Effect of symmetric and asymmetric field ratios for polarization gating on high-order harmonic generation
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We simulate the high-order harmonic and attosecond pulse generation from the polarization gating pulse with equal and unequal ratios between the amplitudes of the two counter-rotation circular polarized pulses by using strong field approximation calculation and solving a 3D propagation equation. It is found that, when we keep the ionization probabilities at the end of the polarization gate the same, the effect of the field asymmetry is observed on the high-order harmonic cutoff in the frequency domain and the attosecond pulse duration in the time domain. When the harmonic chirp is compensated with help of a thin zirconium filter, our simulation demonstrates an isolated 61-as pulse can be generated from the polarization gating method with the asymmetric field ratio.