Investigation On The Optical Tweezer System Based On Photophoretic Force

The optical tweezer is a new micro-manipulation technology developed from the1970s. It utilizes the forces generated from the interaction between light and matters to manipulate micro matters and belong to a kind of non-contact manipulation technology. Due to its features of high precision and simply structure, the optical tweezer has been applied widely in regions of physic, chemistry, biology, material, and etc.. These optical tweezer systems can be devided into two types:one type is based on radiation pressure and gradient force, and can be applied to manipulate transparent particles and reflective particles to improve the researches about biological cells, organelles, biomolecules, colloidal particles and metal nanoparticles. The other one is based on photophoretic force and can be applied to manipulate the absorbing particles in gas. It has gradually got the attentions of researchers in recent years. This kind of optical tweezer system has important potiential applications in the researches about the dynamic behavior of the aerosols in atmospheric science and the movement of the dust in planetary science. In this paper we conducted some researches about the optical tweezer technology based on photophoretic force.We designed taper-ring optical traps by a weakly focused laser beam through a circular aperture and proposed the feasibility of trapping light-absorbing particles. The optical tweezers system was set up and the intensity profile of the optical traps was identified. The particles’revolving around the optical axis was realized and the reason of particles’revolving is analyzed qualitatively. The frequency of revolving can be controlled by changing the laser power in the experiments. It was demonstrated that multiple particles can revolve simultaneously in different planes perpendicular to the optical axis and be moved integrally on three-dimensional directions flexibly. The revolving diameters of the particles are different and the biggest diameter can reach700micrometer. In the experiments, different moving orbits of the particles can be gained by using different apertures.Moreover, we used the above optical tweezer system to trap a large number of particles and analyzed their dynamic behavior in different laser powers. The distributive characters of different kinds of particles are compared experimentally and analyzed. To strengthen the binding of the particles on the axial direction and realize the agglomeration of particles, the dual-beam optical tweezer system is built. We realized the agglomeration of particles and observed the phenomenon of the rotation of the particle in the intersection region of two counter-propagating beam.We built up the holographic optical tweezer system based on the liquid crystal spatial light modulator and compared experimentally the phase modulating result of the incident beam with different polarizations. The kinoform is employed to realize the vortex beam with different topological charge to trap multiple light-absorbing particles.