Second harmonic generation from metallic arrays of rectangular holes

The generation process of second harmonic (SH) radiation from holes periodically arranged on a metal surface is investigated. Three main modulating factors affecting the optical response are identified: the near-field distribution at the wavelength of the fundamental harmonic, how SH light couples to the diffraction orders of the lattice, and its propagation properties inside the holes. It is shown that light generated at the second harmonic can excite electromagnetic modes otherwise inaccessible in the linear regime under normal incidence illumination. It is demonstrated that the emission of SH radiation is only allowed along off-normal paths precisely due to that symmetry. Two different regimes are studied in the context of extraordinary optical transmission, where enhanced linear transmission either occurs through localized electromagnetic modes or is aided by surface plasmon polaritons (SPPs). While localized resonances in metallic hole arrays have been previously investigated, the role played by SPPs in SH generation has not been addressed so far. In general, good agreement is found between our calculations (based on the finite difference time domain method) and the experimental results on localized resonances, even though no free fitting parameters were used in describing the materials. It is found that SH emission is strongly modulated by enhanced fields at the fundamental wavelength (either localized or surface plasmon modes) on the glass metal interface. This is so in the transmission side but also in reflection, where emission can only be explained by an efficient tunneling of SH photons through the holes from the output to the input side. Finally, the existence of a dark SPP at the fundamental field is identified through a noninvasive method for the first time, by analyzing the efficiency and far-field pattern distribution in transmission at the second harmonic.Comment: This paper was published in JOSA B and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/josab/abstract.cfm?URI=josab-32-1-15. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under la

Solving differential equations with Deep Learning: a beginner's guide

The research in Artificial Intelligence methods with potential applications in science has become an essential task in the scientific community last years. Physics Informed Neural Networks (PINNs) is one of this methods and represent a contemporary technique that is based on the fundamentals of neural networks to solve differential equations. These kind of networks have the potential to improve or complement classical numerical methods in computational physics, making them an exciting area of study. In this paper, we introduce PINNs at an elementary level, mainly oriented to physics education so making them suitable for educational purposes at both undergraduate and graduate levels. PINNs can be used to create virtual simulations and educational tools that aid in understating complex physical concepts and processes where differential equations are involved. By combining the power of neural networks with physics principles, PINNs can provide an interactive and engaging learning experience that can improve students' understanding and retention of physics concepts in higher education

Evaluation of non-ohmic losses with overlap integrals

2 pages, 1 figure.In the main text of the paper corresponding to the present document, WPP--SPP conversion devices are considered. Reflection and radiation losses in such structures are evaluated by means of overlap integrals. In this Auxiliary Material section details of such procedure are provided.Peer reviewe

Non-local quantum effects in plasmons of graphene superlattices

By using a non-local, quantum mechanical response function we study graphene plasmons in a one-dimensional superlattice (SL) potential $V_0 \cos G_0x$. The SL introduces a quantum energy scale $E_G \sim \hbar v_F G_0$ associated to electronic sub-band transitions. At energies lower than $E_G$, the plasmon dispersion is highly anisotropic; plasmons propagate perpendicularly to the SL axis, but become damped by electronic transitions along the SL direction. These results question the validity of semiclassical approximations for describing low energy plasmons in periodic structures. At higher energies, the dispersion becomes isotropic and Drude-like with effective Drude weights related to the average of the absolute value of the local chemical potential. Full quantum mechanical treatment of the kinetic energy thus introduces non-local effects that delocalize the plasmons in the SL, making the system behave as a meta-material even near singular points where the charge density vanishes.Comment: 22 pages, 14 figure

Influence of material properties on extraordinary optical transmission through hole arrays

We present a theoretical study, based on the finite difference time domain method, of the optical response of circular hole arrays drilled in several metal films (Ag, Au, Cu, Al, Ni, Cr, and W). Two series of structures are studied. In the first one, transmittance peaks are analyzed as all geometrical parameters defining the system are scaled, except for the metal thickness which is kept constant, showing good agreement with existing experimental data. In the second series, the metal thickness is also scaled. This allows a clear distinction in the behavior of different metals: Ag, Au, and Cu show even larger transmittance peaks than hole arrays in a perfect conductor with the same nominal parameters. This is due to both a larger effective hole area and smaller absorption. In the case of Ni and Cr, the transmittance is much smaller due to absorption. Band structure calculations confirm that surface electromagnetic modes sustained by the perforated metal film are responsible for the extraordinary optical transmission phenomenon

Guiding and Focusing of Electromagnetic Fields with Wedge Plasmon Polaritons

We study theoretically electromagnetic modes guided by metallic wedges at telecom wavelengths. These modes are found to exhibit superior confinement while showing similar propagation loss as compared to other subwavelength guiding configurations. It is also shown that mode focusing can be realized by gradual modification of the wedge geometry along the mode propagation direction

Dissipation-driven generation of two-qubit entanglement mediated by plasmonic waveguides

We study the generation of entanglement between two distant qubits mediated by the surface plasmons of a metallic waveguide. We show that a V-shaped channel milled in a flat metallic surface is much more efficient for this purpose than a metallic cylinder. The role of the misalignments of the dipole moments of the qubits, an aspect of great importance for experimental implementations, is also studied. A careful analysis of the quantum-dynamics of the system by means of a master equation shows that two-qubit entanglement generation is essentially due to the dissipative part of the effective qubit-qubit coupling provided by the surface plasmons. The influence of a coherent external pumping, needed to achieve a steady state entanglement, is discussed. Finally, we pay attention to the question of how to get information experimentally on the degree of entanglement achieved in the system.Comment: 13 pages, 12 figure

Theory of light transmission through an array of rectangular holes

In a two-dimensional array of rectangular holes perforated on a metallic film, two mechanisms leading to enhanced transmission of light operate: excitation of surface plasmon polaritons (SPPs) and localized resonances that are also present in single holes. In this paper, we analyze theoretically how the two mechanisms evolve and mix when the period of the array is varied. We also demonstrate that absorption in the metal is the main limiting factor for the SPP-based enhanced transmission

Anthocyanin Pigments: Importance, Sample Preparation and Extraction

Anthocyanins are naturally occuring pigments belonging to the group of flavonoids, a subclass of the polyphenol family. They are common components of the human diet, as they are present in many foods, fruits and vegetables, especially in berries and red wine. There were more studies conducted on effect of processing and storage on changes and stability of colors of anthocyanins in foods such as fruits and also for their use as natural colorants. Besides, the interest on anthocyanins is still growing also owing to their strong antioxidant activity against many chronic diseases, numerous studies about their medicinal, therapeutical and nutritional value were also conducted. There are pieces of evidence regarding the positive association of their intake with healthy biological effects. They act as antioxidants both in the foodstuffs in which they are found and in the organism that take in foods rich in anthocyanins. Many efforts have been carried out to develop new analytical techniques for identification and quantification of anthocyanins in plant materials, as well as their effects in vivo and in vitro. With this in mind, an overview to general considerations concerning (i) polyphenol and flavonoid history; (ii) chemical structure, color and intake of anthocyanins and (iii) sample preparation and extraction methods are presented in this chapter