Influences of the Inserted Angle of an Optical Fiber for an Optical Trapping
Biological cell could be trapped by a single laser beam from an optical fiber end inserted at an angle to a sample chamber. We have already developed an optical trapping system. A temperature stabilized 1480nm cw diode laser was used as the light source. The fiber end had a hemispherical micro-lens with 5μm radius of curvature for focusing the laser beam. These trapping fibers were inserted into a sample cell at an angle. The microsphere, 10μm diameter particle (refractive index 1.4), could be trapped. We theoretically analyzed the optical forces exerted on a microsphere by laser beams. The optical force on a microsphere divides itself into two components, the force in the beam axial direction of the light and a transverse force. The transverse optical force acted to pull the sphere back. We investigated the relation between the pulling force and the inserted angle of an optical fiber into a sample chamber. The microsphere is trapped at the point where the horizontal directed optical forces are balanced. We theoretically verified that the inserted angle of an optical fiber into a sample chamber was important parameter. It was found that a small inserted angle produced a weak pulling force.
Tojiro Aoyama, Hideki Aoyama, Atsushi Matsubara, Hayato Yoshioka and Libo Zhou
N. Watanabe and K. Taguchi, "Influences of the Inserted Angle of an Optical Fiber for an Optical Trapping", Key Engineering Materials, Vols. 523-524, pp. 1053-1058, 2012