Carrier-envelope phase stabilization of femtosecond lasers by the direct locking method

The progress of carrier envelope phase (CEP) stabilization by the direct locking method developed at KAIST is summarized. The CEP of a femtosecond laser pulse has become a new laser parameter when the electric field of laser pulses, instead of the intensity, becomes a crucial interacting variable. The basic principle of the direct locking method is first explained, which operates in the time domain and generates CEP-stabilized laser pulses with identical CEP from a femtosecond oscillator. Then the method to achieve a long-term CEP stabilization, realized by installing a double feedback loop to a femtosecond laser, is explained. In addition the frequency-domain characteristics of the CEP-stabilized femtosecond laser are also analyzed. Finally the CEP stabilization of a kHz high-power femtosecond laser is presented.