Generation of isolated attosecond pulses by polarization gating of high-order harmonic emission from H${}_2^{+}$ in intense ultrashort laser fields

Quantum-mechanical investigation is presented to study single attosecond pulse generation by gating high-order harmonic emission from H${}_2^{+}$ molecule in intense laser pulses with time-dependent ellipticity. The high-order harmonic generation from H${}_2^{+}$ molecule in superposition of a left and a right-hand circularly polarized Gaussian pulse is studied and the effect of time duration and carrier-envelope phase of laser field on single attosecond pulse generation is investigated. Using laser field formed by combination of a left and a right-hand elliptically polarized Gaussian pulse, the effect of ellipticity of field on duration and intensity of generated attosecond pulses is studied. The numerical calculations show that, with the conventional polarization gating, an intense single attosecond pulse can be isolated from the pulse train emitted by H${}_2^{+}$ molecule in the laser field.