Femtosecond frequency combs are among the most precise measurement tools in existence. They have applications ranging from high-precision spectroscopy and metrology to time-domain quantum physics. Maximizing the passive stability of these instruments is essential to achieve their full potential in fundamental science and high-tech industry. However, the noise mechanisms across the entire operating space of these devices have not been fully characterized. Here the noise properties of fiber-based frequency combs are studied as a function of intracavity dispersion, pump power, and repetition rate. Distinct minima are discovered in this parameter space where the free-running linewidth of the carrier-envelope offset (CEO) frequency f CEO drops below 1 kHz. The individual comb lines are analyzed spread over a wide spectral range producing a complete understanding of the particular contributions to the phase noise and their interplay. Exploiting these findings, combs featuring sharp teeth at specific frequency positions and over the entire spectrum from f CEO to 300 THz are demonstrated. The ultrabroadband stability offered by these compact systems provides a new level of quality for front-end measurement tasks in both time and frequency domains.

No abstract

Exploiting the interplay between cavity dispersion and pump power, we minimize the phase noise in mode-locked laser systems. Free-running femtosecond frequency combs with few-to sub-kHz linewidths over their entire ultrabroadband spectrum are demonstrated.