Europhys. Lett.
Volume 73, Number 2, January 2006
Page(s) 313 - 319
Section Geophysics, astronomy, and astrophysics
Published online 14 December 2005
Europhys. Lett., 73 (2), pp. 313-319 (2006)
DOI: 10.1209/epl/i2005-10385-6

Calculation of the torque exerted by light fields on silver elliptical nanocylinders

C. Rockstuhl and J. Tominaga

National Institute of Advanced Industrial Science and Technology Center for Applied Near-Field Optics Research, Tsukuba Central 4.9 1-1-1 Higashi, Tsukuba, 305-8562, Japan

received 17 June 2005; accepted in final form 23 November 2005
published online 14 December 2005

Diffraction theory is applied to analyze the torque exerted by a Gaussian wave-field on elliptically shaped silver nanocylinders with a size of approximately $20\un{nm}$ in the spectral domain between $300\un{nm}$ and $450\un{nm}$. For that purpose the Multiple Multipole Method is employed to calculate the field distribution across the surface of the particle rigorously and the torque is subsequently determined by employing Maxwell's stress tensor. The particles support as a function of the axis ratio two distinguishable plasmon resonances. It is shown that the particles align with the major axis perpendicular to the optical axis for illumination wavelengths smaller than the plasmon wavelength that is associated with the major axis. For larger illumination wavelengths a flip appears due to a change in the sign of the polarizability and the particles align in the opposite direction, with the major axis parallel to the optical.

94.20.Rr - Interactions between waves and particles.
78.67.Bf - Nanocrystals and nanoparticles.
73.20.Mf - Collective excitations (including excitons, polarons, plasmons and other charge-density excitations).

© EDP Sciences 2006