Direct electro-optic phase control for carrier-envelope offset frequency stabilization in solid-state lasers

Carrier-envelope offset frequency (f_ceo) stabilization in mode-locked lasers is typically implemented by active pump power control. Yet, the bandwidth of this technique is intrinsically limited by the finite response time of the gain medium to pump power changes. In this paper, we present a novel approach for f_ceo stabilization in solid-state laser oscillators, which leverages the linear electro-optic effect to directly control the evolution of the carrier-envelope phase. We validate this concept by implementing a lithium niobate electro-optic modulator (EOM) in a Kerr-lens mode-locked Cr:ZnS laser. Our experiments prove that without the gain-medium-related limitation EOM-based f_ceo stabilization provides superior performance (6.6 mrad phase noise integrated in the frequency range of 10 Hz - 12.5 MHz) over the standard pump-modulation method (7.6 mrad). Nevertheless, we identify another bandwidth constraint arising from the piezoelectric effect in lithium niobate crystal, which causes an acoustic resonance at a frequency dependent on the EOM size. We study the response of the EOM f_ceo actuators depending on their dimensions and provide guidelines for further improvement of f_ceo stability in solid-state lasers.