We present a novel method for characterising nanoparticles through analysis of their light scattering. We examine the resultant angularly resolved Rayleigh scattering patterns by aligning and orienting single optically levitated nanoparticles in a vacuum with trapping light. We compare our experimental findings with simulations of the Rayleigh scattered field, which allow us to determine in-situ the morphology of individual nanoparticles. While primarily utilized in low-damping environments, this method can also be applied in traditional overdamped fluids, paving the way for precision measurements of single isolated nanoparticles.
The isolation afforded by levitated optomechanics, combined with the ability to detect ultraweak forces in three directions, makes them particularly interesting for directional dark searches. This directionality allows 3D reconstruction of an interaction with increased background rejection, even with only a few detection events. We will discuss a levitated sensor that is being developed to place new bounds on composite dark matter by detecting their collisions with trapped nanoparticles. We will describe the 3-D electrical cold damping scheme used in this experiment as well as the electrode configuration that allow us to provide a well-defined directional impulse calibration. We will also present a preliminary analysis of the first experimental data run that is currently underway.
The optical centrifuge is an established tool in molecular physics for inducing controlled rotation of molecules through the transfer of angular momentum from an optical field. Here the polarization vector is rapidly rotated up to high angular velocities, which subsequently rotates molecules up to high angular frequencies. This technique has been instrumental in studying molecular structure and collision processes. Recently, there has been significant interest in controlling the rotational motion of nanorotors to study non-classical states in these macroscopic systems.
We describe the creation of an optical centrifuge for nanorotors formed by anisotropic nanoparticles levitated within an optical tweezer. We present a classical description of this process and discuss optimal schemes for the acceleration of the linear polarization vector to well-defined rotational frequencies. We report on the experimental realization of the centrifuge enabled by a fast in-line polarization controller. This approach is also compared to rapid switching between linear and elliptically polarized fields. Finally, we describe future experiments to probe the quantum nature of rotation in these systems.
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