Calculation Model Of Optical Tweezers And Analysis Of Axial Trapping Force

The study on optical tweezers is an interdisciplinary sciences that containphysics, biology, chemistry, medicine and materials etc. It is difficult forindividual to study further due to the complexity of optical tweezerstechnology. We have only to delve it into from a small point, and thencontribute ourselves to the entire optical tweezers technology research.Optical tweezers must aim at the practical application as a technical means,however, its theory research is also important. The detour in the process ofoptical tweezers research will be avoided with a profound theory basis. Themost important function of optical tweezers is the manipulation inmicron-sized scale and the measurement of tiny force, which requires aquantitative understanding of the trapping force. There are many methods inprevious discussions about the quantitative study of optical tweezers, and theray-optics model is one of them. Here we analysis the trapping performance ofoptical tweezers based on ray-optics model.Optical tweezers is a complex system, so that all possible factors that affectthe performance of optical tweezers must be considered, such as property oflight source, parameters of experiment equipment, design of experimentalprocess, selection of experimental objective etc.The effect of spherical aberration on trapping force of optical tweezers wasdiscussed by the calculation results in ray-optics model here firstly. Theresults shows that the backward pull force was weaken because of theexistence of spherical aberration, moreover, the weaken level of theperformance of optical tweezers was under the influence of the change ofnumerical aperture and detective depth, and both of them were key parametersin optical tweezers.Secondly, the importance of trapping light source of optical tweezerssystem in trapping processing was also considered. The Gaussian beam and Laguerre-Gaussian beam are worked as trapping light source respectively toanalyze the difference of trapping results. According to the calculation results,Laguerre-Gaussian beam could provide better trapping performance, andbesides, the trapping performance of Laguerre-Gaussian beam would bereduced with the increase of numerical aperture to high value under the effectof spherical aberration.In addition, the trapping performance of double-layer dielectric sphere wasstudied. By analyzing the calculation results, we can obtain the relationshipbetween trapping force of double-layer sphere and the ratio of inner layerradii to the outer layer, the other parameters that the ratio of inner layerrefractive index to outer layer, numerical aperture of convergent lens anddetective depth of optical trap.Finally, acoustic tweezers and magnetic tweezers were introduced, andcomparied with optical tweezers. The results could provide new ideas for thefuture development of optical tweezers.