Optical forces on metallic nanoparticles induced by a photonic nanojet

Faculty of Engineering, General and Theoretical Electrical Engineering (ATE), University of Duisburg-Essen, D-47057 Duisburg, Germany.
Optics Express (Impact Factor: 3.49). 10/2008; 16(18):13560-8. DOI: 10.1364/OE.16.013560
Source: PubMed


We investigate the optical forces acting on a metallic nanoparticle when the nanoparticle is introduced within a photonic nanojet (PNJ). Optical forces at resonance and off-resonance conditions of the microcylinder or nanoparticle are investigated. Under proper polarization conditions, the whispering gallery mode can be excited in the microcylinder, even at off resonance provided that scattering from the nanoparticle is strong enough. The optical forces are enhanced at resonance either of the single microcylinder or of the nanoparticle with respect to the forces under off-resonant illuminations. We found that the optical forces acting on the nanoparticle depend strongly on the dielectric permittivity of the nanoparticle, as well as on the intensity and the beam width of the PNJ. Hence, metallic sub-wavelength nanoparticle can be efficiently trapped by PNJs. Furthermore, the PNJ's attractive force can be simply changed to a repulsive force by varying the polarization of the incident beam. The changed sign of the force is related to the particle's polarizability and the excitation of localized surface plasmons in the nanoparticle.

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    • "The interest on PNJ, and optical tweezers (OT) is that combined they can contributed significantly to applications such as nanoscale processing [10, 11, 12, 13], high-resolution microscopy [3, 14], and enhanced elastic spectroscopy, such as Raman [15, 16] and fluorescence [17], or inelastic enhancement by backscattering from nanoparticles [18]. Up to this moment the only studies regarding optical forces and PNJs, are related to the radiation pressure effect that the PNJ produces on a nanoparticle [19] [20] [21]. In contrast, the scope here is different, we would investigate the optical force on a microsphere that results in a PNJ. "
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    ABSTRACT: Photonic nanojets have been brought into attention ten years ago for potential application in ultramicroscopy, because of its sub-wavelength resolution that can enhance detection and interaction with matter. For these novel applications under development, the optical trapping of a sphere acts as an ideal framework to employ photonic nanojets. In the present study, we generated nanojets by using a highly focused incident beam, in contrast to traditional plane waves. The method inherits the advantage of optical trapping, especially for intracellular applications, with the microsphere in equilibrium on the beam propagation axis and positioned arbitrarily in space. Moreover, owing to optical scattering forces, when the sphere is in equilibrium, its center shifts with respect to the focal point of the incident beam. However, when the system is in stable equilibrium with a configuration involving optical tweezers, photonic nanojets cannot be formed. To overcome this issue, we employed double optical tweezers in an unorthodox configuration involving two collinear and co-propagating beams, the precise positioning of which would turn on/off the photonic nanojets, thereby improving the applicability of photonic nanojets.
    Journal of Quantitative Spectroscopy and Radiative Transfer 02/2015; 162:122. DOI:10.1016/j.jqsrt.2015.03.019 · 2.65 Impact Factor
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    • "We can now write the ensemble-averaged force as a sum of coherent modes by using its expression from the momentum conservation law in terms of the Maxwell stress tensor (MST) [44] [45] [46]: "
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    ABSTRACT: We present a theory and computation method of radiation pressure from partially coherent light by establishing a coherent mode representation of the radiation forces. This is illustrated with the near field emitted from a Gaussian Schell model source, mechanically acting on a single cylinder with magnetodielectric behavior, or on a photonic molecule constituted by a pair of such cylinders. Thus after studying the force produced by a single particle, we address the effects of the spatial coherence on the bonding and antibonding states of two particles. The coherence length manifests the critical limitation of the contribution of evanescent modes to the scattered fields, and hence to the nature and strength of the electromagnetic forces, even when electric and/or magnetic partial wave resonances are excited.
    Journal of the Optical Society of America A 02/2014; 31(1):206-16. DOI:10.1364/JOSAA.31.000206 · 1.56 Impact Factor
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    • "This fact attracts a particular interest to the PJ phenomenon and benefits in wide practical applications, e.g., in designing the ultrahigh-resolution (nanometer-scale) optical sensors [3]. Besides, the PJ is used as surgical optical scalpel [4], optical tool for nano-object manipulation [5], element in optical data storage with ultrahigh resolution [6], and in the technology of nano-photolithography [7]. A rather thorough review of works devoted to theoretical and experimental investigations of the PJ phenomenon can be found in the recent paper [8]. "
    Dataset: JQSRT final

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