Terahertz magnetic field enhancement in an asymmetric spiral metamaterial

Abstract

We use finite element simulations in both the frequency and the timedomain to study the terahertz resonance characteristics of a metamaterial (MM) comprising a spiral connected to a straight arm. The MM acts as a RLC circuit whose resonance frequency can be precisely tuned by varying the characteristic geometrical parameters of the spiral: inner and outer radius, width and number of turns. We provide a simple analytical model that uses these geometrical parameters as input to give accurate estimates of the resonance frequency. Finite element simulations show that linearly polarized terahertz radiation efficiently couples to the MM thanks to the straight arm, inducing a current in the spiral, which in turn induces a resonant magnetic field enhancement at the center of the spiral. We observe a large (approximately 20 times) and uniform (over an area of ∼ 10 µm 2 ) enhancement of the magnetic field for narrowband terahertz radiation with frequency matching the resonance frequency of the MM. When a broadband, single-cycle terahertz pulse propagates towards the metamaterial, the peak magnetic field of the resulting band-passed waveform still maintains a 6-fold enhancement compared to the peak impinging field. Using existing laser-based terahertz sources, our metamaterial design allows to generate magnetic fields of the order of 2 T over a time scale of several picoseconds, enabling the investigation of non-linear ultrafast spin dynamics in table-top experiments. Furthermore, our MM can be implemented to generate intense near-field narrowband, multi-cycle electromagnetic fields to study generic ultrafast resonant terahertz dynamics in condensed matter.

Photon diagnostics at the FLASH THz beamline

“…It will be permanently installed inside the THz beamline vacuum environment for distortionfree THz spectrum measurements, enabling quick and robust spectral studies [e.g. suitable for THz shaping by emerging THz meta-materials (Yen et al, 2004;Monticone & Alù , 2017;Stojanović et al, 2018;Polley et al, 2018)].…”

Active photonic platforms for the mid-infrared to the THz regime using spintronic structures

“…Besides, it has been shown that the MO activity of magnetoplasmonic structures can be enhanced by putting the MO active material at particular places within the structure [121,122]. On the other hand, metamaterials structures have shown their ability to design tailored electromagnetic fields in a very wide spectral range [123], and resonant meta-atoms with both plasmonic and (opto)-magnetic functionalities have shown great potential [124]. Therefore, exploring the use of metamaterials to maximize the electromagnetic field at the position of the spintronic component may be a way to further improve the performance of MRE based photonic platforms.…”

Coupling phenomena and collective effects in resonant meta-atoms supporting both plasmonic and (opto-)magnetic functionalities: an overview on properties and applications [Invited]

“…Novel possibilities of optical control of magnetism on the nanometer scale via plasmonic resonances have emerged as well it was shown that femtosecond laser pulses [ 212 ] are able to generate magnons with nanometer wavelengths [213]. Moreover, intriguing new magnetic phenomena can be triggered in the THz region of the light spectrum [ 214 ], and fundamental efforts have been recently emerged in this direction to design metamaterials working in that frequency region to manipulate locally magnetic properties of matter [215,216]. Indeed, one of the missing pieces of this intricated puzzle is a systematic exploration of the fundamental properties of magneto-plasmonic metamaterials between the visible/near-infrared and the THz regions.…”