Terahertz plasmonic laser radiating in an ultra-narrow beam

Plasmonic lasers (spasers) generate coherent surface-plasmon-polaritons (SPPs) and could be realized at subwavelength dimensions in metallic cavities for applications in nanoscale optics. Plasmonic cavities are also utilized for terahertz quantum-cascade lasers (QCLs), which are the brightest available solid-state sources of terahertz radiation. A long standing challenge for spasers is their poor coupling to the far-field radiation. Unlike conventional lasers that could produce directional beams, spasers have highly divergent radiation patterns due to their subwavelength apertures. Here, we theoretically and experimentally demonstrate a new technique for implementing distributed-feedback (DFB) that is distinct from any other previously utilized DFB schemes for semiconductor lasers. The so-termed antenna-feedback scheme leads to single-mode operation in plasmonic lasers, couples the resonant SPP mode to a highly directional far-field radiation pattern, and integrates hybrid SPPs in surrounding medium into the operation of the DFB lasers. Experimentally, the antenna-feedback method, which does not require the phase matching to a well-defined effective index, is implemented for terahertz QCLs, and single-mode terahertz QCLs with beam divergence as small as 4 x 4 degree are demonstrated, which is the narrowest beam reported for any terahertz QCL to-date. Moreover, in contrast to negligible radiative-field in conventional photonic band-edge lasers, in which the periodicity follows the integer multiple of half-wavelength inside active medium, antenna-feedback breaks this integer-limit for the first time and enhances the radiative-field of lasing mode. The antenna-feedback scheme is generally applicable to any plasmonic laser with a Fabry-Perot cavity irrespective of its operating wavelength, and could bring plasmonic lasers closer to practical applications

Teorizando las Relaciones Internacionales y el ascenso de China: una investigación preliminar

This paper critically analyses the case study of Chinese international relations theory through the lens of a non-Western International relations theoretical framework.There should be an attempt to democratise the existing international relations discipline because societal interactions among the countries across the globe cannot be judged by the yardstick of Western experiences. Non-Western international relations theories can be also generated under the post-positivist methodological framework, as it is equally important to include the localised voices and experiences of Asian, African and Latin American countries by reactivating their local historical traditions and ancient philosophies, sociological perspective and ontological, epistemological and axiological dimension of international relations theories 3. Key words: International Relations Theory - Tribute System – Confucian Model of Governance – World OrderEste artículo analiza críticamente la teoría china de las relaciones internacionales, como estudio de caso, desde la perspectiva del marco teórico de las relaciones internacionales no occidentales. Debe haber un intento de democratizar la disciplina existente de las relaciones internacionales ya que las interacciones sociales entre los países del globo no pueden ser juzgadas desde la perspectiva de las experiencias occidentales. Las teorías de las relaciones internacionales no occidentales también pueden ser generadas dentro del marco metodológico post-positivista ya que es igualmente importante incluir las voces y experiencias localizadas de los países asiáticos, africanos y latinoamericanos a partir de la reactivación de sus tradiciones históricas locales y sus filosofías antiguas, la perspectiva sociológica y la dimensión ontológica, epistemológica y axiológica de las teorías de las relaciones internacionales. Palabras Claves: Teoría de las Relaciones Internacionales - Sistema de tributo – modelo confuciano de gobernanza – orden mundi

Online Algorithms with Discrete Visibility - Exploring Unknown Polygonal Environments

The context of this work is the exploration of unknown polygonal environments with obstacles. Both the outer boundary and the boundaries of obstacles are piecewise linear. The boundaries can be nonconvex. The exploration problem can be motivated by the following application. Imagine that a robot has to explore the interior of a collapsed building, which has crumbled due to an earthquake, to search for human survivors. It is clearly impossible to have a knowledge of the building's interior geometry prior to the exploration. Thus, the robot must be able to see, with its onboard vision sensors, all points in the building's interior while following its exploration path. In this way, no potential survivors will be missed by the exploring robot. The exploratory path must clearly reflect the topology of the free space, and, therefore, such exploratory paths can be used to guide future robot excursions (such as would arise in our example from a rescue operation)