Active f-to-2f Interferometer for Carrier-Envelope Phase Locking

Abstract

Carrier envelope phase (CEP) stabilization has proven an indispensable tool in attosecond science [1, 2] and precision frequency metrology [3]. Although fully CEP stabilized mode-locked fiber lasers and Ti:sapphire lasers are commercially available, CEP stabilization and all-optical frequency synthesis are still far away from general applicability to any given mode-locked laser. Stabilizability ultimately relies on the availability of at least 10 photons per pulse in the detection scheme [4]. Astro-combs, e.g., are rather demanding in this regard as they require ultra-high repetition rates. Moreover, despite their high pulse energies, thin-disk lasers have proven notoriously difficult to stabilize. Here we demonstrate that introduction of active optical gain into the infrared arm of an f-to-2f interferometer [5] can boost the signal by up to 20 dB, making stabilization of notoriously unstabilizable mode-locked lasers possible, e.g., high repetition-rate oscillators or thin-disk lasers.