A sophisticated modeling program was used recently to predict the trapping and the manipulation properties of elongated cylindrical objects in the focal region of a high-intensity laser beam. On the basis of the model, the cylinders should align their longest diagonal dimension with the propagation axis of the laser beam and follow the beam when it is displaced transverse to the cylinder's central axis. Experimental confirmation of the cylinder's behavior is presented and confirms the suitability of the enhanced ray-optics approach to modeling micrometer-scale objects in optical-trap environments.

An enhanced photon propagation method is used to calculate the forces and torque present on each sphere of a system of particles located in the vicinity of focused laser-trapping beams. Infinitesimal trajectory displacements are computed through classical mechanics and the new particle position used to define the next trapping system geometry considered. Repeated applications of the process, implemented as a computer program, enables full trajectory plotting and the dynamic behavior of the systems to be explored as a function of time.

Long cylindrical objects have been observed to align their central axis with the propagation axis of the illuminating laser beam through the action of radiation-pressure-generated force and torque. A cylindrically shaped microactuator based on this principle and suitable for micromachine applications is examined theoretically. When four in-plane laser beams converging at a common point centered on the cylinder are used, the cylinder can be made to rotate about a pivot point. In one mode, smooth, continuous, and reversible rotation is possible, whereas the other cylinder can be step rotated and locked, similar to the operation of conventional stepping motors. The properties of the device are analyzed based on obtaining either a constant rotation rate with variable beam power levels or a quasi-constant rotation rate with constant beam power levels or on using a fixed beam sequence rate that matches the system parameters and produces smooth or stepped operation.