Optical manipulation of macroscopic curved objects

Laser has become a powerful tool to manipulate micro-particles and atoms by radiation pressure or photophoretic force, but its effectiveness for large objects is less noticeable. Here, we report the direct observation of unusual light-induced attractive forces that allow manipulating centimeter-sized curved absorbing objects by a light beam. This force is attributed to the radiometric effect caused by the curvature of the vane and its magnitude and temporal responses are directly measured with a pendulum. Simulations suggest that the force arises from the bending of the vane, which results in a temperature difference of gas molecules between the concave and convex sides due to unbalanced gas convection. This large force (~4.4 μN) is sufficient to rotate a motor with four curved vanes at speeds up to 600 r/min and even lifting a large vane. Manipulating macroscopic objects by light could have significant applications for solar radiation-powered near-space propulsion systems and for understanding the mechanisms of negative photophoretic forces.