X-ray Pulses Approaching the Attosecond Frontier

摘要: Single soft-x-ray pulses of ∼90–electron volt (eV) photon energy are produced by high-order harmonic generation with 7-femtosecond (fs), 770-nanometer (1.6 eV) laser and characterized photoionizing krypton in the presence driver pulse. By detecting photoelectrons ejected perpendicularly to polarization, broadening photoelectron spectrum due absorption emission photons is suppressed, permitting observation a laser-induced downshift sub-laser-cycle resolution cross correlation measurement. We measure isolated x-ray 1.8 (+0.7/−1.2) fs duration, which shorter than oscillation cycle driving light (2.6 fs). Our techniques for measurement offer sub-femtosecond over wide range wavelengths, paving way experimental attosecond science. Tracing atomic processes evolving faster exciting field within reach.