Abstract
A physical model is presented to understand and calculate trapping force exerted on a dielectric micro-particle under focused evanescent wave illumination. This model is based on our recent vectorial diffraction model by a high numerical aperture objective operating under the total internal condition. As a result, trapping force in a focused evanescent spot generated by both plane wave (TEM00) and doughnut beam (TEM*01) illumination is calculated, showing an agreement with the measured results. It is also revealed by this model that unlike optical trapping in the far-field region, optical axial trapping force in an evanescent focal spot increases linearly with the size of a trapped particle. This prediction shows that it is possible to overcome the force of gravity to lift a polystyrene particle of up to 800 nm in radius with a laser beam of power 10 microW.
Highlights
Small particle trapping and manipulation based on the radiation pressure mechanisms has been demonstrated for quite some time [1]
A physical model is presented to understand and calculate trapping force exerted on a dielectric micro-particle under focused evanescent wave illumination
This model is based on our recent vectorial diffraction model by a high numerical aperture objective operating under the total internal condition
Summary
Small particle trapping and manipulation based on the radiation pressure mechanisms has been demonstrated for quite some time [1]. The third near-field trapping category demonstrated recently [13] is based on the use of a focused evanescent field produced by a high NA objective with a central obstruction The size of the obstruction is large enough to ensure that the minimum angle of convergence of each incident ray is larger than the critical angle determined by the total internal reflection condition between two media. This method leads to the reduced trapping volume and offers additional advantages over other near-field trapping methods in terms of the heating and the distance regulation problems. Based on the scattering process of a small particle with the evanescent focal spot, one can determinate the electromagnetic field inside and outside a particle [8] and the trapping force exerted on the particle [9]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
