Spin and Orbital Angular Momentum Lasing from Phase-gradient Plasmonic Lattices.

Controlling polarization, wavefront profile, and directionality of lasing emission is critical for advancing optical technologies. However, realizing independent tunability over each characteristic within a single cavity design is challenging. Specifically, polarization resulting from spin angular momentum needs the symmetry of the cavity mode to be broken, while beam profiles from orbital angular momentum need the symmetry to be maintained. Although dielectric metasurfaces having geometric phase gradients are a compact approach to customize wavefronts, they often lack the high-quality cavity modes needed for lasing. Here we show plasmonic cavities can support phase-gradient lattice resonances with unity circular polarization at engineered positions in Fourier space. Excitons from CdSe nanoplatelets can strongly couple to these chiral cavity modes and generate photoluminescence with near-unity chirality from lower polariton emission. Low-threshold, simultaneous lasing from multiple beams was achieved at angles defined by nanoparticle rotation within the phase gradient. The combined orbital and spin angular momentum properties within the same beam highlight how localized plasmons can engineer phase singularities and geometric phase separately in the same cavity resonance.