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8 págs.; 8 figs.; 1 tab. ; PACS number s : 73.20.Mf, 78.68. m, 65.40. b, 41.20.Jb ; We present a theoretical framework that allows us to investigate the scattering of terahertz surface plasmon polaritons (SPP's) by arrays of subwavelength grooves and ridges on semiconductors. The formulation is based on the reduced Rayleigh equation resulting upon imposing an impedance boundary condition. Guided by approximate estimations of the broadening with temperature of the first gap in the SPP dispersion relation in the case of indium antimonide samples with rectangular grooves, numerical calculations are carried out to determine the spectral dependence of all the SPP scattering channels (reflection, transmission, and radiation) in the immediate vicinity of that gap. The thermally induced switching of the SPP reflection and transmission nearby the lower SPP band edge is investigated as a function of groove parameters (size and number); near-field intensity maps are also presented. We thus shed light on the SPP scattering and switching physical mechanisms, thereby providing the most suitable experimental configurations. © 2006 The American Physical Society. ; This work was supported in part by the Spanish "Ministerio de Educación y Ciencia" Grant Nos. BFM2003-0427 and FIS2004-0108 and "Comunidad de Madrid" Grant MICROSERES and by the European Union Grant HPRN-CT- 2002-00206. The work of J.G.R. was supported by the "Stichting voor Fundamenteel Onderzoek der Materie" FOM, which is financially supported by the "Nederlandse Organisatie voor Wetenschappelijk Onderzoek" NWO. ; Peer Reviewed

6 págs.; 6 figs. ; PACS number s : 73.20.Mf, 42.79.Dj, 42.25.Bs, 78.68. m ; Using terahertz time-domain spectroscopy measurements, we demonstrate optical switching of the transmission of terahertz surface plasmon polaritons (SPPs) propagating on an indium antimonide surface through Bragg scattering on grooves. The switching of the in-plane transmission of SPPs through the grooves is mediated by the modification of the stop-gap width due to changes of the surface plasmon characteristics, which are induced by the optical generation of charge carriers. The use of a semiconductor surface allows us to achieve switching at extremely low excitation powers. The experimental data can be quantitatively reproduced using rigorous numerical calculations for surfaces with varying dielectric function. Such an optically active device opens further possibilities for low-frequency surface plasmon optics. © 2006 The American Physical Society. ; Financial support from the European Union through the projects Interaction Grant No. HPRN-CT-2002-00206 and Metamorphose Grant No. NMP3-CT-2004-500252, and from the Deutsche Forschungsgemeinschaft. The work of J.G.R. was supported in part by the "Stichting voor Fundamenteel Onderzoek der Materie FOM," which is financially supported by the "Nederlandse Organisatie voor Wetenschappelijk Onderzoek NWO." The work of J.A.S.G. was supported in part by the Spanish Comunidad de Madrid Grants No. GR/MAT/0425/ 2004 and MICROSERES and MEC Grants No. FIS2006- 07894 and No. FIS2004-0108. ; Peer Reviewed

6 pags., 4 figs. ; The near-zero forward intensity condition for light scattering by a dielectric dipolar sphere is usually associated with the generalized second Kerker condition, at which equal amplitude electric and magnetic dipolar responses are phase-shifted by π. As we show, this condition does lead to optimal backward light scattering for a given scattering cross section. However, it is clearly insufficient to give rise to the nearly zero optical forward scattering, in striking contrast to the actual view of the problem. In fact, we show that the generalized second Kerker condition leads to an energy radiation pattern that ranges all possible optical scattering diagrams depending on the total scattering cross section. Interestingly, we demonstrate that optimization of backward intensity, near the electric and magnetic dipolar resonances, leads to the counterintuitive result of a far-field energy radiation pattern with nearly zero backscattering. ; This research was supported by the Basque Government (Project PI-2016-1-0041 and PhD Fellowship PRE-2018- 2-0252) and by the Spanish MINECO and MICINN and European Regional Development Fund (ERDF) Projects: FIS2015-69295-C3-2-P, FIS2015-69295-C3-3-P, FIS2017- 91413-EXP, FIS2017-82804-P, PGC2018-095777-B-C21, and PhD Fellowship FPU15/03566.

6 pags., 4 figs. ; Controlling the helicity and directionality of the scattered light by dielectric particles is paramount to a variety of phenomenology of interest in all-dielectric optics and photonics. In this paper, we demonstrate that the helicity of an incoming beam is not preserved when several multipoles contribute to the scattering. This inhibits the usual link between duality restoration and zero optical backscattering condition. In addition, we show that the helicity conservation in the scattering by high-refractive index dielectric Mie spheres can be used as a probe of pure-multipolar spectral regions, particularly of dipolar nature, beyond its presumed spectral interval. This finding reveals that the dipolar behavior is not necessarily limited to small particles, in contrast to the current understanding. Interestingly, our formalism allows us to demonstrate that the optimum forward light scattering condition, predicted for a particular nanosphere, is fulfilled for an infinite number of refractive indexes in these dipolar regimes. ; This research was supported by the Basque Government (Project No. PI-2016-1-0041 and Ph.D. fellowship PRE2018-2-0252) and by the Spanish MINECO and MICINN and European Regional Development Fund (ERDF) Projects No. FIS2015-69295-C3-3-P, No. FIS2017-91413-EXP, No. FIS2017-82804-P, and No. PGC2018-095777-B-C21 and Ph.D. fellowship FPU15/03566. X.Z.-P. acknowledges funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant Agreement No. 795838.