| This thesis describes the design, construction, operation and preliminary calibration of a dual-beam optical tweezers assembly to be used for biophysics experiments. Three-dimensional trapping and steering was demonstrated both with a single trapping beam and with two independent beams. Polystyrene and silica spheres with diameters from one to five micrometers and yeast cells approximately four to six microns across were trapped and manipulated by focusing the 514.5 nm light beam from an Argon ion laser through a 100x microscope objective with 1.3 numerical aperture. Variations with time in the backscattered light collected with a photodiode detector were used to calibrate the axial strength of the trap so that it can be used for force measurements. Preliminary data show the axial spring constant to vary linearly with laser power from 0.74 × 10−6 to 2.87 × 10−6 N/m. |
