Abstract

One of the main goals of optics is the outdoing of the so-called diffraction limit. Stated simply, light spreads during propagation with an angle that is proportional to the ratio between the wavelength λ and the transverse size of the beam w₀, i.e., Δθ ∼ (w₀/λ)⁻¹. Distortion caused by a finite angular spread can be eliminated when Δθ ≪ 1, in so-called paraxial conditions. A method able to potentially avoid diffraction-induced-distortion across the entire range of possible values of w₀/λ, this including the high-resolution ∆θ ~ 1 conditions of so-called non-paraxial beams, is that of scale-free optical propagation, a phenomenon supported by the diffusive nonlinearity [1,2]. To date, this prediction has never been experimentally confirmed.We demonstrate experimentally scale-free propagation in photorefractive nanodisordered ferroelectric KTN:Li across the entire range of propagating optical waves, i.e., w₀/λ = 0.8–20 , see Fig. 1 ( λ =0.633 nm). We are able to observe non-diffracting geometric-optics-like propagation in one same material and experimental conditions, at once for quasi-plane-wave beams and for highly non-paraxial beams, with widths down to 0.5 µm (Fig. 1D, right) [3].

© 2015 IEEE