A theoretical analysis of electromagnetic forces on neutral particles in an hollow waveguide is presented. We show that the effective scattering cross section of a very small (Rayleigh) particle can be strongly modified inside a waveguide. The coupling of the scattered dipolar field with the waveguide modes induce a resonant enhanced backscattering state of the scatterer-guide system close to the onset of new modes. The particle effective cross section can then be as large as the wavelength even far from any transition resonance. As we will show, a small particle can be strongly accelerated along the guide axis while being highly confined in a narrow zone of the cross section of the guide. 42.50.Vk, 32.80.Lg, 42.25.Bs Demonstration of levitation and trapping of micronsized particles by radiation pressure dates back to 1970 and the experiments reported by Ashkin and co-workers [1]. Since then, manipulation and trapping of neutral particles by optical forces has had a revolutionary impact on a variety of fundamental and applied studies in physics, chemistry and biology [2]. These ideas were extended to atoms and molecules where radiation pressure can be very large due to the large effective cross section (of the order of the optical wavelength) at specific resonances [1,3]. When light is tuned close to a particular transition, optical forces involves (quantum) absorption and reradiation by spontaneous emission as well as coherent (classical) scattering of the incoming field with the induced dipole [4]. Selective control of the strong interplay between these two phenomena is the basis of laser cooling and trapping of neutral atoms [5].However, far from resonance, light forces on atoms, molecules and nanometer sized particles are, in general, very small. Here we show that the scattering cross section of a very small (Rayleigh) particle can be strongly modified inside a waveguide. The coupling of the scattered dipolar field with the waveguide modes induce a resonant enhanced backscattering state of the scattererguide system close to the onset of new modes. Just at the resonance, the effective cross section becomes of the order of the wavelength leading to an enhanced resonant radiation pressure which does not involve any photon absorption phenomena. As we will show, a small particle not only can be strongly accelerated along the guide axis but it can also be highly confined in a narrow zone of the cross section of the guide.For the sake of simplicity we consider a twodimensional xz waveguide with perfectly conducting walls and cross section D. The particle is then represented by a cylinder located at r 0 = (x 0 , z 0 ) with its axis along oy and radius much smaller than the wavelength (see top of Fig.1). However, apart from some depolarization effects, the analysis contain the same phenomena as the full three-dimensional problem [6] and hence it permits an understanding of the basic physical processes involved in the optical forces without loss of generality.An s-polarized electromagnetic wave is assumed (the elec...

We present a theory based on an exact calculation of the radiation forces on a microsized particle illuminated by evanescent waves created under total internal reflection in a flat substrate. The influence of the proximity of this interface to the particle is analyzed by a numerical simulation that addresses multiple scattering of light between the particle and the dielectric flat surface. We thus give an interpretation of the experimental results of Kawata and Sugiura [Opt. Lett. 17, 772 (1992)] and put forward a method that is capable of predicting new effects.

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Subject classification: 78.60.Kn; S10.15The thermoluminescent properties of polycrystalline Dy doped strontium tetraborate are reported. Its efficiency is at least five times larger than that of TLD-700 and therefore comparable to that of Cu doped lithium tetraborate. The isometric plot shows two spectral bands at approximately 480 and 580 nm like the emission spectra of Dy doped phosphors reported to date.

We present a method for sizing metallic nanowires through the analysis of the extinction spectra of the scattered light when the wires are illuminated alternatively with p- and s-polarization waves. The method is applied to isolated silver nanowires in air or immersed in index matching oil. The dielectric function of silver is affected by the size of the cylinders, and its influence on the extinction spectra near the plasmon resonance or near the dip position is considered. Due to the size of the nanocylinders, it is necessary to include two different permittivities in the electromagnetic model to analyse the behaviour of the material under different polarization incidences. This introduces anisotropy in the system, which comprises isotropic cylinders. The behaviour of the extinction spectra for p-waves allows us to determine the wire radii, taking into account the plasmon peak position for radii larger than 7 nm, or alternatively, by using the contrast between maximum and minimum intensity near the plasmon frequency, for radii lower than 5 nm. For s-waves, although no plasmon peak appears, we can determine the radii by analysing the contrast between the ridge of the spectra near 260–275 nm and the minimum near 320–330 nm for radii larger than 10 nm, or analysing the slope in the spectra over 350 nm, for radii below 10 nm. The present study shows that spectral extinction is a very simple and inexpensive technique that can be useful for characterizing the radius of nanocylinders when electron microscopy (TEM or SEM) is not available.

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Exact calculations of the near-field electromagnetic force on a nanoparticle exerted by the presence of a corrugated dielectric interface are carried out. The illumination of this system excites the particle eigenmodes. The calculation is two-dimensional, so the nanoparticle is actually a nanocylinder that scans parallel to the interface. This system constitutes a model of force transduction and surface topography imaging for a photonic-force microscope with signal enhancement owing to morphological resonance excitation of the probe.