High precision measurement and generation of optical and microwave frequencies using narrowband and short-pulse lasers

Abstract

Since the advent of the laser, more than forty years ago, the development of narrow-band single-frequency and high-spectral-purity sources has been quite separated from the efforts in the generation of short pulse, high-bandwidth mode-locked lasers. Today we have continuous-wave, single-frequency lasers with linewidths smaller than one Hertz, along with mode-locked lasers emitting pulses of only a few femtoseconds and whose spectra can cover an entire octave. These two classes of lasers have met recently in the field of metrology and nonlinear optics. It has been realized that the active control techniques traditionally used to reduce FM noise in single-frequency lasers, thus reducing their linewidths, could be used to stabilize the frequency comb which constitutes a mode-locked laser. By stabilization of both the repetition rate and the carrier-to-envelope offset of a femtosecond laser, a direct phase-coherent link between microwave and optical frequencies is possible, allowing for example the direct measurement of optical frequencies. A dramatic development from this has been the advent of optical atomic clocks. With stabilities and accuracies an order of magnitude higher than the conventional microwave clocks, they are opening a new era in precision measurements and will have great impact, for example, in navigation and telecommunications. Another close potential application is the development of optical frequency synthesizers, which can generate high-spectral-purity optical and microwave frequencies in a phase-coherent way. In this talk, an overview of these developments is given, along with the present status of our work towards frequency measurement and synthesis and the development of an optical atomic clock based on cold calcium atoms.