Open Access
Thermal emission in temporal metamaterials: fundamentals and novel phenomena
(IEEE, 2023) Vázquez Lozano, Juan Enrique; Liberal Olleta, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
Thermal emission is a fundamental issue that customarily has been fueled by the developments carried out in nanophotonics. Given such a parallelism and the latest advances bringing forward the realization of temporal metamaterials, in this work we combine both topics to sketch out an original theoretical formulation for rigorously addressing thermal emission in time-modulated media. Upon this ground, we find new physics and thermal phenomena, highlighting the emergence of non-local correlations, the possibility to overcome the black-body spectrum by temporal means, as well as the role of ENZ bodies as genuine platforms to enhance thermal emission, and the conception of innovative thermal emitters dual to spatial gratings.
Open Access
Synthesis and raman detection of 5-amino-2-mercaptobenzimidazole self-assembled monolayers in nanoparticle-on-a-mirror plasmonic cavity driven by dielectric waveguides
(American Chemical Society, 2024) Redolat, Javier; Camarena-Pérez, María; Griol, Amadeu; Sinusia Lozano, Miguel; Gómez-Gómez, María Isabel; Vázquez Lozano, Juan Enrique; Miele, Ermanno; Baumberg, Jeremy J.; Martínez, Alejandro; Pinilla-Cienfuegos, Elena; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
Functionalization of metallic surfaces by molecular monolayers is a key process in fields such as nanophotonics or biotechnology. To strongly enhance light-matter interaction in such monolayers, nanoparticle-on-a-mirror (NPoM) cavities can be formed by placing metal nanoparticles on such chemically functionalized metallic monolayers. In this work, we present a novel functionalization process of gold surfaces using 5-amino-2-mercaptobenzimidazole (5-A-2MBI) molecules, which can be used for upconversion from THz to visible frequencies. The synthesized surfaces and NPoM cavities are characterized by Raman spectroscopy, atomic force microscopy (AFM), and advancing-receding contact angle measurements. Moreover, we show that NPoM cavities can be efficiently integrated on a silicon-based photonic chip performing pump injection and Raman-signal extraction via silicon nitride waveguides. Our results open the way for the use of 5-A-2MBI monolayers in different applications, showing that NPoM cavities can be effectively integrated with photonic waveguides, enabling on-chip enhanced Raman spectroscopy or detection of infrared and THz radiation.
Open Access
Incandescent temporal metamaterials
(Nature Research, 2023) Vázquez Lozano, Juan Enrique; Liberal Olleta, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
Regarded as a promising alternative to spatially shaping matter, time-varying media can be seized to control and manipulate wave phenomena, including thermal radiation. Here, based upon the framework of macroscopic quantum electrodynamics, we elaborate a comprehensive quantum theoretical formulation that lies the basis for investigating thermal emission effects in time-modulated media. Our theory unveils unique physical features brought about by time-varying media: nontrivial correlations between fluctuating electromagnetic currents at different frequencies and positions, thermal radiation overcoming the black-body spectrum, and quantum vacuum amplification effects at finite temperature. We illustrate how these features lead to striking phenomena and innovative thermal emitters, specifically, showing that the time-modulation releases strong field fluctuations confined within epsilon-near-zero (ENZ) bodies, and that, in turn, it enables a narrowband (partially coherent) emission spanning the whole range of wavevectors, from near to far-field regimes.
Open Access
Review on the scientific and technological breakthroughs in thermal emission engineering
(American Chemical Society, 2024) Vázquez Lozano, Juan Enrique; Liberal Olleta, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The emission of thermal radiation is a physical process of fundamental and technological interest. From different approaches, thermal radiation can be regarded as one of the basic mechanisms of heat transfer, as a fundamental quantum phenomenon of photon production, or as the propagation of electromagnetic waves. However, unlike light emanating from conventional photonic sources, such as lasers or antennas, thermal radiation is characterized for being broadband, omnidirectional, and unpolarized. Due to these features, ultimately tied to its inherently incoherent nature, taming thermal radiation constitutes a challenging issue. Latest advances in the field of nanophotonics have led to a whole set of artificial platforms, ranging from spatially structured materials and, much more recently, to time-modulated media, offering promising avenues for enhancing the control and manipulation of electromagnetic waves, from far- to near-field regimes. Given the ongoing parallelism between the fields of nanophotonics and thermal emission, these recent developments have been harnessed to deal with radiative thermal processes, thereby forming the current basis of thermal emission engineering. In this review, we survey some of the main breakthroughs carried out in this burgeoning research field, from fundamental aspects to theoretical limits, the emergence of effects and phenomena, practical applications, challenges, and future prospects.
Open Access
Quantum antireflection temporal coatings: quantum state frequency shifting and inhibited thermal noise amplification
(wiley, 2023) Liberal Olleta, Íñigo; Vázquez Lozano, Juan Enrique; Pacheco-Peña, Víctor; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
The quantum optical response of antireflection temporal coatings (ATCs), that is, matching temporal layers that suppress the generation of backward waves in temporal boundaries, is investigated. The results reveal that quantum ATCs are characterized for inducing a frequency shift of the quantum state, while preserving all photon statistics intact. Thus, they can find application for fast quantum frequency shifting in photonic quantum networks. The quantum theory also provides additional insight on their classical mode of operation, clarifying which quantities are preserved through the temporal boundary. Last, it is shown that quantum ATCs allow for fast temporal switching without amplification of thermal fields.
Open Access
Spatiotemporal symmetries and energy-momentum conservation in uniform spacetime metamaterials
(American Chemical Society, 2024-11-13) Liberal Olleta, Íñigo; Ganfornina Andrades, Antonio; Vázquez Lozano, Juan Enrique; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Spacetime metamaterials are opening new regimes of light-matter interactions based on the breaking of temporal and spatial symmetries, as well as intriguing concepts associated with synthetic motion. In this work, we investigate the continuous spatiotemporal translation symmetry of spacetime metamaterials with uniform modulation velocity. Using Noether's theorem, we demonstrate that such symmetry entails the conservation of the energy momentum. We highlight how energy-momentum conservation imposes constraints on the range of allowed light-matter interactions within spacetime metamaterials, as illustrated with examples of the collision of electromagnetic and modulation pulses. Furthermore, we discuss the similarities and differences between the conservation of energy-momentum and relativistic effects. We believe that our work provides a step forward in clarifying the fundamental theory underlying spacetime metamaterials.
Embargo
Dispersion effects in thermal emission from temporal metamaterials: high-frequency cutoffs
(Optica, 2025-02-03) Vertiz Conde, Amaia; Liberal Olleta, Íñigo; Vázquez Lozano, Juan Enrique; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The latest breakthroughs in time-varying photonics are fueling novel, to the best of our knowledge, thermal emission phenomena, e.g., showing that the dynamic amplification of quantum vacuum fluctuations, induced by the time modulation of material properties, enables a mechanism to surpass the blackbody spectrum. So far, this issue has only been investigated under the assumption of non-dispersive time modulations. In this work, we identify the existence of a nonphysical diverging behavior in the time-modulated emission spectra at high frequencies and prove that it is actually attributed to the simplistic assumption of a non-dispersive (temporally local) response of the time modulation associated with memory-less systems. Accordingly, we upgrade the theoretical formalism by introducing a dispersive response function, showing that it leads to a high-frequency cutoff, thereby eliminating the divergence and hence allowing for the proper computation of the emission spectra of time-modulated materials.
Open Access
Quantum vacuum amplification in time-varying media with arbitrary temporal profiles
(American Physical Society, 2024-12-26) Ganfornina Andrades, Antonio; Vázquez Lozano, Juan Enrique; Liberal Olleta, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
In this work we address quantum vacuum amplification effects in time-varying media with an arbitrary time-modulation profile. To this end, we propose a theoretical formalism based on the concept of conjugated harmonic oscillators, evaluating the impact on the transition time in temporal boundaries, shedding light into the practical requirements to observe quantum effects at them. In addition, we find nontrivial effects in pulsed modulations, where the swiftest and strongest modulation does not lead to the highest photon production. Thus, our results provide key insights for the design of temporal modulation sequences to enhance quantum phenomena.
Open Access
Tutorial on the conservation of momentum in photonic time-varying media [Invited]
(Optica, 2023) Ortega Gómez, Ángel; Lobet, Michaël; Vázquez Lozano, Juan Enrique; Liberal Olleta, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
Time-varying media break temporal symmetries while preserving spatial symmetries intact. Thus, it represents an excellent conceptual framework to investigate the fundamental implications of Noether’s theorem for the electromagnetic field. At the same time, addressing momentum conservation in time-varying media sheds light on the Abraham-Minkowski debate, where two opposing forms of the electromagnetic field momentum are defended. Here, we present a tutorial review on the conservation of momentum in time-varying media. We demonstrate that the Minkowski momentum is a conserved quantity with three independent approaches of increasing complexity: (i) via the application of the boundary conditions for Maxwell equations at a temporal boundary, (ii) testing for constants of motion and deriving conservation laws, and (iii) applying temporal and spatial translations within the framework of the Lagrangian theory of the electromagnetic field. Each approach provides a different and complementary insight into the problem.
Open Access
Symmetries in time-varying media: on the conservation of spin angular momentum, helicity, and chirality
(IEEE, 2024) Mohammadi Jajin, Mohsen; Vázquez Lozano, Juan Enrique; Liberal Olleta, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
Our results demonstrate that time-varying media exacerbate the differences between the symmetries and conserved quantities associated with dynamical properties associated with the circular polarization of light. In this manner, we provide further insights into the physical meaning of helicity and chirality, including their similarities and differences, as well as the fundamental role played by the symmetries of the electromagnetic Lagrangian in time-varying media.