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Optical Forces and Torques Acting on Non-spherical Metallic Nanoparticles

M. Siler[1], O. Brzobohaty[1], V. Karasek[1], P. Zemanek[1]
[1]Inst. Scientific Instruments of the ASCR, Brno, Czech Republic

Metallic nanoparticles (NPs) are nowadays used in various areas of biology, chemistry or physics. Focused laser beams, optical tweezers, may be used to manipulate such NPs. However, experimental studies showed that there is a discrepancy between their predicted and observed behavior. Models assuming the spherical shape of a nanoparticle predict spatial confinement only for particles smaller than 100 nm although larger ones were confined experimentally. Noble metals form variously shaped NPs, e.g. sphere, cube, decahedron or various plates. We show that the shape of nanoparticles is a key parameter that enables their trapping in optical tweezers. Especially larger flat particles tend to reorient themselves perpendicularly to the beam polarization which strongly decreases their scattering and enables the optical trapping.