Toroidal Lasing Spaser

Abstract

Toroidal shapes are often found in bio-molecules, viruses, proteins and fats, but only recently it was proved experimentally that toroidal structures can support exotic high-frequency electromagnetic excitations that are neither electric or magnetic multipoles. Such excitations, known as toroidal moments, could be playing an important role in enhancing inter-molecular interaction and energy transfer due to its higher electromagnetic energy confinement and weaker coupling to free space. Using a model toroidal metamaterial system, we show that coupling optical gain medium with high Q-factor toroidal resonance mode can enhance the single pass amplification to up to 65 dB. This offers an opportunity of creating the “toroidal” lasing spaser, a source of coherent optical radiation that is fueled by toroidal plasmonic oscillations in the nanostructure.

Electromagnetic toroidal excitations in matter and free space

“…3f). Finally, recent studies of toroidal excitations moved towards novel and active laser emitters 70 , and low-loss dielectric 71 (Fig. 3g) and superconducting 59 material systems.…”

“…Toroidal metamaterials provide useful platform for tailoring electromagnetic environment of complex symmetry and topology for light confinement, trapping and sensor applications (highly gradient electric filed is strong in the centre of the torus). Novel laser designs have been investigated where arrays of artificial toroidal "metamolecules" are uses as gain medium on the frequency of high-Q toroidal mode 70 . An emerging field of study is interaction of toroidal media with structured illumination: for instance toroidal "molecules" efficiently interact with vortex electromagnetic beams 85,86 .…”

Metamaterials at the University of Southampton and beyond

“…Toroidal resonances can destructively interfere with other modes of excitations in the materials, providing a new mechanism of induced transparency (slow light), and scattering suppression that can be used in narrow-band filters and for dispersion control. Novel laser designs have been investigated where resonant arrays of toroidal metamolecules are used as a gain medium [129]. Finally, toroidal electromagnetic excitations 5 Dependence of the absorption line width in a gas sample on the sample or beam size is a well-known effect.…”

All-optical Hall effect by the dynamic toroidal moment in a cavity-based metamaterial

“…As evidenced by the past decade, various optical phenomena have been demonstrated by metamaterials such as the negative refraction [23], super-imaging [24], plasmonically induced transparency [25], and cloaking [26]. From metamaterials with T r , interesting characteristics have been verified at microwaves as well as the infrared regime [12,[15][16][17][18][19][20][21][22]. However, these sophisticate toroidal structures have certain geometrical asymmetries, and thus are hard for nanofabrication.…”

“…Usually, they are readily masked by conventional multipole responses. Recently, dynamic T r realized in metamaterials [12,[15][16][17][18][19][20][21][22] may provide a platform to unveil the intriguing optics associated with it. As evidenced by the past decade, various optical phenomena have been demonstrated by metamaterials such as the negative refraction [23], super-imaging [24], plasmonically induced transparency [25], and cloaking [26].…”