Direct measurement of the nonconservative force field generated by optical tweezers

Author :Pinyu Wu, Rongxin Huang, Christian Tischer, Alexandr Jonas, and Ernst- Ludwig Florin
Publication :Phys. Rev. Lett.
Volume :103
Number :108101
Year :2009

The force field of optical tweezers is commonly assumed to be conservative, neglecting the complex
action of the scattering force. Using a novel method that extracts local forces from trajectories of an
optically trapped particle, we measure the three-dimensional force field experienced by a Rayleigh
particle with 10 nm spatial resolution and femtonewton precision in force. We find that the force field is
nonconservative with the nonconservative component increasing radially away from the optical axis, in
agreement with the Gaussian beam model of the optical trap.