Modern technology is heavily based on manipulations of radio frequency (RF) and optical radiation. Various technologies, for instance cell phones or optical communications, utilize electro-magnetic wave in high frequency regions with well-defined phase, causing innovations onto general society. Hence, it has been anticipated for decades attaining a low phase-noise oscillator in higher frequencies such as vacuum ultraviolet (VUV). However, since there are no conventional optical components usable for the VUV, we’ve never obtained any oscillator with a phase noise as small as that of phase-stabilized visible lasers. However, high harmonic generation (HHG) with passive intensity-enhancement cavities is now paving a road to Hz-level phase-coherent VUV. Since this HHG is based on passive optical cavities, the low phase noise of near-infrared pulses is possibly maintained to VUV pulses. On the other hand, this indicates that two major fields of pulse laser technology,

•  Frequency comb to precisely manipulate optical frequency and phase

•  HHG experiments toward short wavelength or short pulse width

are merging together.

In this project, low phase-noise VUV described above will be first developed, and UV high resolution spectroscopy will be preformed by exciting neutral atoms to their high energy states such as Rydberg states. Since this scheme coherently links highly excited states to the ground states, possibilities of future UV quantum manipulation will be searched. This scheme, as shown in the figure, explores a frontier of optical sciences by combining their subfields which have so far developed rather independently.