Non-Conservative Effects in Optical Trapping of Silicon Nanowires

We measure non-conservative forces in optical trapping of ultra-thin Silicon nanowires by photonic force and torque microscopy. We reveal how the extreme non-spherical shape generates a transverse component of the radiation pressure that result in a thermally activated non-conservative rotation of the nanowire about the trap axis. We explore the behavior with trapping power and scaling with nanowire length. This has implications for optical force calibration and optomechanics with levitated non-spherical particles.