Broadband Plasmon Nanofocusing: Comprehensive Study of Broadband Nanoscale Light Source

Abstract

Plasmonics, particularly the one based on plasmon resonances in optical antennas for the excitation of localized and enhanced light fields, have enabled numerous nanophotonics applications over the past few decades. One of the most common applications is to generate a nanoscale light source through plasmon resonance. An alternative phenomenon that has recently gained increasing attention for creating nanoscale light sources is plasmon nanofocusing, in which an enhanced nanoscale light field is generated at the apex of a tapered metallic structure through plasmons propagating on the tapered metallic structure toward the apex. As it is based on plasmon propagation, one of the interesting properties that the nanoscale light source carries is broadband, which cannot be achieved by optical antennas based on plasmon resonance. It is highly promising for optical techniques that require multiple wavelengths. Herein, for the full utilization of the broadband property for future applications, we present an extensive study regarding the broadband property of plasmon nanofocusing. Importantly, we reveal through numerical simulations that the broadband nanoscale light source spans over the entire visible to the near-infrared region. Moreover, we present the unique dependences of the broadband property on plasmonic materials and the geometry of tapered structures, which can be considered for different applications. These results are further confirmed by experimental demonstrations. Our comprehensive investigation focusing on the broadband property of plasmon nanofocusing provides fundamental and useful insights into various plasmonic techniques by introducing the high freedom of wavelengths at the nanoscale.