Antonio Alvaro Ranha Neves

Publications (30) View all

• Source

  Available from: Antonio Alvaro Ranha Neves

  Article: Effect of finite terms on the truncation error of Mie series.

  Antonio Alvaro Ranha Neves, Dario Pisignano
  [show abstract] [hide abstract]
  ABSTRACT: The finite sum of the squares of the Mie coefficients is very useful for addressing problems of classical light scattering. An approximate formula available in the literature, and still in use today, has been developed to determine a priori the number of the most significant terms needed to evaluate the scattering cross section. Here, we obtain an improved formula, which includes the number of terms needed for determining the scattering cross section within a prescribed relative error. This is accomplished using extended precision computation for a wide range of commonly used size parameters and indices of refraction. The revised formula for the finite number of terms can be a promising and valuable approach for efficient modeling light scattering phenomena.
  Optics Letters 06/2012; 37(12):2418-20. · 3.40 Impact Factor
• Source

  Available from: Antonio Alvaro Ranha Neves

  Article: Expansion of Arbitrary Electromagnetic Fields in Terms of Vector Spherical Wave Functions

  W. L. Moreira, A. A. R. Neves, M. K. Garbos, T. G. Euser, P. St. J. Russell, C. L. Cesar
  [show abstract] [hide abstract]
  ABSTRACT: Since 1908, when Mie reported analytical expressions for the fields scattered by a spherical particle upon incidence of an electromagnetic plane-wave, generalizing his analysis to the case of an arbitrary incident wave has proved elusive. This is due to the presence of certain radially-dependent terms in the equation for the beam-shape coefficients of the expansion of the electromagnetic fields in terms of vector spherical wave functions. Here we show for the first time how these terms can be canceled out, allowing analytical expressions for the beam shape coefficients to be found for a completely arbitrary incident field. We give several examples of how this new method, which is well suited to numerical calculation, can be used. Analytical expressions are found for Bessel beams and the modes of rectangular and cylindrical metallic waveguides. The results are highly relevant for speeding up calculation of the radiation forces acting on small spherical particles placed in an arbitrary electromagnetic field, for example in optical tweezers.
  03/2010;
• Source

  Available from: Antonio Alvaro Ranha Neves

  Article: Electromagnetic forces for an arbitrary optical trapping of a spherical dielectric

  Antonio Alvaro Ranha Neves, Adriana Fontes, Liliana de Ysasa Pozzo, Andre Alexandre de Thomaz, Enver Chillce, Eugenio Rodriguez, Luiz Carlos Barbosa, Carlos Lenz Cesar
  [show abstract] [hide abstract]
  ABSTRACT: Analytical solution for optical trapping force on a spherical dielectric particle for an arbitrary positioned focused beam is presented in a generalized Lorenz-Mie and vectorial diffraction theory. In this case the exact electromagnetic field is considered in the focal region. A double tweezers setup was employed to perform ultra sensitive force spectroscopy and observe the forces, demonstrating the selectively couple of the transverse electric (TE), transverse magnetic (TM) modes by means of the beam polarization and positioning, and to observe correspondent morphology-dependent resonances (MDR) as a change in the optical force. The theoretical prediction of the theory agrees well with the experimental results. The algorithm presented here can be easily extended to other beam geometries and scattering particles.
  11/2006;
• Source

  Available from: Antonio Alvaro Ranha Neves

  Article: Multi-photon in situ synthesis and patterning of polymer-embedded nanocrystals

  Andrea Camposeo, Marco Polo, Antonio A. R. Neves, Despina Fragouli, Luana Persano, Sandra Molle, Anna M. Laera, Emanuela Piscopiello, Vincenzo Resta, Athanassia Athanassiou, Roberto Cingolani, Leander Tapfer, Dario Pisignano
  [show abstract] [hide abstract]
  ABSTRACT: The in-situ synthesis and patterning of CdS nanocrystals in a polymer matrix is performed via multi-photon absorption. Quantum-sized CdS nanocrystals are obtained by irradiating a Cadmium thiolate precursor dispersed in a transparent polymer matrix with a focused near infrared femtosecond laser beam. High resolution transmission electron microscopy evidences the formation of nanocrystals with wurtzite crystalline phase. Fluorescent, nanocomposite patterns with sub-micron spatial resolution are fabricated by scanning the laser beam on the polymer/precursor composite. Moreover, the emission energy of the CdS nanocrystals can be tuned in the range 2.5-2.7 eV, by changing the laser fluences in the range 0.10-0.45 J cm-2. This method enables therefore the synthesis of luminescent, CdS-based composites to be used within patterned nanophotonic and light-emitting devices.
  Journal of Materials Chemistry 04/2012; · 5.97 Impact Factor
• Source

  Available from: Antonio Alvaro Ranha Neves

  Article: Laser emission from electrospun polymer nanofibers.

  Andrea Camposeo, Francesca Di Benedetto, Ripalta Stabile, Antonio A R Neves, Roberto Cingolani, Dario Pisignano
  Small 03/2009; 5(5):562-6. · 8.35 Impact Factor