Novel ultrashort-pulsed lasers and laser sources for industrial applications

Scaling picosecond and femtosecond laser sources and process technology to 10 kW and beyond.

Having found early wide-scale use in mobile device glass scribing applications, ultrashort-pulse (USP) lasers in the picosecond (ps) or even femtosecond (fs) range have been available for more than a decade. The ability to process numerous materials with micron precision - without splatter or thermal side effects - promises to expand the range of potential applications for industrial USP lasers. However, USP laser use in applications that require high repetition rates and high power to achieve economically viable throughput has been limited.

The problem is that while a few USP laser sources on the market may exceed 150 W or 150 µJ per pulse, most deliver less. Even if stronger sources were available, using the additional power is a challenge because ultrashort pulses lose their “cold ablation” capability when too many of them are focused into one spot.

Understanding this challenge, the German Fraunhofer-Gesellschaft has identified USP laser systems as a great opportunity and put together the expertise of not less than 13 of its institutes to develop a new generation of such systems. The Fraunhofer Cluster of Excellence Advanced Photon Sources (CAPS) plans to not only overcome USP laser power limitations, but also develop technologies along the process chain from pulse generation to process technology, and real-world applications.

Upscaling to kilowatt power

One of the upcoming challenges for the CAPS cooperation partners is the conversion of power into throughput, which will require a new process technology for USP laser systems, which starts with basic research on laser matter interaction at high repetition rates and high pulse energies. Another challenge is power distribution: one concept for pulses with higher energy involves splitting the beam into many parallel beamlets. Another approach involves building acousto-optical modulators into the beamlets, yielding a kind of laser matrix printer that can be realized by switching single beamlets on and off. In a third and extremely flexible version, the beamlets can be sent through a liquid crystal modulator that can generate almost any pattern or beam properties from the original beam.

The fiber and slab concept

One key to creating high-power ultrashort laser pulses is finding the right amplification scheme.CAPS project researchers will implement two proven concepts with very specific advancements that will enable substantial progress towards 10 kW average power. One is based on coherently coupled fiber amplifiers and has already delivered promising results: in recent tests, it delivered an average power of 8.9 kW in single-mode radiation with a beam quality M² <1.2.

Besides, an Innoslab amplifier is used, which uses specific diode-pumped slabs and is currently designed for 2 kW output from a single amplifier. For the next two years, the plan is to scale the system up to 5 kW output using two amplifiers and finally, the goal will be doubling this to 10 kW using a disk-based power amplifier stage. In parallel to the laser sources, beam delivery technology is developed to make effective use of the radiation.

Application development

As mentioned earlier, the sources will be further developed in parallel to the development of appropriate process technology. The application labs offer several beam sources, extensive diagnostics, and an increasing set of beam delivery technologies. Most of the 13 partners in the CAPS collaboration are working on applications of these new USP laser sources.

Fraunhofer-Cluster of Excellence Advanced Photon Sources CAPS

CAPS, currently with its 13 partner institutions, embarks on developing a new generation of high-average-power USP laser systems. The collaboration uses two application labs with fiber- and slab-based amplifiers producing several kilowatts of subpicosecond laser pulses. In parallel to the laser sources, the beam delivery technology is developed to make effective use of the enormous performance characteristics. While the partners develop a range of new technologies, their ambition is actually to make the USP laser a tool with average powers of current CW fiber lasers plus the unique features of USP lasers, including high precision and low or no dependency from the processed material. The CAPS user facility is also open for testing and demonstration of new applications from industry.

For more information and contacts on the CAPS, please visit www.caps.fraunhofer.de

CAPS at the Photonics West

The novel CAPS laser sources will be presented in various lectures by our colleagues at the LASE conference at Photonics West in San Francisco:

February 3rd, 2020 | 1:30 – 2:00 pm

Michael Müller (Institute for Applied Physics, FSU Jena)

7.2-kW ultrafast fiber laser based on coherent combination

Session: Coherent Combination of Fiber Lasers

February 4th, 2020 | 3:30 – 4:00 pm

Martin Gebhardt (Institute for Applied Physics, FSU Jena)

Soft x-ray high order harmonic generation driven by high repetition rate ultrafast thulium-doped fiber lasers

Session: Thulium Doped Fiber Lasers and Amplifiers II

February 5th, 2020 | 11:10 – 11:30 am

Christoph Stihler

The sensitivity of the mode instability threshold to different types of intensity noise

Session: Mode Instability/Stimulated Thermal Rayleigh Scattering

Further information about trade show of the Fraunhofer IOF at Photonics West can be found at:
https://www.iof.fraunhofer.de/en/pressrelease/2020/photonics-west.html