Superoscillations are band-limited functions with the counterintuitive property that they can vary arbitrarily faster than their fastest Fourier component, over arbitrarily long intervals. Modern studies originated in quantum theory, but there were anticipations in radar and optics. The mathematical understanding—still being explored—recognises that functions are extremely small where they superoscillate; this has implications for information theory. Applications to optical vortices, sub-wavelength microscopy and related areas of nanoscience are now moving from the theoretical and the demonstrative to the practical. This Roadmap surveys all these areas, providing background, current research, and anticipating future developments.

Band-limited functions can oscillate locally at an arbitrarily fast rate through an interference phenomenon known as superoscillations. Using an optical pulse with a superoscillatory envelope we experimentally break the temporal Fourier-transform focusing limit with a temporal feature that is approximately three times shorter than the duration of a transform-limited Gaussian pulse having a comparable bandwidth while maintaining 30% visibility. We experimentally demonstrate the ability of such signals to achieve temporal superresolution and show numerically in which cases such pulses can outperform transform-limited pulses.

We demonstrate both theoretically and experimentally the generation of a tunable two-dimensional superoscillating optical field through the interference of multiple Airy beams. The resulting pattern exhibits self-healing properties for a set of sub-Fourier diffraction spots with decreasing dimensions. Such spatial optical fields might find applications in microscopy, particle manipulation, and nonlinear optics.

The delivery of a super-oscillatory optical signal through a medium with an absorbing resonance at the super-oscillation frequency is considered theoretically and through simulations. While a regular signal oscillating at the absorption resonance frequency would be completely absorbed after a few absorption lengths, it is found that the superoscillation undergoes quasi-periodic revivals over optically thick distances. In particular revivals of extreme UV local oscillations propagating through Silica Glass over distances which are three orders of magnitude longer than the associated absorbing length are numerically demonstrated.

We show that it is possible to construct spectrally lower bound limited functions which can oscillate locally at an arbitrarily low frequency. Such sub-oscillatory functions are complementary to super-oscillatory functions which are band-limited yet can oscillate locally at an arbitrarily high frequency. We construct a spatially sub-oscillatory optical beam to experimentally demonstrate optical super defocusing.Comment: 14 pages, 4 figure