Carrier-Envelope Offset Frequency Stabilization in Solid-State Lasers: Direct Electro-Optic vs Pump-Power Modulation

The stabilization of the carrier-envelope offset frequency (f<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CEO</inf>) in mode-locked lasers has played a crucial role in trailblazing experiments awarded with two Nobel Prizes: first in 2005 [1] and more recently in 2023 [2]. The 2005 award honored the development of optical frequency comb technology, which necessitates locking of the f<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CEO</inf>, the more recent prize recognized the importance of absolute carrier-envelope phase (CEP) stabilization for generation of isolated attosecond pulses. In this paper, we compared two methods for achieving absolute CEP stabilization. The first approach is a standard pump modulation [3], whose bandwidth, however, is intrinsically limited by the fluorescence lifetime of the laser gain medium [4]. This limitation does not apply to a second technique relying on direct phase modulation implemented via an intracavity electro-optic modulator (EOM) [5]. Here, we experimentally investigate the performance of both approaches in a Cr:ZnS mode-locked laser. To the best of our knowledge, this is the first report of an EOM usage as an intracavity f<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CEO</inf> modulator in a solid-state laser.