Analysis of trapping forces combining near-field optical tweezers with AFM probe

Recently, interest in nano-manipulation using the evanescent wave generated by near-field optical probes has been growing. The possibility of using the metallic tip of an atomic force microscope illuminated by evanescent wave from a fiber probe to create optical tweezers for selective manipulation of nano-particles is explored. A generalization of the conservation law for momentum using three-dimensional finite difference time domain method for rigorous calculations is applied to analyze near-field trapping forces. Calculations show that the scheme is able to trap smaller particle with lower laser intensity than that required by conventional near-field optical tweezers. The trapping potential is sensitively dependent on the distance between two probes and incident angle, as well as the incident polarization direction and wavelength. Based on the high manipulation efficiency and the high resolution of AFM system, the scheme allowing for effective and accurate manipulation of nano-particles opens a way for research on single nano-particle area.