High-accuracy deep-UV Ramsey-comb spectroscopy in krypton

In this paper, we present a detailed account of the first precision Ramsey-comb spectroscopy in the deep UV. We excite krypton in an atomic beam using pairs of frequency-comb laser pulses that have been amplified to the millijoule level and upconverted through frequency doubling in BBO crystals. The resulting phase-coherent deep-UV pulses at 212.55 nm are used in the Ramsey-comb method to excite the two-photon 4p(6) -> 4p(5) 5p[1/2](0) transition. For the Kr-84 isotope, we find a transition frequency of 2829833101679(103) kHz. The fractional accuracy of 3.7x 10(-11) is 34 times better than previous measurements, and also the isotope shifts are measured with improved accuracy. This demonstration shows the potential of Ramsey-comb excitation for precision spectroscopy at short wavelengths.