Chiral polariton lasing offers a circularly polarized and energy-efficient source of coherent light. Achieving strong optical contrast between opposite circular polarizations, however, remains difficult due to the weak circular dichroism of excitonic gain materials at room temperature. Additionally, creating highly chiral lasing typically requires breaking the symmetry of optical cavities, which can degrade resonance quality and reduce chiral purity. In this work, we demonstrate that plasmonic nanoparticle lattice cavities composed of mismatched dimer unit cells, when strongly coupled to CdSe nanoplatelets, enable polariton lasing with both a low threshold fluence (8 μJ/cm²) and high chiral purity (∼0.92). The lasing threshold is at least twice as low as other reported systems operating at room temperature, and the degree of chirality approaches theoretical limit. These features make our polaritonlasing a compelling candidate for diverse applications in spintronics, optoelectronics, and quantum information technologies.
