Laser microsculpting for the generation of robust diffractive security markings on the surface of metals

Abstract

a b s t r a c tWe report the development of a laser-based process for the direct writing ('microsculpting') of unique security markings (reflective phase holograms) on the surface of metals. In contrast to the common approaches used for unique marking of the metal products and components, e.g., polymer holographic stickers which are attached to metals as an adhesive tape, our process enables the generation of the security markings directly onto the metal surface and thus overcomes the problems with tampering and biocompatibility which are typical drawbacks of holographic stickers. The process uses 35 ns laser pulses of wavelength 355 nm to generate optically-smooth deformations on the metal surface using a localised laser melting process. Security markings (holographic structures) on 304-grade stainless steel surface are fabricated, and their resulted optical performance is tested using a He-Ne laser beam of 632.8 nm wavelength.

Experimental investigation and optimisation of laser direct part marking of Inconel 718

“…In the present study, although there are similarities with the aforementioned studies [35,36] , the operation of the laser in a scanning instead of steady mode, the use of a different wavelength (1070 nm instead of 355 nm) and the use of different energy values (0.19-1 mJ on a beam diameter at focusing point of 80 μm, instead of 1-5 μJ on 11 μm) caused difference in the interaction mechanisms. More in detail, at high Le values (0.6 J/mm), the depth rapidly drops for increasing pulse energy after a Pe > 0.28 mJ (or equivalently a pulse power > 8 kW), in agreement to what observed by Wlodarczyk et al.…”

“…It can be concluded that the mechanisms involved in the mark formation, as well as the contrast, are more complex than those suggested in [35][36] and a higher number of parameters must be taken into account, as also suggested by several authors [19][20][21] . So, in order to analyse the effect of the process parameters on the mark geometrical characteristics, statistical analysis (ANoVA and RSM) was performed.…”

“…Wlodarczyk et al [35,36] have studied the effect of pulse energy and number of pulses during the laser marking on different metals (included Inconel 625 and Inconel 718) by way of a 10W Q-switched UV nanosecond laser. The marks were obtained by delivering a pre-defined number of laser pulses (one or more) onto a fixed target, varying the pulse en- ergy in the range 1-5 μJ.…”

Предпороговые Эффекты При Воздействии Ультрафиолетовых Лазерных Импульсов На Медь И Ее Сплавы

“…Интересным решением, нашедшим применение в лазерной маркировке металлов, является воздействие на поверхность металла сфокусированным наносекундным излучением [13]. В этой работе маркировка осуществлялась лазерными пятнами с выраженным кратерообразованием.…”

Femtosecond laser writing of nonlinear waveguides in Gorilla® Glass and L-threonine organic crystals

“…Therefore, those materials can be divided in two classes regarding its linear absorption with respect to the pump excitation wavelength. Within the class of opaque materials, specifically for metals, the high spatially selective ablation obtained with fslaser microstructuring have been used, for example, for repairing photolithography masks 6 , hole drilling 7 , production of reflecting computer generated holographic for security [8][9] or beam control [10][11] , maskless alternative fabrication of interdigitated electrodes for faster prototyping 12 , nanoparticles generation 13 and producing superhydrphobic surfaces. 14 Still on non-transparent materials, such as linearly absorbing semiconductors, their surface topography and properties have also been modified by ultrashort pulses.…”