Robustness of phase coherence against amplification in a flashlamp-pumped multi-pass femtosecond laser

We show that the phase of an ultra-short laser pulse undergoing the process of chirped-pulse amplification in a flashlamp-pumped multi-pass configuration is surprisingly well locked to the phase of the original pulse emitted by a mode-locked oscillator. We demonstrate that the relative phase jitter introduced in the amplification remains small (<0.1 rad r.m.s.) and does not spoil the visibility of fringes obtained in an interferometric experiment. These results indicate that, using a carrier-phase-stabilized seed laser, the generation of phase-controlled, high-intensity laser pulses is possible and relatively straightforward even with the commonly available flashlamp-pumped amplification systems.