Recent progress of attosecond XUV and X-ray pulses formed by high-harmonic generation

The laser pulses with several femtosecond duration close to its natural limit of the wave cycle in the visible spectral range are able to trace chemical processes of molecules. However, probing ultrafast transition process of electrons much faster than the wave cycle needs attosecond scale pulses. The experiments of attosecond XUV and X-ray pulses formed by high-harmonic generation have made much progress. The attosecond pulse train which are consecutive pulses with same carrier envelope phase can push optical frequency combs in the visible and near infrared wavelength to extreme ultraviolet regions. Temporal resolation of attosecond level is realized through measuring lateral distribution of the electron wave packet perturbed by laser ellipticity within attosecond temporal gate of electro