Synchronization of optically self-assembled nanorotors.

Self-assembly of nanoparticles by means of interparticle optical forces provides a compelling approach toward contact-free organization and manipulation of nanoscale entities. However, exploration of the rotational degrees of freedom in this process has remained limited, primarily because of the predominant focus on spherical nanoparticles, for which individual particle orientation cannot be determined. Here, we show that gold nanorods, which self-assemble in water under the influence of circularly polarized light, exhibit synchronized rotational motion at kilohertz frequencies. The synchronization is caused by strong optical interactions and occurs despite the presence of thermal diffusion. Our findings elucidate the intricate dynamics arising from the transfer of photon spin angular momentum to optically bound matter and hold promise for advancing the emerging field of light-driven nanomachinery.

Lasing Action in Single Subwavelength Particles Supporting Supercavity Modes.

On-chip light sources are critical for the realization of fully integrated photonic circuitry. So far, semiconductor miniaturized lasers have been mainly limited to sizes on the order of a few microns. Further reduction of sizes is challenging fundamentally due to the associated radiative losses. While using plasmonic metals helps to reduce radiative losses and sizes, they also introduce Ohmic losses hindering real improvements. In this work, we show that, making use of quasibound states in the continuum, or supercavity modes, we circumvent these fundamental issues and realize one of the smallest purely semiconductor nanolasers thus far. Here, the nanolaser structure is based on a single semiconductor nanocylinder that intentionally takes advantage of the destructive interference between two supported optical modes, namely Fabry-Perot and Mie modes, to obtain a significant enhancement in the quality factor of the cavity. We experimentally demonstrate the concept and obtain optically pumped lasing action using GaAs at cryogenic temperatures. The optimal nanocylinder size is as small as 500 nm in diameter and only 330 nm in height with a lasing wavelength around 825 nm, corresponding to a size-to-wavelength ratio as low as 0.6.