The versatile manipulation of electron motion on the atomic scale calls
for the shaping of the electric field evolution of light within a
single cycle. The super-octave bandwidth required for this task
dramatically increases the probability of formation of spatio-temporal
distortions. As a result, the accuracy of physical observables can be
extremely compromised by spatial averaging unless the complete
spatio-temporal field information is known. Here, we apply spatially
resolved electro-optic sampling to record three-dimensional
electric-field structure of a sub-cycle synthesized light transient
carrying wavelengths from 700 to 2700 nm. We show an in-depth
picture of the field synthesis process, disclosing how temporal,
spectral, and global-phase properties of the synthesized pulse vary
across space, including the propagation direction around the focal
point where the transient is generated.