Optimal wave fields for micromanipulation in complex scattering environments

The manipulation of small objects with light has become an indispensable tool in many areas of research, ranging from physics to biology and medicine(1-7). Here, we demonstrate how to implement micromanipulation at the optimal level of efficiency for arbitrarily shaped targets and inside complex environments such as disordered media. Our approach is to design wavefronts in the far field(8-15) with optimal properties in the near field of the target to apply the strongest possible force, pressure or torque as well as to achieve the most efficient focus inside the target. This non-iterative technique only relies on a simple eigenvalue problem established from the system's scattering matrix and its dependence on small shifts in specific target parameters (access to the near field of the target is not required). To illustrate this concept, we perform a proof-of-principle experiment in the microwave regime, fully confirming our predictions. By designing wavefronts in the far field that have optimal properties in the near field, a general framework for optimal micromanipulation with targets of arbitrary shape and in arbitrarily complex environments, such as disordered media, is reported.