Quantum path control and isolated attosecond pulse generation with the combination of two circularly polarized laser pulses

Abstract

We theoretically investigate the quantum paths of the high-order harmonic generation (HHG) by using a left and a right circularly polarized Gaussian laser pulse with a proper time delay. When the carrier phase of the two pulses is ${\ensuremath{\varphi}}_{1}=0$, ${\ensuremath{\varphi}}_{2}=0.5\ensuremath{\pi}$, the ``gating'' structure of the combined laser field disappears. The numerical results indicate that no ``gating''-structure-combined laser pulse can control the quantum path. The HHG process is investigated by the semiclassical three-step model that makes use of a finite initial transverse velocity in the elliptically polarized field. For the case of ${\ensuremath{\lambda}}_{1}=800$ nm, ${\ensuremath{\lambda}}_{2}=1600$ nm, only a short quantum path contributes to the HHG, and an isolated attosecond pulse would be obtained. For the case of ${\ensuremath{\lambda}}_{2}=1600$, ${\ensuremath{\varphi}}_{2}=0.5\ensuremath{\pi}$, a supercontinuum spectrum plateau from 180 to 570 eV which includes the water window region is obtained, and attosecond pulses with the duration of about 75 as and a tunable central wavelength could be generated by superposing a bandwidth of 50 eV in the plateau area.