We present our investigation of the torque exerted on dielectric elliptical cylinders by highly focused laser beams. The calculations are performed with rigorous diffraction theory, and the size-dependent torque is analyzed as a function of the axis ratio. It is found that highly elongated particles will experience a reversal of the torque for a radius that is approximately one third of the wavelength. This effect is attributed to interference effects inside the structure due to multiple reflections of the incoming wave. The evolution from a perfectly sinusoidal angular dependence of the torque to a more complicated pattern for increasing particle size is presented in detail.
© 2005 Optical Society of America
Carsten Rockstuhl and Hans Peter Herzig, "Calculation of the torque on dielectric elliptical cylinders," J. Opt. Soc. Am. A 22, 109-116 (2005)