Vacuum ultraviolet frequency comb spectroscopy with phase controlled ultrafast laser pulses.
Since a few years infrared frequency comb lasers have made it possible to measure optical frequencies of hundreds of THz directly in comparison with an atomic clock. This development has revolutionized optical precision spectroscopy, atomic clocks and ultrafast laser science. At the LCVU we are working on methods to extend the frequency comb principle to much shorter wavelengths such as vacuum ultraviolet (VUV) and extreme ultraviolet for precision spectroscopy of helium and hydrogen-like ions. A recent experiment will be discussed were we demonstrate frequency comb spectroscopy in Xe atoms at 125 nm, using VUV pulses obtained by phase-stable amplification and harmonic generation of multiple pulses from a frequency comb laser. It is shown that frequency combs can be used in this way to obtain a resolution better than a MHz in the vacuum ultraviolet and shorter wavelengths, although the excitation pulses derived from the comb laser have a bandwidth on the order of a THz.