Hiroo UKITA^*, Takashi SAITOH^† and Noboru SAKAHARA^‡

Faculty of Science and Engineering, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8677, Japan

(Received June 5, 2006; Accepted September 7, 2006)

Optical trapping forces of polystyrene microspheres are analyzed both theoretically and experimentally, and comparisons are made between the two. Discrepancies are mainly caused by straight-ray approximation for axial trapping, and by trapping-position vertical displacement due to gravity for transverse trapping.

Key words: optical tweezers, optical trapping force, trapping position, microsphere, straight ray, parabolic ray, beam waist, axial trapping, transverse trapping

^*E-mail address: ukita@se.ritsumei.ac.jp
^†Currently with NEC, Kawasaki 210-0012, Japan.
^‡Currently with NEC, Kashiwa, Chiba 277-0841, Japan.