Rotation rate of a three-wing rotor illuminated by upward-directed focused beam in optical tweezers |
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| Authors: | Hiroo Ukita Takakazu Ohnishi Yasunari Nonohara |
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| Institution: | (1) Faculty of Science and Engineering, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8677, Japan;(2) Present address: Kansai Electric Power Corporation, Nakanoshima, Osaka 530-0005, Japan;(3) Present address: Ishida Corporation, Rittoh, Shiga 520-3026, Japan |
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| Abstract: | 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. |
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| Keywords: | optical tweezers optical torque trapping position drag force rotation rate rotor upward-directed focused beam |
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