Geometric scaling of laser-driven proton focusing from hemispherical foils

We systematically characterize the focusing behavior of laser-driven proton beams from hemispherical targets of various diameters using mesh radiography. The proton focal location is inferred to be near the geometrical center for the smallest tested hemisphere ( Ψ = D hemi / D Laser = 6.1 ). However, larger hemispheres ( Ψ = 14.6 ) degrade the focusing behavior and behave more like flat foils with focal location significantly inside the hemisphere. We also infer a tight virtual focus of 9 ± 3 μ m through a mesh transition analysis.