Lensless focusing and optical trapping

Force mapping of optical gradients associated with electromagnetic fields above subwavelength apertures in a gold thin film has been studied using scanning probe techniques. Vertical cross-sections of this resulting field demonstrate that, in certain conditions, the light emerges in the form of a tightly focused beam even when the incident beam is only weakly focused. Quantification of the near-field in the vicinity of these apertures has shown it is possible to deflect a free particle resulting in an optical trapping effect. Applications involving lensless focusing below the diffraction limit and comparisons with traditional optical tweezing are discussed.