title: Axial optical trapping efficiency through a dielectric interface.
abstract: Axial trapping through a dielectric interface is investigated in the framework of the angular spectrum representation and of the generalized Lorenz-Mie theory. We determine the optical force for an arbitrarily polarized non-paraxial, strongly aberrated, axially symmetric focusing beam and apply this description to the case of an arbitrarily positioned dielectric microsphere, commonly employed in optical tweezers, not taking into account the contribution of evanescent waves at the interface. We derive the analytical expression of the force profile, finding that the incident polarization does not affect the axial optical force. In addition, we derive an approximated expression for the axial force as a function of beam displacement just outside the microsphere and we show how the information provided by the ripple structure of the optical trapping efficiency versus sphere displacement curve, due to the aberration effect, could be exploited to calibrate the bead axial position versus the experimental beam positioning controls.
authors.affiliation: National Nanotechnology Laboratory of CNR-INFM, Università del Salento, c/o Distretto Tecnologico ISUFI, via Arnesano I, Lecce, Italy. antonio.neves@unile.it
authors.forename: Antonio Alvaro Ranha
authors.initials: AA
authors.lastname: Neves
authors.forename: Adriana
authors.initials: A
authors.lastname: Fontes
authors.forename: Carlos Lenz
authors.initials: CL
authors.lastname: Cesar
authors.forename: Andrea
authors.initials: A
authors.lastname: Camposeo
authors.forename: Roberto
authors.initials: R
authors.lastname: Cingolani
authors.forename: Dario
authors.initials: D
authors.lastname: Pisignano
mesh_terms: D001703:Biophysics / Q000379:methods*; D002138:Calibration; D004563:Electrochemistry / Q000379:methods; D004867:Equipment Design; D019563:Mechanics; D008846:Micromanipulation; D008853:Microscopy; D008863:Microspheres; D015233:Models, Statistical; D008962:Models, Theoretical; D055095:Optics and Photonics; D012031:Refractometry