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Figure 1: Schematic diagram of typical optical tweezer implementation. A Gaussian laser beam is directed into the back aperture of a high numerical aperture objective lens and brought to a tight focus. A dielectric particle is drawn up intensity gradients toward the focus but is displaced somewhat by radiation pressure. The same objective lens used to trap the particle also can be used to image it.

Figure 2: Pair interaction potentials measured for spheres of diameters 1.53 tex2html_wrap_inline718 m, 0.97 tex2html_wrap_inline718 m, and 0.65 tex2html_wrap_inline718 m. The three populations of charge-stabilized latex spheres were dispersed in the same suspension so that their interactions would be characterized by the same screening length. Solid lines are fits to the DLVO potential for the screening length, the spheres' effective charge numbers. Curves are offset for clarity. Adapted from Ref. [35].

Figure 3: Pair interaction potential for 0.65 tex2html_wrap_inline718 m diameter latex spheres at two different separations from a charged glass wall. The interaction is purely repulsive at a height of 9.5 tex2html_wrap_inline718 m (top curve), but develops an attractive minimum when the spheres are 2.5 tex2html_wrap_inline718 m from the wall. Reproduced from Ref. [40].

David G. Grier
Mon Feb 17 21:35:47 CST 1997