Tilt angle dependent three-dimensional-position detection of a trapped cylindrical particle in a focused laser beam

We investigated theoretically the applicability of an optically trapped cylindrical particle as a local probe in photonic force microscopy. To do this we calculated the far-field scattering from a subwavelength-sized dielectric cylinder in a highly focused laser field. From this we obtained interferometric three-dimensional-position detection signals and compared these to signals calculated for a spherical particle. We have calculated the accuracy to which the position of an optically trapped cylinder can be determined, as a function of the cylinder’s orientational fluctuations. The position accuracy is better than a few nanometers for tilt angle fluctuations up to several degrees. Our study is relevant for trapping experiments, where the influence of angle fluctuations needs to be estimated.