Optical Trapping And Manipulation Of Mie Particles By Airy Evanescent Wave

With the never-ending changes and improvements of science and technology, more and more attention has been paid into the optical tweezers based on laser technology. Since Ashkin et al. proved that three-dimensional trapping of a dielectric particle is possible by use of a single, highly focused laser beam [1], optical tweezers have become an indispensable tool for manipulating small particles. Currently optical tweezers have found numerous applications in the fields of biology, chemistry, and physics. Optical tweezers are sub-contact, pollution-free and noninvasive, then can be used to manipulate live cells. That is to say using a tightly focused beam, we can accelerate, decelerate, even trap nanoparticles and microparticles. Physicists have studied optical trapping and manipulation of microscopic particles with traditional plane wave and focused Gaussian beam theoretically and experimentally. Recently, the experimental realization of Airy beam, can be well applied into the conventional optical tweezers, which can avoid divergence and diffraction within a certain propagating distance for its unique features:"non-diffracting", transverse acceleration and self-healing properties.In this article, using vector potential and Fourier transform spectrum representation, we investigate the one-and two-dimensional Airy beam propagating through an interface. And the Airy evanescent field in the upper medium formed by total internal reflection when the incident angle is larger than the critical angle. Numerical results show that the Airy evanescent wave dies away several wavelengths away from the interface. Utilizing the generalized Lorenz-Mie theory, we investigate the scattering of the Airy evanescent field by a spherical dielectric particle, the optical forces exerted on the Mie particle, and simulate the motion trajectory of the particle. Numerical results show that the optical forces exhibit strong oscillations which are corresponding to the distributions of the evanescent field. With the increasing the size of particle radius, Morphology Dependent Resonance (MDR) occurs for the particle with specific refractive index.Morphology-dependent resonance (MDR) of the optical forces for a particle illuminated by Airy beams is investigated with respect to its internal field distribution. We find the quality factor Q of the resonant peaks for a damped wave is much larger than that for a propagating wave. The ring structures arising from the resonance transform significantly with the parametric evolution of Airy evanescent wave, and the interference of the internal waves have a great impact on the Q factor and the background of the resonant peak, e.g., travelling wave patterns correspond to high Q peaks, while strong interference patterns for high background peaks. But the key structure of the internal field for the Airy transmitted wave won’t change.The multiple reflections of the evanescent wave between the particle and the interface are also investigated, which show significant impacts on the region where the energy concentrate in. We also analyzed the enhancing of the Airy evanescent wave by the surface plasmon resonance (SPP) the metal film covered on the interface. Numerical results show that when SPP resonance occurs, the intensity of the Airy evanescent field is enhanced by one order of magnitude, the distribution of the evanescent field is localized, the corresponding optical force increases two orders of magnitude.