Intensity improvement in the attosecond pulse generation with the coherent superposition initial state

► Simulating the HHG process irradiated from a model He+ ion in a two-color field. ► Preparing the initial active electronic state in the 1s and 2s superposition state. ► Finding the optimized chirp parameter of β=0.3 for the fundamental field. ► Observing the intensity enhancement in HHG with more than 6 orders of magnitude improvement. ► Generating a 34 as isolated attosecond pulse with similar intensity enhancement.