Attosecond-pulse production using resonantly enhanced high-order harmonics

We study theoretically the effect of giant resonance in Xe on the phase difference between consecutive resonantly enhanced high-order harmonics and calculate the duration of the attosecond pulses produced by these harmonics. For certain conditions, resonantly induced dephasing compensates the phase difference which is intrinsic for off-resonance harmonics. We find these conditions analytically and compare them with numerical results. This harmonic synchronization allows attosecond-pulse shortening in conjunction with the resonance-induced intensity increase of more than an order of magnitude. The latter enhancement relaxes the requirements for the UV filtering needed for attosecond-pulse production. Using a two-color driving field allows a further increase of the intensity. In particular, a causticlike feature in the harmonic spectrum leads to a generation efficiency growth of up to two orders of magnitude, which is, however, accompanied by an elongation of the XUV pulse.

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