非线性晶体产生的空心光束中大尺寸粒子囚禁与导引

提出了一种基于非线性ZnSe晶体产生的空心光束与光泳力的大尺寸粒子二维囚禁与一维导引、三维囚禁方案.理论上分析并计算了单个非线性ZnSe晶体产生的空心光束内粒子受到的横向与纵向光泳力,纵向光泳力的大小同粒子尺寸与光束尺寸比例的四次方成正比,与空心光束功率成正比,方向与光束传播方向一致.粒子尺寸与空心光束尺寸越接近时,横向光泳力的大小越大.结果表明该光泳力可以实现对大尺寸粒子的二维囚禁,同时可对粒子进行长距离(米量级)一维定向导引;理论上分析并计算了基于双非线性ZnSe晶体产生的局域空心光束内粒子所受横向与纵向光泳力情况,光泳力与系统参数的依赖关系与单个非线性晶体产生的空心光束中的粒子受力情况类似,不同的是该条件下纵向光泳力指向光束中心.结果表明该局域空心光束可以实现大尺寸粒子的三维有效囚禁.基于非线性ZnSe晶体产生的空心光束或者局域空心光束可以作为大尺寸粒子非接触式有效操控的工具,在现代光学以及生物医学中有潜在的应用.

Trapping and guiding of large-size particles in hollow beams produced by nonlinear crystals

Since 1970, the trapping of the small objects in space by optical radiation pressure, such as nano particles and other atomic living cells, has been successfully developed and used in the applied physics, life sciences and other fields. As the optical radiation pressure is very weak, the use of radiation pressure on the particle will be strictly limited by the particle size. Also, the manipulated particles can move particle with only hundreds of microns. Therefore, it is not suitable for trapping and long-distance transporting particles with large size (micron). In recent years, with the development of the manipulation technology for large particles, a new control force-photophotetic force has gradually entered into people's vision field. Compared with the optical radiation pressure, the photophoretic force is much large under the same light intensity. Therefore, the photophoretic force makes it possible to manipulate and trap the large particles. With the development of laser beam-shaping technology, the species of laser beams become more and more abundant, which makes it more attractive to study particle manipulation based on the photophoretic force. For example, a hollow beam is used to capture and guide carbon nanoclusters in the air. A tapered optical fiber is used to trap, migrate and separate SiO₂ particles. A Bessel Gaussian beam is used to trap and manipulate magnetic particles. An airy beam is used to trap glass carbon particles of absorption type. In this paper, a trapping and guiding scheme for large-size particles by using the photophoretic force of the hollow beams generated by nonlinear ZnSe crystals is proposed and analyzed theoretically. Our calculated results can be concluded as follows. 1) For the cases of two-dimensional particle trapping and one-dimentional particle guiding using a hollow beam generated by a single nonlinear ZnSe crystal, the magnitude of the longitudianl optical force is proportional to the ratio between particle size and hollow beam size to the fourth power and is proportional to the power of the hollow beam, and the direction is the same as that of the beam propagation. The closer to the hollow beam size the particle size, the greater the transverse optical force is. The results show that the photophoretic force can achieve the two-dimensional trapping of large-size particles, and a long distance (in a meter region) guiding. 2) For the case of three-dimensional particle trapping using a localized hollow beam generated by two nonlinear ZnSe crystals, the dependence of transverse photophoretic forceand that of longitudinal photophoretic force on the system parameters are similar to the scenario for the particles trapping in the hollow beam produced by a single nonlinear crystal. The difference is that under this condition, the direction of the longitudinal photophoretic force points to the center of the beam. So this scheme can achieve the effective three-dimensional trapping of large-size particles. Above all, the hollow beams generated by nonlinear ZnSe crystals can be used as an effective noncontact controlling tool for large-size particels, and might have potential applications in modern optics and biomedicine.