Virtual optical pulling force

Progress in light scattering engineering made it feasible to develop optical tweezers allowing capture, hold, and control-lable displacement of submicrometer-size particles and biological structures. However, the momentum conservation law imposes a fundamental restriction on the optical pressure to be repulsive in paraxial fields, which severely limits the capabilities of optomechanical control, e.g., preventing attractive force acting on sufficiently subwavelength particles and molecules. Herein, we revisit the issue of optical forces by their analytic continuation to the complex frequency plane and considering their behavior in the transient regime. We show that the exponential excitation at the complex frequency offers an intriguing ability to achieve a pulling force for a passive resonant object of any shape and composition, even in the paraxial approximation. The approach is elucidated on a dielectric Fabry-Perot cavity and a high-refractive-index dielectric nanoparticle, a fruitful platform for intracellular spectroscopy and lab-on-a-chip technologies, where the proposed technique may find unprecedented capabilities. (c) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement