Optical tweezers is a new technique for research in biological and physical sciences by using the radiation pressure. In this thesis, a diode laser, A = 785nm, maximum power=50mW, was used as the light source and a microscope was used for trapping and imaging. The laser pass through an anamorphic prism and provide an ideal Gaussian laser profile. Before reflecting the laser beam into the microscope, a beam expander and a convex lens expand and change the divergent angle of the laser beam for maximum power delivery and matching the imaging plane of the microscope. The trapped object was illuminated by the condenser and formed an image on a charge-coupled device (CCD) through a hot mirror. A laser line filter put in front of the CCD to avoid the exposure saturation by the laser light. The images from the CCD were monitored on the screen and trapped with a recorder.
We have built and tested an optical tweezers system, which successfully trapped latex particles and yeast of radius ranging from 1 to 20 μm. And we also achieved dual trap optical tweezers to trap and rotate two particles at the same time.