What makes these markings so unique?
Gehrmann: They have an approximate slit spacing that is related to the laser wavelength. The resulting pattern is as unique as a fingerprint. This also depends on the grain size of the raw material and whether there are any imperfections for example. This is why you cannot counterfeit an individual marking even if you use the same laser system. Having said that, the challenge is to read the marking. There is still some room for improvement in this area.
How so?
Gehrmann: From the outside, the onlooker notices the holographic effect as an obvious security feature. Yet if a manufacturer wants to be 100 percent certain, they have to read the microstructures – first, right after the marking to record and save it and once again for recourse purposes to verify it. In actuality, the marking would have to be read for each individual component. And although this would be quite an elaborate process, it could be justified when it comes to safety-related components. Meanwhile, in the case of polymers, you could mark an injection mold to be able to, later on, identify the tools that were used to cast each component.
The readout is possible via a high-resolution optical microscope or laser scanning microscope. Another option is a scanning electron microscope. However, this process would be elaborate and expensive.
What pros and cons do you see in the ultrashort pulse laser marking process compared to other marking techniques?
Gehrmann: One drawback is the price. Even though laser source costs continue to fall, the marking technique with USP laser is still about ten times more expensive than nanosecond laser marking.
The higher resolution of USP lasers is clearly a major advantage because it allows us to produce more refined structures. What’s more, the marking features a higher contrast and durability. It also facilitates diffractive structures, meaning holographic effects on surfaces, but that is not an essential factor.