  Controlling the carrier envelope phase (CEP) in mode-locked lasers over
practically long timescales is crucial for real-world applications in ultrafast
optics and precision metrology. We present a hybrid solution that combines a
feed-forward technique to stabilize the phase offset in fast timescales and a
feedback technique that addresses slowly varying sources of interference and
locking bandwidth limitations associated with gain media with long upper-state
lifetimes. We experimentally realize the hybrid stabilization system in an
Er:Yb:glass mode-locked laser and demonstrate 75 hours of stabilization with
integrated phase noise of 14 mrad (1 Hz to 3 MHz), corresponding to around 11
as of carrier to envelope jitter. Additionally, we examine the impact of
environmental factors, such as humidity and pressure, on the long-term
stability and performance of the system.
