A novel, to the best of our knowledge, millijoule-class femtosecond optical parametric amplification-based source is implemented as a seeder in the high-repetition-rate HF-PW laser of ELI ALPS. High energy seeding results in a bandwidth corresponding to a sub-19 fs transform limit, significant gain reduction in the Ti:Sa amplifier chain, and an extremely low amplified spontaneous emission relative intensity of 2 × 10^-14 with 10 J compressed energy. The combination of the achieved parameters with the routinely available 2.5 or 5 Hz repetition rate offers unprecedented opportunities for the generation of particles and high harmonics.