Optical frequency measurement across a 104-THz gap with a femtosecond laser frequency comb

Abstract

The frequency-domain mode comb of a Ti:sapphire femtosecond laser centered at 350 THz is broadened to 150 THz (full width at $-30 \mathrm{dBc}$) by self-phase modulation in a single-mode optical fiber. By phase locking continuous-wave lasers to elements of the comb near 1064 and 778 nm, we measure the 104-THz frequency gap between these two lasers with a relative uncertainty of $2.7\times {10}^{-11}$ in 1 s.