Terahertz non-linear optics in 2D materials and van der Waals topological metamaterials

Date

Dec 4, 2025

Time

1:00 PM - 3:00 PM

Speaker

Miriam S. Vitiello

Affiliation

NEST, CNR-NANO and Scuola Normale Superiore, Pisa (Italy)

Series

TUD nanoSeminar

Language

en

Main Topic

Materialien

Other Topics

Materialien

Host

Arezoo Dianat

Description

Optical nonlinearity in the terahertz (THz) range represents a key technology to access high frequency spectral windows that are usually difficult to cover using conventional solid state laser technologies. Over the past decade, the non-linear optical properties of graphene have been extensively investigated, and a wide range of related applications demonstrated, ranging from optical modulators [1] to saturable absorbers [2]. High harmonic generation (HHG) – the frequency up-conversion of an optical signal – in materials systems is governed by symmetries. This effect has been exploited in graphene [3], where HHG has been demonstrated, albeit only at odd multiples of the driving frequency owing to its inherent centro-symmetry. In topological insulators (TIs), unconventional HHG has been predicted [4], supported by the bulk and topological surface states, which are usually difficult to distinguish, relying on the ultrafast intraband dynamics, and the inversion symmetry- breaking even order nonlinearity in the topological phase. Here, we exploit innovative technological approaches in large area topological insulator metametarials and heterostructures or multilayer graphene to device both high efficient non-linear micro-devices, optically pumped by quantum cascade lasers (QCLs) delivering 2W optical power, and electrically driven integrated plasmonic lasers comprising integrated QCL heterostructures, targeting HHG in the technologically relevant Reststrahlen gap (6-12 THz) at both odd or even orders, via symmetry breaking [5], [6], [7]. This talk will provide future perspectives in the fascinating field of topological photonics and non-linear THz photonics.
 <section class="references">
 <div class="ref-title">References</div>
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 <span style="width: 2.5em; flex-shrink: 0;">[1]</span>
 <span>A. Di Gaspare et al., Electrically Tunable Nonlinearity at 3.2 Terahertz in Single-Layer Graphene, <em>ACS Photonics</em>, 10, 3171–3180 (2023).</span>
 </li>
 <li style="margin-bottom: 0.8em; display: flex;">
 <span style="width: 2.5em; flex-shrink: 0;">[2]</span>
 <span>A. Di Gaspare et al., All in one-chip, electrolyte-gated graphene amplitude modulator, saturable absorber mirror and metrological frequency-tuner in the 2–5 THz range, <em>Adv. Optical Mater.</em>, 10, 2200819 (2024).</span>
 </li>
 <li style="margin-bottom: 0.8em; display: flex;">
 <span style="width: 2.5em; flex-shrink: 0;">[3]</span>
 <span>H. A. Hafez et al., Extremely efficient terahertz high-harmonic generation in graphene by hot Dirac fermions, <em>Nature</em>, vol. 561, no. 7724, pp. 507–511 (2018).</span>
 </li>
 <li style="margin-bottom: 0.8em; display: flex;">
 <span style="width: 2.5em; flex-shrink: 0;">[4]</span>
 <span>J. Stensberg et al., Observation of terahertz second harmonic generation from Dirac surface states in the topological insulator Bi<sub>2</sub>Se<sub>3</sub>, <em>Phys. Rev. B</em>, vol. 109, no. 24, p. 245112 (2024).</span>
 </li>
 <li style="margin-bottom: 0.8em; display: flex;">
 <span style="width: 2.5em; flex-shrink: 0;">[5]</span>
 <span>A. Di Gaspare et al., Compact terahertz harmonic generation in the Reststrahlenband using a graphene-embedded metallic split ring resonator array, <em>Nature Commun.</em>, vol. 15, no. 1, p. 2312 (2024).</span>
 </li>
 <li style="margin-bottom: 0.8em; display: flex;">
 <span style="width: 2.5em; flex-shrink: 0;">[6]</span>
 <span>A. Di Gaspare et al., Second and third harmonic generation in topological insulator-based van der Waals metamaterials, <em>Nature Light: Science & Applications</em> (in press, 2025).</span>
 </li>
 <li style="margin-bottom: 0.8em; display: flex;">
 <span style="width: 2.5em; flex-shrink: 0;">[7]</span>
 <span>A. Di Gaspare et al., Electrically-driven heterostructured wire lasers with integrated graphene plasmons, <em>Nature Nanotechnology</em> (in press, 2025).</span>
 </li>
 </ul>
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Last modified: Nov 30, 2025, 7:35:30 AM