Fig. 1: Principle of the optical microrobot (OPTOBOT) for out-of-plane rotation.
a Design of the OPTOBOT showing the laser beams positions with their coordinates (Traps 1 to 3) onto it with propagation along the z-direction. Here, Optical Trap 1 and 2 are used to hold the OPTOBOT while the off-axis Trap 3 is used to create pressure on the OPTOBOT's helix and generate its rotation. We depict on the helix the norm of the electric field created by the Gaussian beam illumination via the false color scale on its surface. b The rotation of the OPTOBOT is only possible under a constant sign of the torque along the x-direction, and we depict the normalized τx versus different angles occupied during a full revolution of the OPTOBOT, from 0 to 120 degrees (equivalent to the full rotation due to the C3 rotational symmetry of the structure). Where nm is the refractive index of the medium (water), P is the laser power, r is the radius of the helix part interacting with the laser beam, and c is the light velocity. This calculation is done while assuming the two other traps generate a stable stiffness and do not allow the OPTOBOT to move, and give the only possible motion a revolution along the x-axis. A positive value of τx is observed. In (c) we show the magnitude of Maxwell stress tensor for different angles during the rotation. The color map is shown for each two angles, while the red arrows show the displacement field direction. The calculations were done assuming an input laser power of 630 mW. d The rotation of the robot is illustrated for different angles, the rotation is clockwise as shown by the arrow, and the OPTOBOT returns to the same configuration at angle 120°.
