NON CONSERVATIVE OPTICAL FORCES FOR SILICON NANOWIRES IN OPTICAL TRAPS A. MAGAZZU1,2,*, A. IRRERA1, P. ARTONI3, S. H. SIMPSON4, S. HANNA4, P. H. JONES5, F. PRIOLO3, P. G. GUCCIARDI1, and O. M. MARAGÓ1,* 1 CNR-IPCF, Istituto per i Processi Chimico-Fisici, Messina, Italy 2 Dottorato in Fisica, Università di Messina , Messina, Italy 3 Matis CNR-IMM and Dipartimento di Fisica, Università di Catania, Catania, Italy 4 H. H. Wills Physics Laboratory, University of Bristol, Bristol, UK 5 Department of Physics and Astronomy, University College London, London, UK *Corresponding authors:
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[email protected] Abstract For a non-spherical particle the non-conservative forces We measure non-conservative forces in optical can be considered composed by two contributions. A first trapping of ultra-thin Silicon nanowires by photonic force contribution depends on the standard non-homogeneous and torque microscopy. We reveal how the extreme non- radiation pressure due to the gaussian geometry of the spherical shape generates a transverse component of the laser beam that may yield a rotational force in ρ-z plane radiation pressure that results in a thermally activated even for a spherical trapped particle [4,5]. The second non-conservative rotation of the nanowire about the trap contribution, manifest for nonspherical objects, depends axis. We explore the behavior with trapping power and on alignment along the axial direction, that generates a scaling with nanowire length. This has implications for transverse force (optical lift effect) [6] that causes rotations optical force calibration and optomechanics with levitated and precessions in the ρ-z plane.