Responsive Spiral Photonic Structures for Visible Vapor Sensing, Pattern Transformation and Encryption

Abstract

Two photon polymerisation using direct laser writing is a burgeoning field of research, with recent focus being placed on bringing added value to microstructures, by incorporating soft, responsive polymers. Moving to the micron‐scale can have a profound impact on such stimuli‐responsive materials, whose speed of actuation can be increased many‐fold compared to their mm‐scale counterparts. Here, the fabrication of submicron 2D photonic structures, based on a vapor‐responsive photoresist with a refractive index <1.55, in the visible wavelength range. The fabricated concentric spiral arrays are evaluated for their feasibility as vapor sensors by testing spectral and structural color reproducibility and reversibility under water, ethanol, isopropanol, and acetone vapors. This approach allows for the realization of predictable uniform color displays that can be modulated upon stimuli response. The transmitted colour in the dry and hydrated states can be accurately modelled. This knowledge is used to design and demonstrate structures for cloaking and image transformation. Such capability can be used for encryption and anti‐counterfeiting applications.

Femtosecond laser direct writing of functional stimulus-responsive structures and applications

“…Apart from the aforementioned stimuli, other external stimuli, including stress [233,234], solvent [235,236], and electric field [237][238][239], can also be used to trigger the dynamic behaviors of intelligent stimulus-responsive structures manufactured by FsLDW technology. For instance, Gräf et al demonstrated the mechanically sensitive surface structural color of LIPSS-based diffraction gratings on ductile austenitic stainless steel through FsLDW.…”

TPL-fabricated responsive hydrogel-based micro photonic structures for visible vapor sensing

“…Figure 3. Consecutive vapor response testing [6]. a) S1 (25 mW laser power), b) S2 (27.5 mW laser power) and c) S3 (30 mW) as a function of exposure time at peak (dotted line) and trough (solid line), respectively.…”

“…Figure 4 Color pixels design and encryption pattern [6]. a) Schematic of 5L spiral photonic structure design with a 0.6 µm thick film underneath (d = 0.5 µm, g1 = g2 = g3 = 2.5 µm).…”

“…We report on 2D multiline micron-scale photonic structures fabricated from an acrylamide-based vapor-responsive photoresist (RI<1.55) using TPL [6][7]. The structures demonstrate reversible and reproducible transmitted visible color change when exposed to a range of vapors.…”

Multilevel Information Encryption Mediated by Reconfigurable Thermal Emission in Smart Bilayer Material

“…Most of the optical characteristics of visible light and their interaction with a variety of external stimuli have been deeply explored to elevate encryption levels. [16][17][18] Therefore, the search for new forms of information encryption and the building of corresponding materials are highly desirable.…”