The development of optical metrology suited to ultrafast lasers has played a
key role in the progress of these light sources in the last few decades.
Measurement techniques providing the complete $E$-field of ultrashort laser
beams in both time and space are now being developed. Yet, they had so far not
been applied to the most powerful ultrashort lasers, which reach the PetaWatt
range by pushing the Chirped Pulse Amplification scheme to its present
technical limits. This situation left doubts on their actual performance, and
in particular on the peak intensity they can reach at focus. In this article we
present the first complete spatio-temporal characterization of a PetaWatt
femtosecond laser operating at full intensity, the BELLA laser, using two
recently-developed independent measurement techniques. Our results demonstrate
that, with adequate optimization, the CPA technique is still suitable at these
extreme scales, i.e., it is not inherently limited by spatio-temporal
couplings. We also show how these measurements provide unprecedented insight
into the physics and operation regime of such laser systems.