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Flying Electromagnetic Toroids

Periodic Reporting for period 3 - FLEET (Flying Electromagnetic Toroids)

Reporting period: 2021-10-01 to 2023-03-31

Conventional transverse light waves propagate with the electric and magnetic field vectors aligned perpendicular to the propagation direction. Recent theoretical findings have shown that other waves exist with very different field structures. They also propagate at the speed of light, but only occur as short bursts of energy in the form of Flying Toroids (FTs). FTs possess a number of unique properties. Their broad bandwidth, and coupled spatial and temporal structure, shall allow for new schemes for telecommunications. They interact with matter in a unique way, promising new spectroscopy methods and light-enabled technologies. Such pulses can now be generated owing to advances in nanostructured materials and ultrafast lasers.

The objectives of the project are:

• To develop generators of FTs on the platform of nanostructured metasurfaces;
• To construct detectors with light-harvesting and light-rejecting nanostructures sensitive to FTs;
• To develop basic components for handling FTs, such as concentrators, deflectors, absorbers, splitters;
• To demonstrate free-space and waveguide communication lines with FTs;
• To establish novel forms of spectroscopy with FTs that provide new information for the analysis of material.
The results obtained during the report period can be summarized as follows:

1. For the first time we have developed and modelled a practical way of generating FTs. It is based on the conversion of short laser pulses into FTs using structured metasurfaces.

2. For the first time we have experimentally demonstrated generation of FTs in the optical part of the spectrum. We have developed metasurfaces that convert conventional pulses to Flying Toroids (FTs), leading to the demonstration of Flying Toroid (FTs) generation at near-infrared wavelengths. We have also developed a range of new ultrafast optical techniques that allow the full spatiotemporal characterization of electromagnetic fields of toroidal pulses.

3. For the first time, in collaboration Prof. T. Ellenbogen’ group, a leading THz group at Tel-Aviv University, we have experimentally demonstrated generation of FTs in the THz part of the spectrum. This approach depends on the conversion of short optical pulse into the envelope THz pulses on a dedicated metasurface.

4. We have introduced a new tomography methodology inspired from quantum mechanics, to quantify toroidal pulses with different spatiotemporal structures and this new methodology was used across all experiments for generation of FTs.

5. We have considerably extended understanding of the propagation dynamics of FTs pulses with account of their space-time non-separability. In particular, we have derived relations for the Fourier, Hankel and angular spectrum transforms of FTs, which describe the propagation of the FTs and will guide future work on controlling the corresponding dynamics.

6. As a very significant step in toroidal electrodynamics, we have discovered that FTs are a part of a broader family of Supertoroidal Pulses with field configurations analogous to topological excitations in solid state systems (skyrmions) with self-similar, fractal-like characteristics.

7. We have developed new spectroscopy for detecting toroidal and non-radiating (anapole) excitations in matter that is based on the monitoring the variations of optical properties of the sample with changes of dielectric environment (solvatochromism). We have demonstrated that our spectroscopy distinguishes toroidal and anapole modes from conventional excitations such as electric dipole modes.

8. We have studied computationally light-matter interactions with FTs and have shown that FTs can excite toroidal modes in dielectric particles while suppressing conventional modes.
The results reported in the previous section are novel, original and constitute significant advances in toroidal electrodynamics beyond the state-of-the-art.

Until the end of the project, we will focus on the propagation dynamics and light-matter interactions of FTs and their interaction with matter.

In particular:

1. We will experimentally study the propagation, focusing and diffraction of FT pulses and demonstrate information transfer schemes based on FTs.
2. We will advance the theory of supertoroidal pulses with focus on singularities, space-time non-separability and superoscillatory properties of FTs
3. We will develop practical detectors that can differentiate FTs from conventional electromagnetic radiation and detect them.
4. We will study the interaction of FTs with structured matter with a view of detecting for the first time space-time nonseparable electromagnetic excitations.
5. We will explore FTs-based spectroscopies to detect toroidal and anapole modes in structured matter.