Why not investigate wakes in plasmonics, such as Cherenkov waves, well-known from the acoustic bang that occurs when a jet-plane breaks the ultrasonic barrier? Patrice Genevet, Federico Capasso, et al. investigated such “supersonic” plasmon waves and present it in their talk at the CLEO 2015 conference. They excite the required plasmonic waves with specifically arranged small slit antennas in a metal film such as to design the phase of the plasmons that are excited and run along the metal surface. They generate waves whose phase velocity is higher than the waves supported by the unchanged standard interface. With resonator geometries and near-field scanning optical microscopy (NSOM) they then are able to observe Cherenkov waves, which they boldly call “super plasmonic waves”, in reminiscence of “super sonic waves”.
The key component of the experiments is indeed an experimental configuration that the authors around Federico Capasso recently introduced and published as a tool for versatile wavefront control: Arrays of short, small, deeply sub wavelength slits that are fabricated with FIB into a metal film. Depending on the angle of those effective antennas that varies along the antenna array it is possible to shape the phase of the running wave with high versatility, fundamentally as a superposition of many, tilted SPP sources. Searching for alternative applications, the group discovered the challenging idea of generating plasmonic Cherenkov waves.
The results were very well perceived by the audience. However, a critical comment highlighted that the system indeed has a quite important difference from acoustic Cherenkov waves. The waves emerge from the antenna array that is not moving in space. This is what makes Cherenkov waves in acoustics interesting. Hence, even as the effects are quite interesting as a playground application of a very interesting method, applications are not obvious. Anyway, it is a very nice demonstration of what is ultimately possible with free wave phase design in plasmonics.
- The short summary and full 2-page abstract (for full technical conference participators) at the CLEO 2015.
- List of recent publications on the Harvard website of the Capasso research group.
- N. Yu, and F. Capasso, "Flat optics with designer metasurfaces", Nature Materials, vol. 13, pp. 139-150, 2014. http://dx.doi.org/10.1038/nmat3839
- N. Yu, P. Genevet, M.A. Kats, F. Aieta, J. Tetienne, F. Capasso, and Z. Gaburro, "Light Propagation with Phase Discontinuities: Generalized Laws of Reflection and Refraction", Science, vol. 334, pp. 333-337, 2011. http://dx.doi.org/10.1126/science.1210713