Efficient polarization gating of high-order harmonic generation by polarization-shaped ultrashort pulses

Polarization gating of high-order harmonic generation takes advantage of the significant reduction of harmonic generation efficiency for elliptically polarized excitation fields, in order to generate short bursts of harmonic radiation from relatively long pulses. We show that the currently used method for generation of polarization gated pulses using wave-plate combinations is inefficient, and propose an alternative method based on polarization pulse shaping techniques. This method is shown to be significantly more efficient and to enable significant shortening of the gate duration. Using this scheme, isolated attosecond pulses should be achievable with excitation pulses of a duration as long as 20 fs.