Generating Isolated Elliptically Polarized Attosecond Pulses Using Bichromatic Counterrotating Circularly Polarized Laser Fields

We theoretically demonstrate the possibility to generate both trains and isolated attosecond pulses with high ellipticity in a practical experimental setup. The scheme uses circularly polarized, counterrotating two-color driving pulses carried at the fundamental and its second harmonic. Using a model Ne atom, we numerically show that highly elliptic attosecond pulses are generated already at the single-atom level. Isolated pulses are produced by using few-cycle drivers with controlled time delay between them.

Figure 1

Spectra for (a) $1s$, (b) $2p_{+}$, (c) $2p_{-}$ initial states, and (d) equal mixture of $2p_{+}$ and $2p_{-}$ states. Colors mark harmonics corotating (red) and counterrotating (blue) with the $\omega$ field.

Figure 2

Time-resolved XUV emission intensity and ellipticity from (a),(b) $1s$ and (c),(d) $2p$ orbitals. Color in (b) and (d) indicates the ellipticity of the spectral components in the regions where the amplitude of the spectrogram is significant. The horizontal dashed lines mark the $I_p$.

Figure 3

Time-resolved XUV emission from a $2p$ orbital, for time-delayed 4 fs full width at half maximum 800 and 400 nm pulses. (a) Spectral intensity and (b) time-dependent ellipticity for perfect overlap of the two pulses. (c) Spectral intensity and (d) time-dependent ellipticity for the two-pulse delay of 2.6 fs. Spectra in (c) is multiplied by a factor of 2 to enhance the contrast. Color in (b) and (d) indicates the ellipticity of the spectral components in the regions where the amplitude of the spectrogram is significant. The horizontal dashed lines mark the $I_p$.