Generation of Subfemtosecond Deep and Vacuum UV pulses via Two-Photon Rabi Oscillations in Alkali Atoms or Alkaline Earth Ions

A method is proposed for the formation of femto- and subfemtosecond pulses of the deep ultraviolet and vacuum ultraviolet radiation via generating the third harmonic of femtosecond laser pulses during their resonant interaction with alkali atoms or alkaline earth ions. The pulse formation occurs due to two-photon Rabi oscillations between quasi-equidistant energy levels of atoms or ions. The duration of the generated third harmonic pulse is several times shorter than far from resonance, while the generation efficiency is up to 3-4 orders of magnitude higher.