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

Cálculo de la demora en carreteras convencionales mediante lógica fuzzy

La demora de vehículos es uno de los principales factores para determinar el nivel de servicio de una carretera convencional. La determinación de un método que permita calcularlo con fiabilidad para todos los conductores es materia de numerosos estudios, debido a la gran cantidad de factores, y a las diferencias entre conductores debido a la percepción subjetiva de estos factores. En este trabajo se ha diseñado un sistema de cálculo de demoras mediante el uso de técnicas de razonamiento aproximado a través de lógica fuzzy. De este modo se ha podido tratar adecuadamente la subjetividad de los conductores a la hora de calcular la demora independiente de cada vehículo. El sistema diseñado se divide en siete subsistemas fuzzy que calculan la calidad del entorno, el coche y el conductor, a partir de los cuales calcula el nivel de seguridad mediante otro subsistema fuzzy. Posteriormente utiliza esta información para calcular, mediante otros subsistemas fuzzy, si el espacio disponible para adelantar es suficiente, si el conductor considera posible adelantar y si desea adelantar. Finalmente se ha propuesto un nuevo sistema de clasificación de vehículos demorados que utiliza los datos de posibilidad y deseo de adelantar calculados anteriormente para determinar el estado del vehículo. Todos estos cálculos se realizan a partir de medidas externas relativas al entorno, al conductor, al coche y a la circulación. Para probar este sistema se realizaron encuestas a diferentes usuarios de carreteras convencionales y se compararon sus respuestas con las del sistema, obteniendo coincidencias en un más de un 90% de los casos. Se concluye que el nuevo enfoque fuzzy que se ha aportado al cálculo de la demora es efectivo y capaz de tratar la subjetividad que no se podía tratar con métodos tradicionales. [ABSTRACT] Car delay is one of the main factors used to calculate the level of service on rural highways. To establish a method which allows a faithful calculation for every driver is the subject of many researchs, because of the very different factors and the differences between the different subjective perceptions drivers have. In this work a system for the calculation of car delays has been developed using approximate reasoning with fuzzy logic. This way, drivers subjectivity has been managed when calculating individual car delays. The system is divided into seven fuzzy subsystems that calculate the quality of the environment, the car and the driver, and uses this qualities to calculate the level of safety using another fuzzy system. Then, this information is used to work out, by means of other fuzzy systems, if the gap available to overtake is enough, if the driver thinks he can overtake and if the driver wants to overtake. Finally a new system of clasification for delayed vehicles has been proposed. This proposed system uses the posibility and willing of overtaking data previously calculated to determine the state of the vehicle. All this calculations are made from external measurements related to car, environment, driver and traffic. Some surveys were made to several users of rural highways to test the system. Their answers were compared with system answers, being the same on a 90% of the answers. In conclusion, the new fuzzy approach given for the calculation of delay is effective, and is able to manage subjectivity, which was unable to manage with traditional methods

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

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

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

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

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