"New tools for precision metrology: Spatial Coherent Control and Ramsey Comb Spectroscopy."

"Direct frequency comb spectroscopy (DFCS) is a powerful application of frequency combs that is increasing in importance rapidly. In my talk I will discuss two new methods related to DFCS that we developed in our pursuit of precision spectroscopy of the ground states of helium and the helium-ion. The first method is spatial coherent control with comb laser pulses, which enables complex pattern formation and background elimination with two-photon DFCS. Secondly, I will discuss Ramsey-comb spectroscopy, which combines high pulse energies at the mJ level with the accuracy and resolution of frequency combs. It is based on a new laser system that can selectively and phase coherently amplify two frequency comb pulses at widely different time delays. The high pulse energy provides straightforward access to multi-photon transitions and nonlinear wavelength conversion, while the original frequency comb laser accuracy and resolution is fully recovered from a series of Ramsey-like measurements. The special properties of this approach, such as a cancelation of optical light-shift effects, are demonstrated by improving the accuracy of several weak two-photon transitions in atomic rubidium and cesium up to thirty times."