The authors present a method to stabilize the carrier-envelope phase of femtosecond mode-locked lasers using frequency-domain stabilization techniques. This stabilization allows for precise control of the absolute optical frequencies emitted by the laser, which can be directly referenced to a stable microwave clock. The technique involves comparing the frequency of comb lines on the low-frequency side of the optical spectrum with those on the high-frequency side, which have approximately twice the frequency. By stabilizing both the pulse repetition rate and the offset frequency, the relative carrier-envelope phase can be controlled. The self-referencing technique does not require external optical input and can be used to perform absolute optical frequency measurements with a single mode-locked laser. This approach has significant implications for extreme nonlinear optics and optical frequency metrology, making it a powerful tool for precise frequency measurements.The authors present a method to stabilize the carrier-envelope phase of femtosecond mode-locked lasers using frequency-domain stabilization techniques. This stabilization allows for precise control of the absolute optical frequencies emitted by the laser, which can be directly referenced to a stable microwave clock. The technique involves comparing the frequency of comb lines on the low-frequency side of the optical spectrum with those on the high-frequency side, which have approximately twice the frequency. By stabilizing both the pulse repetition rate and the offset frequency, the relative carrier-envelope phase can be controlled. The self-referencing technique does not require external optical input and can be used to perform absolute optical frequency measurements with a single mode-locked laser. This approach has significant implications for extreme nonlinear optics and optical frequency metrology, making it a powerful tool for precise frequency measurements.