Rotation of Optically Trapped Particles in Air

Abstract

We have demonstrated optically induced rotation of microscopic dielectric particles in air. The particles were anisotropically shaped, and were simultaneously trapped three-dimensionally and rotated about the beam axis, which depended solely on the radiation pressure of an extremely focused laser light. It was observed that the rotational speed was linearly dependent on the irradiated beam power and the slope of the fitting lines revealed up to 860 rpm/mW for 3.0 µm-diameter-particles and 540 rpm/mW for 4.0 µm-diameter-particles, which was much higher than the previously reported values measured in water. This technique will be useful for micromotors and microfans assembled in microelectromechanical systems.

Cell manipulation by use of diamond microparticles as handles of optical tweezers

“…However, with irregularly shaped objects, the net torque will not necessarily be zero when the net force is balanced. 19,20 This result is different from that for a spherically shaped object for which the net torque that results from a Gaussian-shaped trapping force is zero because of cancellation by geometric symmetry. In a viscous medium, this net torque will be balanced by the drag torque, ϭ D⍀, where D is the drag coefficient and ⍀ is the angular speed.…”

“…With a constant D, the angular speed could thus be found to be linearly proportional to the applied optical intensity, which is also proportional to the net torque. Self-rotation was previously achieved for irregularly shaped nonbirefringent particles with a laser beam that had a fundamental Gaussian mode and a fixed linear polarization, 19,20 even in a three-dimensional trap in air. 20 In our experiments, the rotation speeds and directions of the diamond microparticles were affected by particle shape, so they are different for different particles with a fixed laser power.…”

“…Self-rotation was previously achieved for irregularly shaped nonbirefringent particles with a laser beam that had a fundamental Gaussian mode and a fixed linear polarization, 19,20 even in a three-dimensional trap in air. 20 In our experiments, the rotation speeds and directions of the diamond microparticles were affected by particle shape, so they are different for different particles with a fixed laser power. As in previous experiments, 19,20 the rotation speed of a single diamond particle was linearly dependent on the illuminated laser power.…”

“…Recently there were several reports of selfrotation of irregularly shaped particles in a laser trap with a fixed linearly polarized light. 19,20 The selfrotation was caused by the torque that resulted from the total forces' acting on the particle surface. The rotation speed was found to be linearly dependent on the irradiated beam power.…”

Optical Binding in Air

“…Optical trapping in air and vacuum remains a difficult task due to Van der Waals forces several orders of magnitude larger than optical forces. In the literature, two possibilities were explored: the use of aerosols [1][2][3][4] and mechanical vibration coupled with strongly focused cw laser beams [5,16,7,8]. Afterwards, self-assembled structures of microparticles under strong laser illumination have been demonstrated [9][10][11][12].…”