Enhanced Second Harmonic Generation in Double‐Resonance Colloidal Metasurfaces

A key challenge for optical circuits is the ability to integrate nonlinear optical signal processing components such as optical modulators and frequency mixers at the chip scale. Optical antennas that focus light into nanoscale volumes can be utilized to shrink the footprint and increase the efficiency of these components. Multiresonant antennas that enhance both optical absorption and emission process are recently demonstrated to enable efficient nonlinear frequency conversion at the nanoscale and are promising as structures for second harmonic generation (SHG) and upconversion. Here, the ability of colloidal metasurfaces fabricated by self‐assembly as on‐chip platforms for enhanced SHG is demonstrated. These metasurfaces exhibit high spatial overlap of multiple surface plasmon modes whose frequencies can be independently tuned through appropriate design of colloidal and metasurface geometries. It is demonstrated that these bottom‐up structures rival lithographic nonlinear optical antennas in SHG efficiency, suggesting the potential for these colloidal metasurfaces in integrated on‐chip architectures.