Time-resolved flatlens focusing beyond the diffraction limit

Flat lens concept proposed in 1968 by V.G. Veselago has been mostly investigated in the monochromatic regime. It was recently recognized that the time development of the superlensing effect is yet to be assessed and may spring surprises. Here we extend flat lens focusing to elastic waves in a thin plate. A 45°-tilted square lattice of circular holes drilled in a Duraluminium plate has been chosen to experimentally demonstrate focusing of flexural waves. Lamb wave pulse focusing is achieved below the first stop band. Time-resolved experiments reveal that the focused image shrinks with time below diffraction limit, with a lateral resolution increasing from 1.20 λ to 0.37 λ. Finite-difference time-domain simulations confirm the role in pulse reconstruction of  lens resonances which repeatedly self-organize in amplitude and phase to provide with super-oscillations.