Abstract
The THz response of slit structures and split-ring resonators (SRRs) featuring extremely small gaps on the micro- or nanoscale is investigated numerically. Both structures exhibit strong field enhancement in the gap region due to light-induced current flows and capacitive charging across the gap. Whereas nanoslits allow for broadband enhancement the resonant behavior of the SRRs leads to narrowband amplification and results in significantly higher field enhancement factors reaching several 10,000. This property is particularly beneficial for the realization of nonlinear THz experiments which is exemplarily demonstrated by a second harmonic generation process in a nonlinear substrate material. Positioning nanostructures on top of the substrate is found to result in a significant increase of the generation efficiency for the frequency doubled component.
Highlights
The last decades have seen significant progress in the development of terahertz (THz) technologies in a wide variety of fields such as chemical recognition, material inspection, or security control
We have analyzed the response of slit structures as well as THz split-ring resonators featuring extremely small gaps on the micro- or nanoscale
Application of the structures was exemplarily demonstrated by a second harmonic generation process in a nonlinear substrate material
Summary
The last decades have seen significant progress in the development of terahertz (THz) technologies in a wide variety of fields such as chemical recognition, material inspection, or security control. One of the major and yet unmet limitations is that, compared to the optical regime, the pulse energies supplied by current THz sources are still rather limited. This is problematic for the realization of nonlinear THz experiments which have been a topic of considerable interest in recent years. The highest average THz power is currently available from large-scale electron particle accelerators [1]. Using table-top sources generation of high energy THz pulses has been demonstrated using for example large area photoconductive switches [2], frequency mixing in a laser generated plasma [3], or optical rectification in nonlinear crystals [4].
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