Space-time characterization of ultra-intense femtosecond laser beams

Femtosecond lasers can now deliver ultrahigh intensities at focus, making it possible to induce relativistic motion of charged particles with light and opening the way to new generations of compact particle accelerators and X-ray sources. With diameters of up to tens of centimetres, ultra-intense laser beams tend to suffer from spatiotemporal distortions, that is, a spatial dependence of their temporal properties that can dramatically reduce their peak intensities. At present, however, these intense electromagnetic fields are characterized and optimized in space and time separately. Here, we present the first complete spatiotemporal experimental reconstruction of the field E(t,r) for a 100 TW peak-power laser, and reveal the spatiotemporal distortions that can affect such beams. This new measurement capability opens the way to in-depth characterization and optimization of ultra-intense lasers and ultimately to the advanced control of relativistic motion of matter with femtosecond laser beams structured in space-time.