Optical tunnels: long-range optical trapping and manipulation in aqueous media

In this study, we demonstrate an asymmetric counter-propagating beam system with engineered optical forces allowing for long-range particle trapping and manipulation. We achieved this by breaking the symmetry of the well-known counter-propagating optical trapping beams. By doing so, we extend the range of optical forces for particle confinement and transportation to significantly larger foci separations, creating an optical tunnel. These tunnels are capable of moving matter forward and back with controllable speeds for more than a millimeter length with the ability to bring them to a full stop at any point, creating a stable 3D trap. Our trap stiffness measurements for the asymmetric trapping system demonstrate at least one order of magnitude larger values with respect to the symmetric counter-propagating beams so far reported. Our system is quite versatile as it allows for single or multi trapping with flexible positioning of any size particle ranging from tens of nanometers to tens of microns with powers as low as a few milliwatts.