Dual-beam Interferometric Laser Trapping of Rayleigh and Mesoscopic Particles
There has been a significant amount of experimental work with counter-propagating, crossed-beam, and other interferometric laser trapping of neutral dielectric particles. Apart from the benefits of these configurations, such as the compensation or neutralization of scattering forces, there are a number of interesting applications. For example, the optical lattice resulting from interference can be used to sort particles of different refractive indices or sizes. The system can also be used to study thermal hopping between potential wells or to investigate Brownian motion subject to a quasi-periodic external potential. Most theoretical work on dual-beam systems has been focused on Rayleigh particles. For meso-scopic particles, where Rayleigh scattering is not applicable, we employ the generalized Lorenz-Mie theory (GLMT) which is synonymous with the T-Matrix method when considering spherical particles. GLMT is an exact method which is applicable in both the Rayleigh and mesoscopic regimes. We calculate the fields and optical forces on the particles in the vicinity of the trapping region for several dual beam configurations such as counter-propagating, axially offset, and crossed beams, and with different particle sizes. We present the intensity profiles which demonstrate the interference fringes and the force vectors to predict the positions where a given particle can be localized. Surprisingly, our results show that sub-wavelength localization by interference fringes of particles that are much larger than the wavelength (or fringes) of the trapping beams is possible. The competition between such localization by interference fringes and attraction to the focus can be controlled by the beam convergence angle, or, equivalently, the numerical aperture of the focussing system.
V.L.Y.Loke T.A.Nieminen N.R.Heckenberg H.Rubinsztein-Dunlop
The University of Queensland,Australia
国际会议
Progress in Electromagnetics Research Symposium 2008(2008年电磁学研究新进展学术研讨会)(PIERS 2008)
杭州
英文
1-5
2008-03-24(万方平台首次上网日期,不代表论文的发表时间)