  Characterizing an isolated attosecond pulse (IAP) is essential for its
potential applications. A complete characterization of an IAP ultimately
requires the determination of its electric field in both time and space
domains. However, previous methods, like the widely-used RABBITT and attosecond
streaking, only measure the temporal profile of the attosecond pulse. Here we
demonstrate an all-optical method for the measurement of the space-time
properties of an IAP. By introducing a non-collinear perturbing pulse to the
driving field, the process of IAP generation is modified both spatially and
temporally, manifesting as a spatial and a frequency modulation in the harmonic
spectrum. By using a FROG-like retrieval method, the spatio-spectral phases of
the harmonic spectrum are faithfully extracted from the induced spatio-spectral
modulations, which allows a thoroughgoing characterization of the IAP in both
time and space. With this method, the spatio-temporal structures of the IAP
generated in a two-color driving field in both the near- and far-field are
fully reconstructed, from which a weak spatio-temporal coupling in the IAP
generation is revealed. Our approach overcomes the limitation in the temporal
measurement in conventional in situ scheme, providing a reliable and holistic
metrology for IAP characterization.
