Aberrated optical tweezers for manipulation of microscopic objects

Abstract

Microscopic objects can be manipulated in a more complex and effective way by use of static aberrated tweezers. We theoretically studied dynamics of interaction of Rayleigh particles with such asymmetric tweezers. Microscopic objects are pulled at the high intensity gradient end of the asymmetric tweezers, get accelerated and are ejected from the other end. Thus objects from two locations could be transported by two asymmetric line tweezers and mixed at another place where the low intensity gradient regions of the two beams meet. It is pertinent to note here that the speed of transport is determined by the laser beam power and the degree of asymmetry in the intensity profile. And since for a fixed asymmetry and laser power, the speed is dependent on the refractive index and size of the objects, sorting of these objects could be made possible. Sorting could be achieved either by scanning the asymmetric line tweezers across the sample or without scanning the stage by use of two asymmetric line tweezers. In the all-optical approach (use of two asymmetric line tweezers), we exploited the fact that when the speed of objects transported by one tweezers crossed a threshold value, these did not interact with the second tweezers and therefore moved undeviated; whereas slower moving objects were collected by the second tweezers and transported to a well-separated location.