A numerical simulation of attosecond harmonic pulse generation in a three-dimensional field-ionizing gas is presented. Calculated harmonic efficiencies quantitatively reproduce experimental findings. This allows a quantitative characterization of attosecond pulse generation revealing information currently not accessible by experiment. The rapid phase variation and spatiotemporal distortions of harmonics are smaller than anticipated, allowing focusing of 30-nm, 750-as pulses to intensities in excess of ${10}^{13}\mathrm{W}/{\mathrm{cm}}^2$. Feasibility of such pulses brings novel applications such as extreme ultraviolet nonlinear optics and attosecond pump probe spectroscopy within reach.

• Received 28 March 2001

DOI:https://doi.org/10.1103/PhysRevLett.88.093905