Diffraction Interference Induced Superfocusing in Nonlinear Talbot Effect

We report a simple, novel subdiffraction method, i.e. diffraction interference induced superfocusing in second-harmonic (SH) Talbot effect, to achieve focusing size of less than λ_SH/4 (or λ_pump/8) without involving evanescent waves or subwavelength apertures. By tailoring point spread functions with Fresnel diffraction interference, we observe periodic SH subdiffracted spots over a hundred of micrometers away from the sample. Our demonstration is the first experimental realization of the Toraldo di Francia's proposal pioneered 62 years ago for superresolution imaging.