  The physics of high harmonics has led to the generation of attosecond pulses
and to trains of attosecond pulses. Measurements that confirm the pulse
duration are all performed in the far field. All pulse duration measurements
tacitly assume that both the beam's wavefront and intensity profile are
independent of frequency. However, if one or both are frequency dependent, then
the retrieved pulse duration depends on the location where the measurement is
made. We measure that each harmonic is very close to a Gaussian, but we also
find that both the intensity profile and the beam wavefront depend
significantly on the harmonic order.
  Thus, our findings mean that the pulse duration will depend on where the
pulse is observed. Measurement of spectrally resolved wavefronts along with
temporal characterization at one single point in the beam would enable complete
space-time reconstruction of attosecond pulses. Future attosecond science
experiments need not be restricted to spatially averaged observables.
