Radiation properties of high-order harmonic generation for the measurements of femto- and attosecond X-ray pulses

Radiation properties of high-order harmonic generation (HHG) are calculated for atoms in a strong laser field. The laser-duration dependence and the carrier-envelope-phase (CEP) dependence of HHG radiation properties are presented. The CEP dependence of the pure single distribution pulse of HHG radiation properties shows interesting 180° periodic structures. The quantum enhancement of the laser-assisted photo-ionization by femtosecond (1 fs=10⁻¹⁵ s) and attosecond (1 as=10⁻¹⁸ s) X-ray pulses and the interference patterns of photo-electron energy spectra are theoretically investigated. Transfer equations are presented for pulse reconstructions. The theoretical root-mean-square time (energy) differences of attosecond pulse reconstructions with different durations are less than 2 as (0.8 eV). These methods may be developed as basic techniques to access ultra-fast measurements and molecular movie. Supported by the National Natural Science Foundation of China (Grant No. 10675014)