Optical Force on a Metal Nanorod Exerted by a Photonic Jet (original) (raw)
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Optical forces on metallic nanoparticles induced by a photonic nanojet
Optics Express, 2008
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.
Journal of Optics A: Pure and Applied Optics, 2004
Illumination of nano-and micro-particles with a highly focused laser beam will exert a force on them that depends on different parameters, such as the particle size, refractive index and beam waist. In this paper rigorous diffraction theories are used to calculate the force on elliptically shaped dielectric cylinders in three different size regimes. We analyse the conditions for which the particles are attracted or repelled from the optical axis as a function of the geometry. Such a shape dependent response to optical wave-fields could be used to sort particles.
Optical forces in nanorod metamaterial
Scientific reports, 2015
Optomechanical manipulation of micro and nano-scale objects with laser beams finds use in a large span of multidisciplinary applications. Auxiliary nanostructuring could substantially improve performances of classical optical tweezers by means of spatial localization of objects and intensity required for trapping. Here we investigate a three-dimensional nanorod metamaterial platform, serving as an auxiliary tool for the optical manipulation, able to support and control near-field interactions and generate both steep and flat optical potential profiles. It was shown that the 'topological transition' from the elliptic to hyperbolic dispersion regime of the metamaterial, usually having a significant impact on various light-matter interaction processes, does not strongly affect the distribution of optical forces in the metamaterial. This effect is explained by the predominant near-fields contributions of the nanostructure to optomechanical interactions. Semi-analytical model, ap...
Journal of the Optical Society of America A, 2005
The detailed optics of photonic nanojets generated by normal plane-wave incidence on dielectric cylinders is discussed. These nanojets have a subwavelength beam waist and propagate with little divergence for several wavelengths. A physical explanation for this peculiar behavior is presented. Characteristic dimensions of the nanojets for a large range of physical parameters are calculated.
Optical Forces in Plasmonic Nanoparticle Dimers †
The Journal of Physical Chemistry C, 2010
We present calculations of the optical forces between two metal nanospheres forming a hybridized plasmonic dimer. We consider homo-and heterodimers and investigate different plane wave illumination configurations. The forces between the particles are calculated using full Mie theory combined with the Maxwell stress tensor (MST) formalism, as well as by approximate methods, such as the Lorentz force (LF) approach taken in the dipole limit and calculations based on an optical potential. We show that the simplified calculation schemes can lead to serious errors in the case of strongly interacting particles and low damping. In particular, we find that equilibrium configurations, corresponding to vanishing optical forces, only are possible for homodimers illuminated in the end-fire configuration and for heterodimers, although multipolar effects and damping radically reduce the repulsive interactions in the latter case.
Optical forces on microparticles in an evanescent laser field
Optics Letters, 1999
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 ref lection in a f lat substrate. The inf luence 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 f lat 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.
Optical Gradient Forces of Strongly Localized Fields
PHYSICAL REVIEW LETTERS, 1998
We present a new approach for determining optical gradient forces applied by strongly focused laser beams on dielectric particles. We show that when the electromagnetic field is focused to a diffraction limited spot a dipole approximation is valid for any particle size. We derive intuitive predictions for force-displacement curves, maximal trapping forces, and force constants. The theory fits well with recent measurements of particles trapped by laser tweezers. We also discuss effects of radiation pressure and gravity. [S0031-9007(98)06883-5] 05.40. + j, 42.25.Fx The technique of optical tweezers has opened new experimental horizons in the biophysical and colloidal realm. Since the pioneering work of Ashkin [1-3], who first introduced the use of optical gradient forces, researchers have found diverse applications of trapping and manipulating single particles such as dielectric spheres and cellular organelles. Recent work with laser tweezers has allowed quantitative measurements of piconewton forces and nanometer displacements such as those produced by the action of single molecular motors. In addition, laser tweezers are widely used to measure mechanical elastic properties of cellular components such as DNA strands, molecular filaments, and membranes [4-6]. These experimental advances require an understanding and determination of optical gradient forces in a predictive and tractable manner. Theoretical calculations to date that predict the force acting on a general particle are strictly applicable to either small particles (electromagnetic theory) or very large particles (ray optics calculations) . In the intermediate regime (typically 1 10 mm), which is often the most interesting one, both theories are incompatible with experimental results .
Ray-optics model for optical force and torque on a spherical metal-coated Janus microparticle
Photonics Research, 2015
In this paper, we develop a theoretical method based on ray optics to calculate the optical force and torque on a metallo-dielectric Janus particle in an optical trap made from a tightly focused Gaussian beam. The Janus particle is a 2.8 μm diameter polystyrene sphere half-coated with gold thin film several nanometers in thickness. The calculation result shows that the focused beam will push the Janus particle away from the center of the trap, and the equilibrium position of the Janus particle, where the optical force and torque are both zero, is located in a circular orbit surrounding the laser beam axis. The theoretical results are in good agreement qualitatively and quantitatively with our experimental observation. As the ray-optics model is simple in principle, user friendly in formalism, and cost effective in terms of computation resources and time compared with other usual rigorous electromagnetics approaches, the developed theoretical method can become an invaluable tool for understanding and designing ways to control the mechanical motion of complicated microscopic particles in various optical tweezers.