7th UKP Workshop Ultrafast Laser Technology

From April 26 to 27, the community of developers and users of ultrashort pulse (USP) lasers met in Aachen for the 7th USP Workshop. In addition to specialist knowledge, this time it was also about shared memories, because
The workshop is also a family reunion, and the "family" is growing and thriving: there were a pleasing number of young faces among the 150 or so participants.

The workshop provided information on the basics of USP technology and gave an overview of current developments in the field of USP beam sources and the necessary system technology. The focus was on individual beam shaping solutions optimized for specific processes. The latest laser-based applications and processes were presented, which extend the limits of previous technologies in terms of process speed, quality, precision and material bandwidth. The range of applications extended from electronics to energy storage, glass processing and microelectronics. Selected presentations are briefly presented below:

The modulated laser beam for the perfect process

Ultra-short pulsed lasers are versatile in laser material processing. They work even more efficiently if the laser pulses are optimally manipulated in space and time. The importance of this for the new high-power sources with 300 W and more was demonstrated at the "7th UKP Workshop Ultrafast Laser Technology" in Aachen. It was also possible to see how UKP lasers make the electrodes of batteries for electric cars or hydrogen systems significantly more efficient.

Secondary sources are on the rise

Secondary sources are beam sources in which high-intensity laser radiation is transferred to other spectral ranges that are often far removed from the laser wavelength. This can be special X-ray radiation, but electron and even proton beams are also being discussed.

To date, the laser and machine manufacturer Trumpf in particular has pioneered this field with the Extreme Ultra Violet (EUV) source for the company ASML. However, as extremely powerful lasers are required for secondary sources, no one has really believed in their market relevance until now. Dr. Torsten Mans, Product Manager Secondary Sources at Trumpf, changed that with his presentation. The company is apparently bringing together expertise from different areas in order to achieve intensities up to the terawatt range with diode-pumped high-repetition USP lasers. Mans sees initial applications in metrology in the semiconductor sector. If large accelerators can be successfully replaced as beam sources, complex test procedures could move from research to production or new therapies in the healthcare sector could become possible.

The participants of the workshop were welcomed at the event location "Das Liebig" in Aachen

Beam modulation in space and time increases productivity

What happens when pulsed laser radiation marks a curve on the workpiece during processing? It slows down, the distance between the pulses is reduced and the contour becomes thicker. Laser manufacturer Amplitude has tackled this problem and offers a single-pulse control system that can, for example, regulate the distance between individual pulses in a contour. Whether GHz bursts, single pulses or adjustable pulse sequence frequencies - flexible control of the pulse sequence is becoming the standard for USP lasers. This allows processes to be designed for maximum productivity.

What happens when pulsed laser radiation marks a curve on the workpiece during processing?

The situation is similar with spatial modulation, and several exciting innovations in this field were presented in Aachen. The first was presented by Gwenn Pallier from the French company Cailabs: Repeated reflection on a phase plate (Multiplane Light Conversion MPLC) is used to manipulate laser pulses in such a way that, for example, higher modes are suppressed and depth of field is improved. Professor Carlo Holly from RWTH Aachen University demonstrated something similar. He uses artificial intelligence in optical design. To do this, Holly uses two diffractive optical elements that are connected in series to manipulate the propagation of the laser beam in three dimensions. This not only gives him special beam profiles, but also significantly increases the depth of field.

Whether hydrogen electrodes or OLED displays - productivity is the key

Professor Arnold Gillner, co-organizer of the workshop, summarized at the beginning of the conference what has been achieved in the field of industrial USP lasers. At the top of the list of applications is the functionalization of surfaces. USP lasers can increase the surface area of electrodes and thus significantly improve the efficiency of both batteries and hydrogen electrodes. "The areas that need to be processed are in the order of square kilometers," said Gillner, describing the demand for this application.

For years now, USP lasers have played a major role in the manufacture of smartphones. Dr. Stefan Janssen provided examples of this from his work at LG-Electronics PRI in Korea. One exciting detail was the imaging optics for processing polymer OLEDs: weighing in at 24 kg, they are unusually large, but allow for more productive processes. Janssen describes the next steps as the potential of energy-modulated fs bursts and the regulation of pulse intervals in free-form contours during glass processing. Process control and predictive maintenance are also exciting topics for him - as is so often the case with 24/7 production.

Higher productivity was also the focus of the presentation by Dr. Stephan Eifel from Pulsar Photonics. In addition to standard machines, the company specializes in special machines with multi-beam optics to make more out of a single USP laser. Eifel sees a trend towards higher ablation volumes per component: "We're talking about volumes in the region of 10,000 mm³ and more." The availability of more powerful laser sources and modulators for the beams is good news for him. "Now the machines have to cope with long processing times." He plans 100 hours or more for one component. That's how long the machines have to run reliably and stably for large components.

Parallelization is the way to greater productivity. Splitting one beam into several, each of which then applies partial beams to the workpiece via several scanners and other multi-beam optics - this is how it is implemented in the machines at Pulsar Photonics. In the example shown, there are 24 beams in parallel on the workpiece at a feed rate of more than 1 m/s. More speed is certainly desirable. Production is monitored with 100 measurements per second. The biggest challenge at the moment is real-time data processing.

Two virtual lab tours

In addition to the presentations and the many opportunities for personal discussions, an important part of the workshop was the digital tours of Fraunhofer ILT laboratories. During the pandemic, this was only possible via live broadcast. This was adopted for the 7th UKP workshop, as the virtual tour eliminated the need to travel to the institute and the camera was able to capture perspectives that would be difficult for normal visitors to reach. The first visit was to the BatteryLab. Research on laser-based production processes for battery manufacturing has been conducted there since 2020. "It is crucial to keep an eye on the entire production chain," says Reininghaus, describing the strategy. The various steps along the production chain are being researched, with the focus on increasing productivity in all steps.

Increased productivity was also the focus of the second lab tour. A new multi-beam UV laser system was presented there. It uses 64 individually modulated partial beams, as Martin Osbild explained on site. The 4 x 5 m system will undergo extensive testing until June 2023 and will then be used as an application laboratory for customers and partners of Fraunhofer ILT.

Photos: Fraunhofer ILT, Aachen