Superspectroscopy: 100-Fold enhancement in THz time-domain spectroscopy contrast via superoscillating waveform shaping*

In modern physics, spectroscopy is one of the most powerful tools that one can use to study structures of materials. One common application of spectroscopy is to distinguish similar materials. In our recent work, we have experimentally demonstrated that for a band-limited time-domain spectroscopic system, its capability to distinguish similar materials can be enhanced by introducing time-domain superoscillation. With the same 'discriminability' concept we used in our recent work to quantify the 'capability to distinguish', we will show that out of the many possible waveforms that could exist in a band-limited time-domain spectroscopy system, superoscillation is the waveform that produces the best discriminability. We will demonstrate this idea with a simplified analytical model, a more realistic numerical simulation, and an time-domain THz spectroscopy experiment. We also point out that, when compared with its Fourier components, superoscillation has about the same level of advantage in discriminability no matter how similar the materials are. We experimentally demonstrate that superoscillation achieves a two-order-of-magnitude improvement in discriminability between optically similar materials. The immediate implication of this work is that the same level of contrast enhancement can be achieved by superoscillating waveform shaping in THz time-domain imaging.