High-power diode laser stacks with high duty cycle: Key components for pulsed laser technology

A new generation of laser applications is currently emerging, based on pulsed solid-state lasers of the highest energy class. These systems produce ultrashort optical pulses with energies in the megawatt to petawatt range, that are used to generate a wide variety of forms of radiation. This enables applications in material processing, spectroscopy and imaging that cannot be realized with any other technology. Pump sources based on stacked arrays of diode lasers (so-called stacks) are an essential enabling component for these novel laser systems.

In the HOTSTACK project, coordinated by Trumpf GmbH, we are addressing this need through research into significantly improved diode laser and assembly technologies. We will realize two types of high-power diode laser stacks, as research prototypes. The development focus is on increasing both the repetition rate and the energy of the optical pulses; as well as ensuring a more cost-effective fabrication process for the stacks.

The development of “Type 1” stacks (industrial design) is aimed at the emerging secondary source industry and will realize an especially cost-effective and well-developed industrial design. Specifically, project partner TRUMPF targets increasing the average pump power per stack by a factor of around 20 compared to current systems, via higher pulse repetition frequency and the higher optical pulse power. Parallel research efforts by project partner Finetech into new die bonding technologies and production automation should also drastically reduce manufacturing costs.

In addition, “Type 2” stacks (research design) will be developed, supporting research into the next generation of innovative laser systems of the highest energy, for example the forthcoming EuPRAXIA facility. The aim is to increase the average pump power by a factor of 100. The work on this will mainly take place at the Ferdinand-Braun-Institut.

Diode laser are needed in high volumes for high-energy-class laser systems, but are produced using complex manufacturing processes such as epitaxial growth, III-V wafer structuring and etching processes, and reliable process control is essential for understanding and controlling the manufacturing process. Therefore, project partner LayTec (in cooperation with the FBH) will develop innovative integrated optical analysis techniques for both III-V epitaxial growth and wafer process technology, that are intended to improve process understanding and control for such structures. The innovative control methods target greatly increased diode laser fabrication yield, and hence are anticipated to directly enable a highly-cost-effective diode laser fabrication, as needed to support large high energy laser systems.

HOTSTACK is a "ProFIT Innovation" project and is co-financed from 2023 - 2025 with funds from the European Fund for Regional Development (ERDF) Berlin.