Long-term stable passive synchronization of 50 µJ femtosecond Yb-doped fiber chirped-pulse amplifier with a mode-locked Ti:sapphire laser.

We report long-term stable passive synchronization of a femtosecond Yb-doped fiber chirped-pulse amplifier (CPA) with a mode-locked Ti:sapphire laser for pump-seed synchronization of an optical parametric chirped-pulse amplification (OPCPA) system. The fiber CPA system delivers pulses with a wavelength of 1035 nm, energy of 50 µJ, and duration of 690 fs at a repetition rate of 0.4 MHz. The seed fiber oscillator is passively synchronized with a mode-locked Ti:sapphire laser by injection of the Ti:sapphire laser pulses into the cavity of the fiber oscillator. The second harmonic (SH) output with a wavelength of 518 nm, energy of 18 µJ, and duration of 1.2 ps was prepared for the OPCPA pump. The measured timing jitter between the pump (fiber SH) and the seed (Ti:sapphire) was 42 ± 14 fs, while the jitter between two oscillator outputs was 1.4 ± 0.5 fs. The robust synchronization technique allows long-term stable operation over 8 h.