Low‐threshold organic microlasers are demanded for advanced optical applications such as nano/micrometer scale memory, sensing, and communication tools, and further valuable for future electrically driven laser applications. In this paper, it is demonstrated that various highly fluorescent conjugated polymers self‐assemble to form single‐component microspheres that exhibit, upon femtosecond pumping to a single microsphere, whispering gallery mode (WGM) lasing with blue, green, and red emission colors. In particular, the microsphere consisting of polyfluorene shows the lowest threshold fluence as low as 1.5 µJ cm−2 and high photostability against successive pumping of >105 pulse. The threshold fluence is further reduced by one fourth (0.37 µJ cm−2) by mounting the microspheres on an Ag‐coated substrate, where a mirror effect of the Ag layer enhances efficiency of the photoluminescence confinement with a minor effect of plasmonic near‐field. Considering the intrinsic charge injection and transport properties, π‐conjugated polymer microsphere resonators will be possible materials for electrically pumped WGM luminescence.

Photochromic microresonator arrays with whispering gallery mode fingerprints are successfully prepared, which function as high-security optical authentication microdevices.

Metasurfaces comprising 3D chiral structures have shown great potential in chiroptical applications such as chiral optical components and sensing. So far, the main challenges lie in the nanofabrication and the limited operational bandwidth. Homogeneous and localized broadband near‐field optical chirality enhancement has not been achieved. Here, an effective nanofabrication method to create a 3D chiral metasurface with far‐ and near‐field broadband chiroptical properties is demonstrated. A focused ion beam is used to cut and stretch nanowires into 3D Archimedean spirals from stacked films. The 3D Archimedean spiral is a self‐similar chiral fractal structure sensitive to the chirality of light. The spiral exhibits far‐ and near‐field broadband chiroptical responses from 2 to 8 µm. With circularly polarized light (CPL), the spiral shows superior far‐field transmission dissymmetry and handedness‐dependent near‐field localization. With linearly polarized excitation, homogeneous and highly enhanced broadband near‐field optical chirality is generated at a stably localized position inside the spiral. The effective yet straightforward fabrication strategy allows easy fabrication of 3D chiral structures with superior broadband far‐field chiroptical response as well as strongly enhanced and stably localized broadband near‐field optical chirality. The reported method and chiral metasurface may find applications in broadband chiral optics and chiral sensing.

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Historically, the field of plasmonics has been relying on the framework of classical electrodynamics, with the local-response approximation of material response being applied even when dealing with nanoscale metallic structures. However, when the confinement of electromagnetic radiation approaches atomic scales, mesoscopic effects are anticipated to become observable, e.g., those associated with the nonlocal electrodynamic surface response of the electron gas. Here, we investigate nonlocal effects in propagating gap surface plasmon modes in ultrathin metal–dielectric–metal planar waveguides, exploiting monocrystalline gold flakes separated by atomic-layer-deposited aluminum oxide. We use scanning near-field optical microscopy to directly access the near-field of such confined gap plasmon modes and measure their dispersion relation via their complex-valued propagation constants. We compare our experimental findings with the predictions of the generalized nonlocal optical response theory to unveil signatures of nonlocal damping, which becomes appreciable for few-nanometer-sized dielectric gaps.