Single attosecond pulse generation
Attosecond pulses are produced by high-harmonic generation from a driving laser
pulse at high intensity.
Isolated single attosecond laser pulses can be generated from a few-cycle
fundamental pulse by selection of high-energy cutoff harmonics or by
using the polarization gating technique. The latter method makes use of the
strong dependence of the harmonic signal on the ellipticity of the driving
pulse. The ellipticity dependence intensifies when the wavelength of the
generating field increases, numerical results however indicate that it
saturates in the mid-infrared. Isolation of single attosecond pulses by the
polarization gating techique is therefore found to be more efficient at
these long wavelengths as compared to the Ti:sapphire wavelengths. Consequently,
longer driving pulses with more cycles can be used in the mid-infrared compared
with the near-infrared to obtain a single attosecond pulse.
This can be readily seen from the displayed time-frequency analysis.
F. He et al., Opt. Lett. 32 (2007) 3224