Fig. 2.

Plots of measured scattered light intensity vs. height for a 3-μm bead above the surface of a glass microscope slide. Red: Using a 637-nm wavelength optical tweezer. Blue: Using a 785-nm wavelength optical tweezer. (A) No AR coating: The step-like behavior is due to formation of a standing-wave component in the optical trap due to reflection from the glass–water interface. The plots are shifted vertically for clarity. (B) AR coated: The reflection is eliminated and the bead is able to step smoothly toward the surface.