Abstract
Localized surface plasmon polaritons (LSPPs) provide an efficient means of achieving extreme light concentration. In recent years, their active control has become a major aspiration of plasmonic research. Here, we demonstrate direct control of semiconductor bowtie antennas, enabling active excitation of LSPPs, at terahertz (THz) frequencies. We modify the LSPPs by ultrafast optical modulation of the free carrier density in the plasmonic structure itself, allowing for active control of the semiconductor antennas on picosecond timescales. Moreover, this control enables the manipulation of the field intensity enhancements in ranges of four orders of magnitude.
Highlights
Methods to guide and confine electromagnetic radiation in the smallest possible volume are generating new possibilities for imaging, spectroscopy and non-linear light-matter interactions beyond the diffraction limit [1]
Localized surface plasmon polaritons (LSPPs) provide an efficient means of achieving extreme light concentration. Their active control has become a major aspiration of plasmonic research
We modify the LSPPs by ultrafast optical modulation of the free carrier density in the plasmonic structure itself, allowing for active control of the semiconductor antennas on picosecond timescales
Summary
Methods to guide and confine electromagnetic radiation in the smallest possible volume are generating new possibilities for imaging, spectroscopy and non-linear light-matter interactions beyond the diffraction limit [1]. In order to overcome these limitations, in this article, we demonstrate that antennas made of semiconductor can support LSPPs resonances at THz frequencies These resonances can be actively controlled on ultrafast time scales by optical modulation of the free charge carriers in the semiconductor. This coupling is stronger for low values of the impedance, permittivity, of the conductor In this respect semiconductors are ideal candidates for active plasmonics in the THz regime: they provide an intrinsically better coupling of their free charges to electromagnetic fields due to their much lower permittivity compared to metals, but they provide the possibility of tuning this permittivity in a wide range by means of the free carrier concentration that can be controlled by material doping, through thermal, optical or electrical means. Several reports are available on the propagation of surface plasmon polaritons at semiconductor surfaces [2022], but LSPPs supported by individual semiconductor structures have not been demonstrated so far
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