Ultrafast radially-polarized laser beams having spatio-temporal couplings and broken symmetry

Radially-polarized laser-beams (RPLBs) are a low order vector beam having a non-zero longitudinal electric field E z at the on-axis ( r = 0) position, which becomes significant when tightly focused. The large longitudinal field in ultrashort RPLBs has long been a motivation for acceleration of electrons to high energies in free space [1] , [2] along with other field-sensitive strong-field interactions. Because such interaction are so sensitive to the precise field and propagation characteristics of the driving laser, it is important to consider imperfections or exotic shaping to understand potential effects, and if there is a path towards optimization or control. We develop a model to consider the effect of spatio-temporal couplings (STCs) on the field of ultrashort RPLBs when tightly focused [3] ( Fig. 1a ). STCs are generally aberrations that lead to the description of the electric field being inseparable between space and time, and are analogous to chromatic aberrations.