Quantum path controlling in the presence of a low frequency field to generate isolated attosecond pulse

In this article, an efficient method is presented to generate an isolated attosecond pulse based on synthesized laser field. The 1D time-dependent Schrödinger equation is numerically solved for a helium atom exposed in a strong laser field. Two color fields containing a chirped laser pulse and its half harmonic as control pulse are modulated by a low frequency field to construct the configuration of strong laser field. The effect of low frequency field dominates the effect of the chirp parameter and extremely affects the acceleration step of high-order harmonic generation process. The low frequency field, in the optimized conditions, eliminates the long quantum path completely and only the short quantum path contributes in the higher harmonics emission mechanism. With such scheme, an extra supercontinuum with 700 eV bandwidth can be generated which supports the creation of a 64 attosecond isolated pulse. Moreover, the classical electron dynamics and the time–frequency analysis for explaining the underlying physics of atom–pulse interaction are also presented.