Generation of isolated attosecond pulses from atoms driven by optimized two near-infrared pulses and their second harmonic fields

With the rapid development of laser technology, it is possible to control optical waveforms by coherent superposition of electric fields with multiple color components, which creates conditions for generating the ultrashort isolated attosecond pulses (IAP). Based on the strong-field approximation theory, this work focuses on the IAP generated by the optimized multicolor field synthesized by two fundamental near-infrared lasers and their second harmonic fields. The results show that by applying frequency-doubled pulses to the near-infrared laser fields and optimizing the laser parameters, the emission properties of high order harmonics from single atom can be greatly improved, and the nearly attochirp-free harmonic emission can be realized within a certain energy range. As a result, shorter IAPs are obtained. With the consideration of the macroscopic propagation effect of gas, the IAP with a pulse width up to 40 as is generated under appropriate experimental conditions. Finally, the effects of gas pressure on the properties of the high-order harmonic and attosecond pulses are also investigated. This study provides useful theoretical guidance for generating ultra-short IAPs with near-infrared laser pulses in experiment.