The Focusing Path And Imaging Path Separated Optical Tweezers

Optical tweezers use the forces exerted by a strongly focused beam of light to capture and manipulate micro-particles. Because of optical tweezers can noninvasively manipulate microscopic objects in a high-precision way, from its inception there has been a rapid development and wide application. As an important research tool the optical tweezers have been successfully applied to biological, physical, medical and other areasIn common optical tweezers system the focusing setup and the imaging setup share the same objective lens. Such an optical arrangement allows the observation only in the two-dimensional focal plane. The goal of this work is to build up an optical tweezers system in which the focusing path and imaging path are separated by using two objective lenses. Through the separated focusing and imaging, we can flexibly observe the spatial distribution of the trapped particles as well as the optical field distribution of the focused laser. This article contains the following contents. First, we briefly review the history, background and the progress of researches related to the optical tweezers. The rudimental principles of the laser trapping technique, including radiation pressure, scattering force, gradient force and optical trap are then introduced. The optical trapping forces exerting on Mie particles and Rayleigh particles are analyzed. The self-built optical tweezers system with the separated focusing and imaging paths are described in details, following by the analysis of the advantages and disadvantages of our system compared with the conventional system. Finally, we perform the optical experiments on particle trapping with our self-built optical tweezers. The optical trapping of particles has been realized by using a focused Gaussian beam. The trapping process of particles using the vortex beams with different topological charges has been also observed.