Hierarchical Fourier Surfaces via Broadband Laser Vectorial Interferometry

The ever-growing demand for submicrometer-structured surfaces with hierarchical features is guided by efficient applications in augmented/virtual reality, display technologies, and Fourier optics, as well as for the development of multifunctional platforms for biomedicine, sensors, and security. Among all, Fourier surfaces still represent a challenge. Indeed, the current technologies are mainly based on multistep processes which involve lithographic methods and/or thermal/chemical/electrical treatment and often suffer in terms of losses due to their intrinsic binary design. Herein, a broadband laser composed of close and highly correlated lines allows for the simultaneous photoinscription of extremely precise hierarchical Fourier surfaces via vectorial interference. By simply setting the number of lines, their amplitude, and polarization, the polychromatic light enables a high-fidelity encoding of multiple sinusoidal profiles with nanometric spatial resolution. Beat phenomena that arise in the bulk of the recording medium result in the never-observed hierarchical structuring of the topography. Such an approach, unconventional for holographic techniques where monochromaticity of light is a key element, provides promising perspectives for the in situ design of hierarchical Fourier surfaces and the scale-up of customized structured platforms, besides the obvious advantages of the method in terms of scalability, reconfigurability, and tunability.