Abstract
Advanced nanophotonics penetrates into other areas of science and technology, ranging from applied physics to biology, which results in many fascinating cross-disciplinary applications. It has been recently demonstrated that suitably engineered light-matter interactions at the nanoscale can overcome the limitations of today’s terahertz (THz) photoconductive antennas, making them one step closer to many practical implications. Here, we push forward this concept by comprehensive numerical optimization and experimental investigation of a log-periodic THz photoconductive antenna coupled to a silver nanoantenna array. We shed light on the operation principles of the resulting hybrid THz antenna, providing an approach to boost its performance. By tailoring the size of silver nanoantennas and their arrangement, we obtain an enhancement of optical-to-THz conversion efficiency 2-fold larger compared with previously reported results for similar structures, and the strongest enhancement is around 1 THz, a frequency range barely achievable by other compact THz sources. We also propose a cost-effective fabrication procedure to realize such hybrid THz antennas with optimized plasmonic nanostructures via thermal dewetting process, which does not require any post processing and makes the proposed solution very attractive for applications.
Highlights
IntroductionNanoantennas have the form of an oblate spheroid with larger axis D and minor axis d, and these quantities are subject to optimization
We start our analysis with numerical calculations of a spheroidal silver (Ag) nanoantenna array arranged over a high-index gallium arsenide (GaAs) semiconductor substrate
The absorption enhancement has been calculated as the power absorbed in 100-nm GaAs surface film with silver nanoantenna array normalized to the power absorbed in the GaAs film without nanoantennas
Summary
Nanoantennas have the form of an oblate spheroid with larger axis D and minor axis d, and these quantities are subject to optimization It is well-known that such metallic ( Ag) nanoparticles provide localized plasmonic resonances in the optical range[34,35] that manifest themselves in a strong localization of the electric field near the nanoparticle due to conversion of the freely propagating incident waves into the near-field. The second absorption maximum is at the distances of 650–730 nm for the particles with radii ranging between 85 nm and 105 nm From these numerical calculations we may expect at least 4-fold enhancement of the THz photoconductive antenna performance with such optimized plasmonic nanostructures. The latter region of high absorption (650–730 nm distance between nanoantenna) is impractical for our case, since the sparse nanoantenna distribution cannot be achieved by laser dewetting that we use for the nanoantenna forming and tuning its size and distribution, at nanoantenna fabrication, we aim to the 280 nm spacing and radii of around 90 nm
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