Attosecond pulse generation isolated with a polarization-ionization gating scheme

We theoretically simulate high harmonic generation in the frequency domain and attosecond pulse generation in the time domain from helium atom irradiated by a combined field, which is synthesized by a 4 fs, 800 nm x-polarized pulse and a 4 fs, 800 nm y-polarized pulse with a certain time delay. Different from harmonic spectrum generated by the x-polarized pulse alone, the harmonic spectrum from the combined field shows two supercontinuum regions, one supercontinuum spectrum with slight modulation ranges from the 35th to 90th order, and another supercontinuum spectrum ranges from the 185th to 285th order. This phenomenon is attributed to the dual gating of the harmonic emission by the polarization and the ionization in the case of combined pulses. After inverse Fourier transform, an isolated 108 as pulse can be obtained by superposing supercontinuum harmonics from the 185th to the 285th order