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Monday, December 14, 2009

Wavelength dependence of optical tweezer trapping forces on dye-doped polystyrene microspheres

M. J. Kendrick, D. H. McIntyre, and O. Ostroverkhova

We present an experimental and numerical study of the wavelength dependence, near resonance, of the optical tweezer trap stiffness on three different dye-doped 1 μm polystyrene spheres with peak absorptions at λ=625, 775, and 840 nm. Experimentally, an increase in the trap stiffness of ~35% on the red side of resonance was observed for the dye-doped spheres relative to polystyrene spheres without dye. Numerical simulations for spheres of different sizes, between 20 nm and 1 μm, and for absorption strengths corresponding to peak extinction coefficient values between 0.0027 and 0.081 were also conducted. Numerical results showed a maximum increase in the trap stiffness of ~35%, which is consistent with experimental results.

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