Optical Review

, Volume 15, Issue 2, pp 97–104

Rotation rate of a three-wing rotor illuminated by upward-directed focused beam in optical tweezers

Regular Papers

DOI: 10.1007/s10043-008-0014-z

Cite this article as:
Ukita, H., Ohnishi, T. & Nonohara, Y. OPT REV (2008) 15: 97. doi:10.1007/s10043-008-0014-z


The optical torque and the trapping position (focal point) in optical tweezers are analyzed for upward-directed focused laser illumination using a ray optics model, considering that laser light is incident at not only the lower surface but also the side surface of a 3-wing rotor. The viscous drag force due to the pressure and the shearing stress on all surfaces of the rotor is evaluated using computational fluid dynamics. The rotation rate is simulated in water by balancing the optical torque with the drag force, resulting in 500 rpm for an SU-8 rotor with 20 μm diameter at a laser power of 200 mW. The trapping position is estimated to be 7.6 μm in the rotor with an upward-directed laser at 200 mW via an objective lens having a numerical aperture of 1.4. Both the rotation rate and the trapping position agree well with the values obtained in the experiment.

Key words

optical tweezers optical torque trapping position drag force rotation rate rotor upward-directed focused beam 

Copyright information

© The Optical Society of Japan 2008

Authors and Affiliations

  • Hiroo Ukita
    • 1
  • Takakazu Ohnishi
    • 1
  • Yasunari Nonohara
    • 1
  1. 1.Faculty of Science and EngineeringRitsumeikan UniversityShigaJapan
  2. 2.Kansai Electric Power CorporationOsakaJapan
  3. 3.Ishida CorporationShigaJapan

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