Intrinsic spatial chirp of subcycle terahertz pulsed beams

We present an analysis of spatial chirp in subcycle pulsed beams corroborated by spatiotemporal electro-optic sampling measurements of terahertz radiation. Modeling the subcycle pulsed beam as a superposition of monochromatic Gaussian beams, free-space propagation is shown to directly lead to lateral spatial chirp with the spectrum on-axis substantially bluer than the overall energy spectrum. The two-transverse $+$ one-temporal dimensional profile of terahertz subcycle pulsed beams from organic crystals DSTMS and OH1 are measured and compared with observed spatiospectral correlations consistent with the model.