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Controlling the coherence properties of rare earth emitters in solid-state platforms in the absence of an optical cavity is highly desirable for quantum light-matter interfaces and photonic networks. Here, we demonstrate the possibility of generating directional and spatially coherent light from Nd3+ ions coupled to the longitudinal plasmonic mode of a chain of interacting Ag nanoparticles. The effect of the plasmonic chain on the Nd3+ emission is analyzed by Fourier microscopy. The results reveal the presence of an interference pattern in which the Nd3+ emission is enhanced at specific directions, as a distinctive signature of spatial coherence. Numerical simulations corroborate the need of near-field coherent coupling of the emitting ions with the plasmonic chain mode. The work provides fundamental insights for controlling the coherence properties of quantum emitters at room temperature and opens new avenues towards rare earth based nanoscale hybrid devices for quantum information or optical communication in nanocircuits.

Estudiamos diversos minerales encontrados en la fracción magnética de arcillas de sedimentos medicinales recolectados en dos lagunas peruanas, La Milagrosa (MML) y La Mellicera (MELL). La fracción de arcilla se separó por el método de sedimentación. Las técnicas analíticas físicas que utilizamos fueron la fluorescencia de rayos X por energía dispersiva (FRXED), la difractometría de rayos X (DRX) y la espectroscopía Mössbauer de transmisión (EMT). Éstas técnicas las complementamos con un análisis físico-químico para determinar la textura, pH y conductividad eléctrica de las muestras recolectadas. Así, hemos observado, a través de DRX, minerales como ilita, calcita y maghemita. Específicamente, para MML, por DRX observamos dos fases minerales: cuarzo y dolomita. La EMT nos permitió observar la fracción magnética de los sedimentos. En los espectros observamos cuatro sextetos magnéticos y tres dobletes paramagnéticos. Los sextetos fueron asignados a hematita/goethita, dos sitios de magnetita (Fe3+ y Fe2.5+) y maghemita. Asimismo, los dobletes se asignaron a Fe2+ y Fe+3, sitios asignados a ilita y pirita, respectivamente

Deep learning has become the dominant approach in artificial intelligence to solve complex data-driven problems. Originally applied almost exclusively in computer-science areas such as image analysis and nature language processing, deep learning has rapidly entered a wide variety of scientific fields including physics, chemistry and material science. Very recently, deep neural networks have been introduced in the field of nanophotonics as a powerful way of obtaining the nonlinear mapping between the topology and composition of arbitrary nanophotonic structures and their associated functional properties. In this paper, we have discussed the recent progress in the application of deep learning to the inverse design of nanophotonic devices, mainly focusing on the three existing learning paradigms of supervised-, unsupervised-, and reinforcement learning. Deep learning forward modelling i.e. how artificial intelligence learns how to solve Maxwell’s equations, is also discussed, along with an outlook of this rapidly evolving research area.

16 pags., 9 figs., Weyl photons appear when two three-dimensional photonic bands with linear dispersion are degenerate at a single momentum point, labeled as Weyl point. These points have remarkable properties such as being robust topological monopoles of Berry curvature as well as an associated vanishing density of states. In this work, we report on a systematic theoretical study of the quantum optical consequences of such Weyl photons. First, we analyze the dynamics of a single quantum emitter coupled to a Weyl photonic bath as a function of its detuning with respect to the Weyl point and study the corrresponding emission patterns, using both perturbative and exact treatments. Our calculations show an asymmetric dynamical behavior when the emitter is detuned away from the Weyl frequency, as well as different regimes of highly collimated emission, which ultimately translate in a variety of directional collective decays. Besides, we find that the incorporation of staggered mass and hopping terms in the bath Hamiltonian both enriches the observed phenomenology and increases the tunabilit., A.G.-T. acknowledges support from CSIC Research Platform on Quantum Technologies PTI-001 and from Spanish Project No. PGC2018-094792-B-100(MCIU/AEI/FEDER, EU). J.B.-A. and I.G.-E. acknowledge financial support from the Spanish Ministry for Science, Innovation, and Universities through grants RTI2018-098452-B-I00 (MCIU/AEI/FEDER,UE), the “María de Maeztu” programme for Units of Excellence in R&D (MDM-2014-0377 and CEX2018-000805-M), and FPU Grant No. AP-2018-02748.

6 pags., 4 figs., Long-range coherent interactions between quantum emitters are instrumental for quantum information and simulation technologies, but they are generally difficult to isolate from dissipation. Here, we show how such interactions can be obtained in photonic Weyl environments due to the emergence of an exotic bound state whose wave function displays power-law spatial confinement. Using an exact formalism, we show how this bound state can mediate coherent transfer of excitations between emitters, with virtually no dissipation and with a transfer rate that follows the same scaling with distance as the bound state wave function. In addition, we show that the topological nature of Weyl points translates into two important features of the Weyl bound state, and, consequently, of the interactions it mediates: first, its range can be tuned without losing the power-law confinement, and, second, they are robust under energy disorder of the bath. To our knowledge, this is the first proposal of a photonic setup that combines simultaneously coherence, tunability, long range, and robustness to disorder. These findings could ultimately pave the way for the design of more robust long-distance entanglement protocols or quantum simulation implementations for studying long-range interacting systems., We acknowledge financial support from the Spanish MCIU under Grant No. RTI2018-098452-B-I00 (MCIU/ AEI/FEDER, UE) and the “María de Maeztu” programme for Units of Excellence in R&D (MDM-2014-0377 and CEX2018-000805-M). A. G. T. acknowledges support from CSIC Research Platform on Quantum Technologies PTI-001 and from Spanish project PGC2018-094792-B100 (MCIU/AEI/FEDER, EU). I. G. E. acknowledges financial support from the Ministry of Science and`Innovation of Spain (FPU Grant No. AP-2018-02748)

New York, NY, USA, 27 Sept.-3 Oct. 2020, We investigate the quantum optical behavior of quantum emitters coupled to a Weyl-like photonic environment. For the single emitter case, we will report on the formation of a novel photon-atom bound state featuring a tunable power-law localization of the excitation around the emitter. When two emitters are considered we show that the emergent bound state can mediate tunable and robust long-range coherent interactions., We acknowledge financial support from the Spanish MCIU under grant RTI2018-098452-B-I00 (MCIU/AEI/FEDER, UE) and the “Marıa de Maeztu” programme for Units of Excellence in R&D (MDM-2014-0377 and CEX2018-000805- M). AGT acknowledges support from CSIC Research Plat form on Quantum Technologies PTI-001 and from Spanish project PGC2018-094792-B-100 (MCIU/AEI/FEDER, EU). IGE acknowledges financial support from the Ministry of Science and Innovation of Spain (FPU grant AP-2018-027).

Se ha estudiado una muestra del meteorito de Tuxtuac, clasicada como una condrita ordinaria. Se aplicaron tres técnicas analíticas. Así, la uorescencia de rayos X por dispersión de energía nos permitió identicar hierro, níquel y cobalto, que forman la estructura de los minerales kamacita y taenita. Asimismo, la difractometr ía de rayos X nos permitió reconocer la presencia de las fases estructurales de los silicatos olivino, piroxeno y ortopiroxeno. Además, la espectroscopia Mössbauer de transmisión con 57Fe indicó la presencia de dos sextetos magnéticos. Uno fue asignado a troilita y el otro, a goethita. Después del proceso de separación magnética, esta misma técnica se utilizó para determinar información más detallada sobre los minerales magnéticos presentes en la muestra. Como resultado, en los respectivos espectros Mössbauer se obtuvieron otros dos sextetos magnéticos, asignados a kamacita y taenita, respectivamente. Además, la presencia de goethita en la muestra puede ser el resultado de la meteorización química.

Weyl nodes are band degeneracy points with relativistic dispersion and topological properties arising in certain three-dimensional periodic systems with broken parity-time symmetry. Despite their fundamental importance, the intrinsic accidental nature of Weyl nodes makes the general endeavor of finding them a challenging task. In this work, we show how Weyl nodes can be generated in cubic crystal structures with a single orbital per site based on a systematic approach that combines a tight-binding analysis with general principles which can be applied to both fermionic and bosonic systems. The cubic Weyl systems generated here preserve time-reversal symmetry but break inversion symmetry hosting the minimum four Weyl points allowed. Laser assisted hopping techniques on cubic optical lattices can allow the artificial generation of such Weyl semimetals. Magnetic oscillation experiments can be used to probe the Weyl orbits along the Fermi arcs on opposite sides of the sample connected through the bulk Weyl nodes.

Significance Optically pumped far-infrared (OPFIR) lasers are one of the most powerful continuous-wave terahertz sources. However, such lasers have long been thought to have intrinsically low efficiency and large sizes. Moreover, all previous theoretical models failed to predict even qualitatively the experimental performance at high pressures. Here, we have developed an innovative model that captures the full physics of the lasing process and correctly predicts the behavior in the high-pressure regime. Validated against experiments, our model shows that nearly all previous OPFIR lasers were operating in the wrong regime and that 10 × greater efficiency is possible by redesigning the terahertz cavity. Our results reintroduce the use of OPFIR lasers as a powerful and compact source of terahertz radiation.

La teoría que Bohr aplicó en 1913 para describir los orbitales electrónicos se extiende al caso de los orbitales de muones en un átomo muónico. Cabe la posibilidad que para nucleídos con número atómico suficientemente grande, estas órbitas ocupen el volumen nuclear y, por lo tanto, el modelo de núcleo puntual que Bohr utilizó ya no es aplicable. Este estudio deduce que para nucleídos con Z ≥ 46 el radio de la primera órbita de Bohr yace dentro del volumen nuclear; asimismo, se deduce que las órbitas muónicas de orden mayor yacen fuera del volumen nuclear., The theory that Bohr applied in 1913 to describe the electronic orbitals is extended to the muonic orbitals in a muonic atom. There is a possibility that for nuclides with sufficiently large atomic number, these orbitals occupy the nuclear volume and, therefore, the puntual nuclear model that Bohr utilized is not applicable. In this study, we deduce that for nuclides with Z ≥ 46 the Bohr radius of the first level stay inner of nuclear volume; also, we deduce that the muonic orbitals with bigger order stay out of nuclear volume.

It is shown that lasing action at subwavelength scales can be achieved in realistic plasmonic systems supporting long-range surface plasmons (LRSPPs). To this end, a general numerical framework has been developed that is able to accurately account for the full spatio-temporal lasing dynamics and the vastly different length- and time-scales featured by this class of systems. Starting from a loss compensation regime for propagating LRSPPs, it is shown how the introduction of an optical feedback mechanism induces the formation of a self-sustained laser oscillation at moderate pump intensities. The simplicity of the proposed subwavelength scale laser offers significant potential as a novel class of planar light sources in complex plasmonic circuits.

We study theoretically nonlinear propagation of light in a graphene monolayer. We show that the large intrinsic nonlinearity of graphene at optical frequencies enables the formation of quasi one-dimensional self-guided beams (spatial solitons) featuring subwavelength widths at moderate electric-field peak intensities. We also demonstrate a novel class of nonlinear self-confined modes resulting from the hybridization of surface plasmon polaritons with graphene optical solitons.

In this paper, we review various numerical methods currently used to model nonlinear optical processes in nanophotonics. Among the different theoretical frameworks that have been used to study nonlinear photonic structures, we particularly focus on the application of both perturbation theory and coupled-mode theory to the analysis of complex nonlinear nanophotonic devices. This description is illustrated on several examples of how these techniques can be used to design photonic-crystal-based nonlinear devices. In addition, in all these examples, we show that the predictions made by the two mentioned techniques are in a good agreement with the numerical results obtained from a nonlinear finite-difference-time-domain approach to these problems.

We present our recent advances in nanoscale lasing action enabled by plasmonic resonances. First, we study lasing action in plasmonic crystals incorporating optically pumped four-level gain media. We show that the excitation of dark plasmonic resonances (via the gain medium) enables accessing the optimal lasing characteristics of this class of systems. Second, we analyze the conditions for the emergence of self-sustained laser oscillations in an optically-pumped long-range surface-plasmon structure that includes plasmonic Bragg mirrors as optical feedback mechanism.

We theoretically investigate lasing action in plasmonic crystals incorporating optically pumped four-level gain media. By using detailed simulations based on a time-domain generalization of the finite-element method, we show that the excitation of dark plasmonic resonances (via the gain medium) enables accessing the optimal lasing characteristics of the considered class of systems. Moreover, our study reveals that, in general, arrays of nanowires feature lower lasing thresholds and larger slope efficiencies than those corresponding to periodic arrays of subwavelength apertures. These findings are of relevance for further engineering of active devices based on plasmonic crystals

We theoretically study the emergence of strong coupling in the interaction between quantum emitters and the localized surface plasmons of a metal nanoparticle. Owing to their quasidegenerate nature, the continuum of multi-poles is shown to behave as a pseudomode strongly coupled to single emitters instead of as a Markovian bath. We demonstrate that the corresponding capping of the induced loss rate enables collective strong coupling to the dipole mode. Numerical simulations and analytical modeling are applied to several configurations of increasing complexity to grasp the relevant physics. In particular, the emitters closest to the nanoparticle surface are proven to contribute the most to the build-up of the plasmon-exciton polaritons, in contrast with the weak-coupling picture of quenching.

El propósito de este trabajo fue la identificación y la caracterización de los principales minerales en las fracciones arcilla de muestras de suelos tropicales que fueron seleccionadas de la Reserva Forestal de la Universidad Agraria de la Selva, localizada en la Región de Huánuco, Perú, con énfasis en el estudio de los sesquióxidos de hierro (óxidos, hidróxidos y oxidróxidos de hierro) y minerales de arcilla con sustitución de hierro. Se utilizó el método químico de disolución selectiva utilizando ditionito-citrato-bicarbonato, DCB, [1] para la disolución de óxidos de hierro cristalinos, lo cual favorece la identificación de minerales de arcilla. Asimismo fueron utilizadas las técnicas analíticas de difractometría de rayos X, DRX, y espectroscopia Mössbauer por transmisión, EMT, a temperatura ambiente, TA, y a 110 K para determinar la composición mineralógica de las muestras. En este artículo presentamos solo los resultados obtenidos con dos muestras seleccionadas por sus características contrastantes.

Photonic crystals can control the flow of light but they are extremely sensitive to structural disorder. Although this often degrades performance, disorder can actually be used to enhance light collimation.

We theoretically investigate how phase-only spatial light modulation can enable controlling and focusing the second-harmonic light generated in transparent nonlinear random structures. The studied structures are composed of domains with random sizes and antiparallel polarization, which accurately model widely used ferroelectric crystals such as strontium barium niobate. Using a first-principles Green-function formalism, we account for the effect that spatial light modulation of the fundamental beam introduces into the second-order nonlinear frequency conversion occurring in the considered class of structures. This approach provides a complete description of the physical origin of the second-harmonic light generation in the system, as well as the optimization of the light intensity in any arbitrary direction. Our numerical results show how the second-harmonic light is influenced by both the disorder in the structure and the boundaries of the crystal. Particularly, we find that the net result from the interplay between disorder and boundary effects is strongly dependent on the dimensions of the crystal and the observation direction. Remarkably, our calculations also show that although in general the maximum possible enhancement of the second-order light is the same as the one corresponding to linear light scattering in turbid media, in the Cerenkov phase matching direction the enhancement can exceed the linear limit. The theoretical analysis presented in this work expands the current understanding of light control in complex media and could contribute to the development of a new class of imaging and focusing techniques based on nonlinear frequency mixing in random optical materials, We acknowledge the Ministerio de Economía y Competitividad which supported the work under GrantsNo.MAT2011- 28665, No. IPT-120000-2010-29, and No. CSD2007-00046. F.J.R. acknowledges support by the Juan de la Cierva program, Grant No. JCI-2009-04860. J.B.A. acknowledges financial support by the Ramon-y-Cajal program, Grant No. RyC-2009- 05489

et al., We theoretically investigate the amplification of extraordinary optical transmission (EOT) phenomena in periodic arrays of subwavelength apertures incorporating gain media. In particular, we consider a realistic structure consisting of an opaque silver film perforated by a periodic array of slits and clad on each side by an optically pumped dielectric thin film containing rhodamine dye molecules. By solving the semiclassical electronic rate equations coupled to rigorous finite-element simulations of the electromagnetic fields, we show how the resonant electric-field enhancement associated with EOT properties enables complete ohmic loss compensation at moderate pump intensity levels. Furthermore, our calculations show that, as a consequence of the strong spatial hole-burning effects displayed by the considered structures, three separate regimes of operation arise: the system can behave as an absorber, an optical amplifier or a laser, depending on the value of the pump intensity. A discussion on the feasibility of reaching the lasing regime in the considered class of structures is also presented. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft., This work was sponsored by the Spanish Ministry of Science and Innovation under the projects MAT2009-06609-C02 and CSD2007-046-NanoLight and by the Ramón-y-Cajal program (grant no. RyC-2009-05489).

In this chapter, we describe a physical picture of nonlinear frequency mixing processes in resonant cavities inspired on a classical analog of the quantum Purcell effect. Applying this general framework to one particularly important system, we show how this approach allows identifying the optimal conditions enabling low-power efficient terahertz (THz) generation via nonlinear frequency mixing. We also address the practical implementation of these general principles. Using a detailed numerical analysis, we demonstrate how the unique properties of photonic crystals to achieve simultaneous spectral and spatial electromagnetic mode engineering enable a dramatic reduction of the pump powers required to reach quantum-limited THz conversion efficiencies using realistic nonlinear optical material systems.

We show that the weak second harmonic light generated from a random distribution of nonlinear domains of transparent Strontium Barium Niobate crystals can display a particularly intense generation in the forward direction. By using a theoretical model able to analyze the optical response of arbitrary distributions of three-dimensional nonlinear volumes of any shape, we found that the physical origin of this observation can be explained in terms of the scattering of light by a single nonlinear domain.

The second-harmonic generation from transparent strontium-barium niobate crystals is experimentally studied and explained from the emission patterns of randomly scattered nonlinear domains and the far field interference of the light generated from such domains.

We propose a scheme for efficient cavity-enhanced nonlinear THz generation via difference-frequency generation (DFG) processes using a triply resonant system based on photonic crystal cavities. We show that high nonlinear overlap can be achieved by coupling a THz cavity to a doubly-resonant, dual-polarization near-infrared (e.g. telecom band) photonic-crystal nanobeam cavity, allowing the mixing of three mutually orthogonal fundamental cavity modes through a chi(2) nonlinearity. We demonstrate through coupled-mode theory that complete depletion of the pump frequency - i.e., quantum-limited conversion - is possible in an experimentally feasible geometry, with the operating output power at the point of optimal total conversion efficiency adjustable by varying the mode quality (Q) factors.

We develop a theoretical framework for second-order nonlinear difference frequency generation in triply resonant wavelength-scale cavities, demonstrating stable CW conversion with quantum-limited efficiency. We propose a scheme for efficient THz generation based on this framework.

By using a theoretical formalism able to work in both real and k-spaces, the physical origin of the phenomenon of extraordinary transmission of light through quasi-periodic arrays of holes is revealed. Long-range order present in a quasiperiodic array selects the wavevector(s) of the surface electromagnetic mode(s) that allows an efficient transmission of light through subwavelength holes., 4 pages, 4 figures

The theoretical fundamentals of the so called zero velocity Mössbauer spectroscopy is presented to measure the nuclear resonance thickness at zero velocity and total area for nuclear resonance absorption of a given sample in the transmission mode. The methodology to take and analyze the experimental data is presented, including instrumental parameters and the uncertainty in the results, using triangular and sinusoidal signals., Se presenta la base teórica que sustenta la denominada espectroscopia Mössbauer de velocidad cero para medir el espesor resonante nuclear a velocidad cero y el área total para absorción resonante nuclear de una muestra dada en la modalidad de transmisión. Se presenta la metodología para tomar y analizar los datos experimentales, incluyendo parámetros instrumentales y la incertidumbre en los resultados, utilizando señales de forma triangular y sinusoidal.

4 pages, 4 figures.-- et al., The extraordinary optical transmission through periodic arrays of subwavelength holes has been studied extensively since it was first reported in 1998, owing to both its fundamental implications and its technological potential. The picture of the underlying mechanism that emerges from most of the theoretical studies is a resonant process assisted by surface electromagnetic modes, such as surface plasmons. However, these studies consider an infinite array of holes. By combining experiment and theory, we have analysed the influence of the inherent finite size of the arrays and report here the unexpected spatial distribution of light as it emerges from the arrays. This distribution is strongly anisotropic and extremely sensitive to the angle of incidence of the impinging light. The behaviour can be explained by a model that takes into account the asymmetry induced by the array edges, and the effects this has on the emission pattern across the array., Financial support by the EC under Project Nos. FP6-NMP4-CT-2003-505699 (Surface Plasmon Photonics) and FP6-2002-IST-1-507879 (Plasmo-Nano-Devices) is gratefully acknowledged.

In this work, we study how extraordinary electromagnetic transmission through an array of holes in a metallic film appears as a function of the number of holes and their distribution. In order to do that, we have used a theoretical formalism able to analyze the optical properties of finite collections of apertures placed at arbitrary positions in a metallic film. First, we analyze how the total transmission in a hexagonal 2D hole array evolves as the number of holes in the array is increased. Secondly, we study what is the minimal system showing extraordinary electromagnetic transmission. We find numerically that a linear chain of holes can be considered as the basic entity with extraordinary transmission properties.

Lattice surface plasmons enable large-area unidirectional emission of coherent light generated at deep subwavelength scales.

In this work we explore the transmission properties of a single slit in a metallic screen. We analyze the dependence of these properties on both slit width and angle of incident radiation. We study in detail the crossover between the subwavelength regime and the geometrical-optics limit. In the subwavelength regime, resonant transmission linked to the excitation of waveguide resonances is analyzed. Linewidth of these resonances and their associated electric field intensities are controlled by just the width of the slit. More complex transmission spectra appear when the wavelength of light is comparable to the slit width. Rapid oscillations associated to the emergence of different propagating modes inside the slit are the main features appearing in this regime., Comment: Accepted for publication in Phys. Rev. E

In this Letter we introduce a novel route for achieving negative-group-velocity waveguiding at deep-subwavelength scales. Our scheme is based on the strong electromagnetic coupling between two conformal surface plasmon structures. Using symmetry arguments and detailed numerical simulations, we show that the coupled system can be geometrically tailored to yield negative-index dispersion. A high degree of subwavelength modal confinement, of λ/10 in the transversal dimensions, is also demonstrated. These results can assist in the development of ultrathin surface circuitry for the low-frequency region (microwave and terahertz regimes) of the electromagnetic spectrum.

Diffusive random lasers, whose mechanism has been elusive, are now explained by a general theory that encompasses conventional lasers.

We investigate laser emission from optically-pumped rotationally excited molecular gases confined in a metallic cavity. To this end, we have developed a theoretical framework able to accurately describe, both in the spatial and temporal domains, the molecular collisional and diffusion processes characterizing the operation of this class of lasers. The effect on the main lasing features of the spatial variation of the electric field intensity and the ohmic losses associated to each cavity mode are also included in our analysis. Our simulations show that, for the exemplary case of methyl fluoride gas confined in a cylindrical copper cavity, the region of maximum population inversion is located near the cavity walls. Based on this fact, our calculations show that the lowest lasing threshold intensity corresponds to the cavity mode that, while maximizing the spatial overlap between the corresponding population inversion and electric-field intensity distributions, simultaneously minimizes the absorption losses occurring at the cavity walls. The dependence of the lasing threshold intensity on both the gas pressure and the cavity radius is also analyzed and compared with experiment. We find that as the cavity size is varied, the interplay between the overall gain of the system and the corresponding ohmic losses allows for the existence of an optimal cavity radius which minimizes the intensity threshold for a large range of gas pressures. The theoretical analysis presented in this work expands the current understanding of lasing action in optically-pumped far-infrared lasers and, thus, could contribute to the development of a new class of compact far-infrared and terahertz sources able to operate efficiently at room temperature.

We present a comprehensive study of second-order nonlinear difference frequency generation in triply resonant cavities using a theoretical framework based on coupled-mode theory. We show that optimal quantum-limited conversion efficiency can be achieved at any pump power when the powers at the pump and idler frequencies satisfy a critical relationship. We demonstrate the existence of a broad parameter range in which all triply-resonant DFG processes exhibit monostable conversion. We also demonstrate the existence of a geometry-dependent bistable region., Comment: 10 pages, 3 figures

A complete landscape is presented of the electromagnetic coupling between square holes forming a two-dimensional periodic array in a metallic film. By combining both experimental and theoretical results along with a first-principles Fano model, we study the crossover between the physics of metallic wire meshes (when holes occupy most of the unit cell) and the phenomenon of extraordinary optical transmission, which appears when the size of the holes is very small in comparison with the period of the array.

Systematic differences in the UBVRI photometry of SN 1987A exist between the published photometry from CTIO and SAAO. The largest differences occur in the I band where the SAAO photometry is up to 0.4 magnitude brighter than the CTIO photometry. We have measured the filter/phototube response of the CTIO system and have synthesized VRI photometry from the CCD spectrophotometry of SN 1987A obtained at CTIO. The differences between the synthesized and photoelectric photometry for both the CTIO and SAAO natural systems are less than 0.05 magnitude. This confirms our previous suggestion that the nonstellar nature of the supernova spectrum can give rise to large systematic errors in photometry obtained at different sites. The comparison of the light curves of any two supernovae can be in error by a similar amount due to the different natural photometric systems.

An analysis of the optical response of a triangular-shaped photonic band-gap prism is presented. Numerical simulations have been performed in the framework of multiple-scattering theory, which is applied considering spot illumination to avoid diffraction effects. First of all, refractive properties in the frequency range below the first TM band-gap are analyzed and compared with the available experimental data. It validates the approach employed and supports the predictions obtained in the frequency range above the gap. At these high frequencies we found an unusual superprism effect characterized by an angle- and frequency-sensitivity of the intensity of outgoing beams. We report several representative examples that could be used in device applications. The results are interpreted in terms of the corresponding semi-infinite photonic crystal, through the analysis of the coupling between external radiation and bulk eigenmodes, using the 2D Layer- Korringa-Kohn-Rostoker method. The procedure presented here constitutes a simple but functional alternative to the methods used until now with the same purpose., Comment: RevTeX 4, 17 preprint pages, 13 figures, accepted for publication in Phys. Rev. B

We present a theoretical analysis of lasing action in photonic crystal surface-emitting lasers (PCSELs). The semiclassical laser equations for such structures are simulated with three different theoretical techniques: exact finite-difference time-domain calculations, an steady-state ab-initio laser theory and a semi-analytical coupled-mode formalism. Our simulations show that, for an exemplary four-level gain model, the excitation of dark Fano resonances featuring arbitrarily large quality factors can lead to a significant reduction of the lasing threshold of PCSELs with respect to conventional vertical-cavity surface-emitting lasers. Our calculations also suggest that at the onset of lasing action, most of the laser power generated by finite-size PCSELs is emitted in the photonic crystal plane rather than the vertical direction. In addition to their fundamental interest, these findings may affect further engineering of active devices based on photonic crystal slabs. Published version