Spectrally Encoded Proximity‐Field Nanopatterning

ABSTRACT Three‐dimensional (3D) photonic crystals offer unprecedented control over optical properties, yet their practical application is impeded by a fundamental trade‐off: top‐down fabrication methods offer high designability but limited scalability, while scalable bottom‐up approaches lack design freedom. Proximity‐field nanopatterning, a form of phase‐mask‐assisted interference lithography, presents a scalable path to bespoke 3D photonic crystals. Here, we introduce spectrally encoded proximity‐field nanopatterning (SEPN), which enables continuous, mask‐lenient control over the 3D aspect ratio of nanostructures by utilizing the exposure wavelength as a dynamically tunable parameter. By modulating the exposure wavelength, we achieve independent control over the out‐of‐plane periods of the photonic crystals while keeping the in‐plane periodicity fixed. This technique allows for the precise and independent engineering of near‐infrared (NIR) reflectance bands, effectively decoupling them from the visible iridescence angles governed by the fixed in‐plane period. We demonstrate the versatility of SEPN by sequentially printing different nanopatterns to create a multipattern device. This device displays a hidden, multi‐spectral image in the NIR while remaining visually unobtrusive, suggesting the utility of SEPN for advanced security and anticounterfeiting applications.