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A schematic of the experimental setup. The sample cell was made by sticking a rubber o-ring on a microscope cover slip (glass surface) and filled with a dilute colloidal suspension. The components of the optical trapping set-up are the following-Nd-Yag Laser 1064 nm (trapping laser), He–Ne laser 632 nm (particle tracking laser), quadrant photodiode with a 1 KHz bandwidth amplifier, SR830 lock-in amplifier and a three-axis piezostage.
(a) Hologram of a polystyrene sphere. (b) Integrated intensity in a region of around the center of the reconstructed image as a function of d. (c) z-pos (filled circles) from the reconstruction of a stuck sphere as a function of the displacement of the plate in z-direction and x-pos (open circles) from the reconstruction of a stuck sphere as a function of the displacement of the plate in x-direction. Reconstruction of the hologram at (d) units, (e) units, and (f) units.
(a) Real (in-phase) part (b) Imaginary (out-of phase) part (c) ( is the phase difference between the motion of the particle and the container) of the motion of a silica sphere suspended in 200 mM NaCl solution. (d) given by the ratio of and where and are the phase difference between motion of the particle and that of the container at height h and in bulk, respectively.
for (a) silica (open circles) and polystyrene (closed circles) spheres of diameter suspended in 25 mM NaCl solution (b) silica sphere of diameter suspended in 25 mM (open circles), 50 mM (stars), 200 mM (closed circles) NaCl solution (c) polystyrene sphere of diameter suspended in 25 mM (open circles), 50 mM (stars), 200 mM (closed circles) NaCl solution (d) silica sphere of diameters (open circles) and (stars) suspended in 50 mM NaCl solution (e) polystyrene sphere of diameters (open circles) and (stars) suspended in 50 mM NaCl solution. Inset to each panel shows a five-point moving average of the data shown in the main panel.
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