Time Driven Subwavelength Focusing with Negative Refraction

Flat lens concept based on negative refraction proposed by Veselago in 1968 has been mostly investigated in monochromatic regime. It was recently recognized that time development of the super-lensing effect discovered in 2000 by Pendry is yet to be assessed and may spring surprises: Time-dependent illumination could improve the spatial resolution of the focusing. We investigate dynamics of flexural wave focusing by a 45\degre-tilted square lattice of circular holes drilled in a Duraluminium plate. Time-resolved experiments reveal that the focused image shrinks with time below diffraction limit, with a lateral resolution increasing from 0.8 $\lambda$ to 0.35 $\lambda$, whereas focusing under harmonic excitation remains diffraction limited. Modal analysis reveals the role in pulse reconstruction of radiating lens resonances, which repeatedly self-synchronize at the focal spot to shape a super-oscillating field.