Super-sensing: 100-Fold enhancement in THz time-domain spectroscopy contrast via superoscillating waveform shaping

Superoscillations are a phenomenon where a band-limited wave may locally oscillate faster than its highest Fourier component. They are a product of destructive interference between the wave's constituent harmonics. In this article, we demonstrate that superoscillations enable a new functionality in linear optical sensing – the 100-fold enhancement in the optical contrast of the terahertz wave passing through two similar samples. To achieve this enhancement, we optimize the optical contrast in the time domain in a short observation window by varying the relative phases between the fundamental harmonics that make up the input terahertz wave. We find that the contrast is maximized when the wave intensity is minimized locally within the observation window, which naturally leads to the emergence of the superoscillations. We observe the 100-fold contrast enhancement both in our numerical simulations with Gaussian time-domain harmonics and in our experimental realization with narrow-band quasi-sinusoidal terahertz harmonics. Our results will have profound influence on terahertz sensing and imaging applications in medicine, pharmaceuticals, stand-off hazard detection, and nondestructive evaluation.