Generation Of Isolated Attosecond Pulsesby Optimizing Parameters Of Two-color Field

High-order harmonic generation (HHG) can be emitted from atoms and moleculesdriven by the interaction of intense laser field. Attosecond pulse chain is generatedthrough superposing pulses having different energy in flat region of HHG. But anisolated attosecond pulse is hoped to generate due to its realistic appliance.1. Based on the classical theory, in this paper we optimize the intensity ratio ofbasic frequency field and low frequency field in the combined field. Then solvingtime-dependent Schrodinger equation of one-dimensional model helium atom drivenby the optimized combined field, we find that high-order harmonic generation cut-offposition of helium atom is extended. In addition, taking into account the initial phaseof the basic frequency field, we obtain an isolated sub-37attosecond pulse from thehigh-order harmonic generation of Helium atom driven by the combined field.2. We propose that helium atom is driven by a multi-cycle combination laser pulseof an infrared pulse and a polarization gating. It is propitious to generate an isolatedattosecond pulse that effective cycle numbers of the linearly polarized pulse can bechosen with controlling the width of gating. It is propitious to enhancing cutoff ofHHG that the returning electron possesses a strong kinetic energy because of infraredpulse. We use strong field approximation theory to investigate the HHG spectrum andobtain a narrow isolated attosecond pulse.3. We study solving numerically time-dependent Schr dinger equation by splittingof operators, regards the harmonic oscillator as research object, solve numericallytime-dependent Schr dinger equation of one-dimensional harmonic oscillator bysecond-order and third-order accurate splitting of operators, respectively. We comparethe truncation errors (number value and exact solutions) in the two schemes. It isshown that the numerical wave function investigated by the high order accuratesplitting of operator is better than by the low order. It is useful to obtain highprecision wave function from solving numerically time-dependent Schr dingerequation.