We demonstrate that the stability of the current optical frequency comb generated by a Kerr-lens mode-locked femtosecond laser is limited by the microwave reference used for phase locking the comb spacing. Hence we implement precision frequency/phase control of the entire comb to the fundamental and second-harmonic frequencies of a stable cw laser without any external microwave reference. The stability of a cw iodine-stabilized laser is transferred to millions of comb lines (with an instability of 3×10−13) covering more than one octave of the optical frequency spectrum. In addition, the mode spacing of the comb can be used as a stable microwave frequency derived directly from a stable optical oscillator.
Ye, Jun; Hall, John L.; and Diddams, Scott A., "Precision Phase Control of an Ultrawide-Bandwidth Femtosecond Laser: a Network of Ultrastable Frequency Marks across the Visible Spectrum" (2000). Physics Faculty Contributions. 83.