Femtosecond lasers in precision time and frequency metrology

Summary form only given. As a recent test of the femtosecond-laser-based optical clockwork, we have compared two femtosecond lasers that have their spectra broadened to /spl sim/300 THz in microstructure fiber. The discrete frequency modes of each octave-spanning spectrum are phase-locked to a common continuous wave laser. The measured instability of the heterodyne beat between the two femtosecond systems demonstrates that the intrinsic noise of each system is /spl les/6.3 /spl times/ 10/sup -16/ in 1 s of averaging across the 300 THz bandwidth. Furthermore, the average frequencies of the frequency modes of the two systems are found to agree within an uncertainty of /spl les/4 /spl times/ 10/sup -17/ across the entire octave. This demonstrates the possibility to transfer the sub-Hertz stability and accuracy of the best current optical standards to /spl sim/500,000 individual oscillators across the visible and near-infrared spectrum.