Fabrication of diffraction based security elements using direct laser interference patterning

Abstract

Product piracy impacts wide areas of the global economy resulting in multi-billion dollar losses per year. Therefore, product protection technologies are required to produce security elements with high flexibility and complexity. In this work, the fabrication of diffraction-based security elements, so called grating cell arrays, using direct laser interference patterning is presented. Ultraviolet two-beam interference patterning is used to structure line-like gratings into 80 µm in diameter spots with spatial periods ranging from 0.7 µm to 2.2 µm on PET substrates. The developed grating cell arrays are generated by the combination of several holographic surface gratings with variable spatial period and pattern orientation. The stored security information can be visualized by illumination with a coherent light source such as a laser pointer.

Dot-Matrix Hologram Rendering Algorithm and its Validation through Direct Laser Interference Patterning

“…The level of product piracy and counterfeiting is increasing every day and demands innovative solutions to fight against it 1 . New anti-counterfeiting methods, utilizing physical unclonable functions 2 , light up-conversion modulation 3 , optical Moirés effects 4 , ripple formation 5 , holograms integrated into low-dimensional electronic devices 6 , metasurface holograms 7 , 8 , etc.…”

“…Historically, this technology used to employ continuous wave lasers of blue or ultraviolet wavelength and corresponding photosensitive materials 10 – 19 , but recent progress in ultrafast lasers has enabled a range of patterning capabilities on virtually any material without the need of photoresists. Direct Laser Interference Patterning (DLIP) technology, employing ultrashort laser pulses, was demonstrated on many different materials, including special inks 20 , polymers 1 , 21 , metals, ceramics, and coatings 22 – 24 . It was also scaled up via roll-to-roll printing 22 , 25 , 26 , but its practical applicability for anti-counterfeiting applications has been rather limited up to now 1 , 20 , 22 .…”

Development of a Monitoring Strategy for Laser-Textured Metallic Surfaces Using a Diffractive Approach

“…Thus, the observed diffraction orders (m = −2, m = −1, m = 0, m = 1 and m = 2 as indicated in Figure 3c) correspond to the DLIP structures, while the additional features observed (exemplary the vertical distributed intensity peaks for m = 0 in Figure 3c) correspond to the larger repetitive patterns, which in turn correlate with both the used hatch and overlap distances. Additional information regarding the complex diffraction patterns observed can be found in [42,43]. correspond to the DLIP structures, while the additional features observed (exemplary the vertical distributed intensity peaks for m = 0 in Figure 3c) correspond to the larger repetitive patterns, which in turn correlate with both the used hatch and overlap distances.…”

“…correspond to the DLIP structures, while the additional features observed (exemplary the vertical distributed intensity peaks for m = 0 in Figure 3c) correspond to the larger repetitive patterns, which in turn correlate with both the used hatch and overlap distances. Additional information regarding the complex diffraction patterns observed can be found in [42,43]. In order to quantitatively characterize the homogeneity of the different periodic structures as function of the used hatch distances and overlaps, both the mean structure depth of the periodic structures, corresponding to the interference pattern (called from now on "first modulation", Zfm) as well as the structure height of the larger surface structure (denoted as "second modulation", Zsm) were determined.…”

Large-Beam Picosecond Interference Patterning of Metallic Substrates

“…Direct laser interference patterning (DLIP) provides a solution to these issues by overlapping two or more coherent laser beams on the surface to directly imprint an interference pattern. If enough pulse energy is used, a large variety of materials can be processed at interference maxima positions, including metals [ 16 , 17 , 18 ], dielectrics [ 19 , 20 ], and even composite materials [ 21 ]. This allows the patterning of an area on the order of several tens of µm in diameter in a single irradiation step and with resolutions below the diffraction limit of the initial beam.…”