[BELLE HISTOIRE] LaserSurf: spotlight on laser surface functionalization

IREPA LASER is a French technology company specializing in industrial laser applications, in particular additive manufacturing, welding and micromachining. It supports players from all industries in these areas, from the definition of their needs to the operational implementation of appropriate solutions in the field.

Since its creation in 1982, the company has always been closely linked to INSA Strasbourg. And with good reason: it was on the premises of ENSAIS - the school's former name - that it was born, under the impetus of one of its students: Olivier Fréneaux. " From then on, the original link between the two entities has only grown stronger," sums up Frédéric Mermet, micro-applications expert at IREPA LASER. " This relationship has, of course, taken the form of research projects, but also training exchanges: we regularly welcome students to our premises to introduce them to industrial laser professions. The ICube laboratory (CNRS/Université de Strasbourg/INSA Strasbourg/ENGEES), part of the Carnot TSN institute, has been a logical part of this long-standing partnership since its creation in 2013.

Surface functionalization inspired by nature

On the research side, the two partners have carried out a number of joint projects, starting with the "photonic jet" technique, which involves focusing a laser beam very finely, beyond the usual limits. This process, for which joint patents have been filed, can be used for a wide range of industrial applications, including microengraving. For example, it can be used to add a tiny marking to an object, ensuring traceability and limiting the risk of counterfeiting.

IREPA LASER and ICube work mainly on femtosecond lasers, characterized by their very short pulse duration, of the order of a few hundred femtoseconds - or millionths of a billionth of a second. Once again, this technology can be used for a wide range of applications: extremely precise cutting, welding, drilling on a very small scale, or even functionalizing glass, metals or semiconductors. Functionalization consists in removing a small volume of material from a surface to create a pattern that imparts new properties to the material without additional chemical deposition: hydrophobicity, friction reduction, antibacterial texture, colored effects without the addition of pigments...

But how can we predict the function induced by the addition of a given motif? " This is an ongoing challenge for industry: we are constantly seeking to improve our understanding of textures and their impact on material properties," explains Frédéric Mermet. " And to do this, we rely heavily on biomimicry, drawing inspiration from nature: for example, the hydrodynamic scales of sharks, the hydrophobic texture of lotus flowers, the anti-reflective surface of the wings of certain insects..."

The challenge of industrial-scale functionalization

While this knowledge has yet to be fully developed, the two partners have already built up expertise in surface texturing over the years. " However, it's not always possible to generalize: from one material to another, the behavior associated with a texture can be very different," warns Sylvain Lecler, professor at INSA Strasbourg's ICube laboratory. " Added to this is a major challenge: for relevant use in industrial environments, we now need to be able to apply our know-how to much larger surfaces, which poses new challenges. "

IREPA LASER and ICube have decided to create a new structure for their collaboration: the LaserSurf joint laboratory. Winner of the LabCom 2022 call for projects issued by the French National Research Agency (ANR), the joint laboratory was launched in February 2023, for a period of four and a half years. " The joint laboratory offers us greater coherence: until now, research projects were carried out independently, whereas from now on, they are part of a long-term logic ", Sylvain Lecler is delighted to report. " This multi-year projection also helps us to explore subjects further upstream, to check whether they are of interest to IREPA LASER.

LaserSurf employs around 15 permanent staff, plus PhD students, post-docs and interns. In addition, two engineers have been recruited as part of an inter-Carnot project involving the Carnot institutes TSN and MICA. The Carnot TSN institute has extended its support to the joint laboratory by backing the production of a video presenting LaserSurf.

Laser control and shaping

Within the framework of this new structure, the two partners intend to build on their knowledge of femtosecond lasers and support the scaling-up of the technology. Their sights are set on applications such as airplane wings functionalized by laser texturing to reduce air resistance, and hence the aircraft's energy consumption. " Nevertheless, such an ambition implies improving the ability to scan large surfaces with a femtosecond laser, while maintaining the quality and precision of the process," notes Frédéric Mermet. " We therefore need new instrumentation to help position the laser finely in relation to the part, at the right angle. "

One research project in particular is aimed at developing an assistance solution for driving a cobot - a collaborative robot - comprising instruments, sensors and software architecture. The aim is to identify and develop the interface best suited to the control of a femtosecond laser in an industrial environment, meeting the requirements of precision and speed of data flow for real-time control. A first version of the tool has already been developed and successfully tested, with encouraging results that the research team intends to continually improve.

Another obstacle to the use of femtosecond laser processes by industry is their current cost. LaserSurf therefore intends to make them more accessible, in particular by improving their efficiency. " To achieve this, we can act on both the spatial and temporal shaping of the laser," explains Sylvain Lecler. "It can, for example, be made up of a matrix of points, each of which can have a particular shape. As for the temporal aspect, we can use high-frequency bursts, which modify the interaction between the laser and the material.

Monitoring the laser texturing process using AI

In parallel, researchers have developed an artificial intelligence algorithm to monitor the progress of a laser texturing process. More specifically, this involves analyzing the light emitted during the operation, using a spectrometer. " The AI's role here is twofold," describes Sylvain Lecler. " Firstly, based on its learning data, it is able to check whether the parameters requested from the laser are indeed those applied to the part. For example, it provides a measure of fluence - the density of laser energy. Our model then learns, from a set of training data, to establish a correspondence between laser parameters and the color effects generated. This now enables it to predict the color that will be obtained by texturing based on the parameters used. "

Although the tracking algorithm is already operational, it still needs to be perfected, in particular by increasing the frequency of measurements. In addition, the LaserSurf team, which has so far concentrated on the question of color effects, would like to adapt the model to other functionalities.

As a result, IREPA LASER and ICube are conducting multiple research projects simultaneously, with the aim of producing major innovations by September 2027, when the joint laboratory is due to come to an end. " But, of course, our collaboration will not cease at that point," Sylvain Lecler projects. " It began over forty years ago, but there's still so much to discover that it's not about to end! We plan to keep LaserSurf going, even after the ANR funding comes to an end. " To continue exploring the infinite possibilities of industrial lasers.