  Ultrahigh peak power femtosecond laser pulses create extreme states of matter
that are currently being probed with great interest. Plasma optics have been
proposed for shaping and amplifying high-power pulses, but they are subject to
huge modulations and fluctuations due to the very nature of excitation at high
intensities. Multidimensional characterization (spatial and temporal) of
relativistic plasma dynamics is therefore crucial to understand the
spatio-temporal structure of intense femtosecond pulses shaped by plasma
optics. This is, however, extremely difficult to achieve, particularly at the
low repetition rates typical at 100s terawatt to petawatt powers. Here, we
present a single-shot, three-dimensional (3D) spatio-temporal and
spatio-spectral measurement of such pulses based on spectral interferometry. We
reconstruct the 3D temporal structure of the laser pulse simultaneously
resolving the complex plasma dynamics. We demonstrate our method by measuring
the sub-picosecond evolution of relativistic solid-density plasmas. Our
measurements reveal that different spatial regions of the plasma surface move
differently yet exhibit a collective behavior globally. This all-optical
measurement technique captures 3D spatio-temporal effects within pulses with
ultrahigh peak powers, all in a single shot, enabling further progress in
ultrahigh-intensity laser and plasma technologies.
