Perspective of Multi-wavelength Optical Patterning for Topographical Design

Driven by the strong interest in the design and manufacturing of structured topographies with related functionalities, great attention has been addressed in finding efficient fabrication methods. Between them laser interferometry is a consolidated technique for materials structuring, enabling single step and large area patterning. Here we report the investigation of the morphological modification induced on the surface of a thin film of a photosensitive material by the light interference pattern obtained from a laser operating in multiline mode [1]. Such light beam enables an accurate encoding of multiple sinusoidal profiles by setting the number of lines, their amplitude and the crossing angle of the interfering beams. An azopolymer is exploited as medium for the holographic recording [2]. AFM investigation has been performed to study the modification induced on the surface of the irradiated area. Patterns at different length scales are achievable in a single step, that can be traced back from the laser lines combination. By considering the case of four lines with equal intensity, the optical structures recorded on the sample surface replicate both small scale sinusoidal modulations related to the beam wavelengths and beat envelope at large scale. The Fourier analysis of the surface relief profile, whose shape is mediated by the photomechanical response of the material [3], matches the Fourier components of the light pattern. The proposed multi-wavelength holographic patterning provides a simple tool to generate complex structures, such as optical Fourier surfaces, able to create multifunctional platform for biology and medicine, tissue engineering and anti-counterfeiting methods. REFERENCES 1. Audia, B., P. Pagliusi, A. Mazzulla, and G. Cipparrone, "Multi-wavelength optical patterning for multiscale materials design," Photonics, Vol. 8, No. 11, 481, 2021. 2. Oscurato, S. L., M. Salvatore, P. Maddalena, and A. Ambrosio, "From nanoscopic to macroscopic photo-driven motion in azobenzene-containing materials," Nanophotonics, Vol. 7, 1387- 1422, 2018. 3. Audia, B., P. Pagliusi, C. Provenzano, A. Roche, L. Oriol, and G. Cipparrone, "Influence of photoanisotropies on light-controllable structuration of azopolymer surface," ACS Appl. Polym. Mater., Vol. 2, 1597-1604, 2020