With the demand of global electricity expected to double by 2045, fusion energy is gaining strategic importance as a sustainable, carbon-free power source. Among the various approaches, laser-driven inertial fusion has recently attracted increasing attention — not only in science, but also in politics and industry. In Germany, this interest sparked action, with the release of the national funding program Fusion 2040 by the Federal Ministry of Education and Research (BMBF) in late 2023. This program is the result of a consultation process that commenced in 2022. In addition to expert panels and stakeholder workshops, this comprehensive process led to the formation of the BMBF commission on inertial fusion energy (IFE), chaired by Constantin Haefner. Courtesy of iStock.com/fotojog. Fusion 2040 marks a significant turning point in Germany’s fusion strategy, supporting magnetic and laser-based fusion pathways for the first time. It enhances ongoing world-class basic science research with additional funding of more than €400 million that will be put toward technological developments needed for the first fusion power plant. This will bring Germany’s investment to more than €1 billion over the next five years, which does not account for the funds brought in from Europe and the ITER project. Fusion 2040 draws on expertise from universities, industry, and key organizations such as the Fraunhofer-Gesellschaft, Max Planck Institutes, and Helmholtz Centers to cultivate a national innovation ecosystem that bridges research and industry. Importantly, the program is technology-agnostic, which is necessary to support IFE and magnetic fusion energy. Today, Germany excels in basic research and essential technologies related to magnetic confinement, fusion materials, and the fuel cycle. What it currently lacks is foundational research in inertial confinement fusion, which is the basis for IFE. But Germany’s laser and optics industry, as well as German-led applied research in these areas, make it a world leader in the supply of enabling technologies for inertial fusion. Two world-leading experts from Germany, Constantin Haefner and Andreas Tünnermann, are uniquely equipped to offer insights into this dynamic. Haefner, an internationally recognized expert in IFE and high-energy lasers, is an executive board member of Fraunhofer-Gesellschaft, responsible for research and transfer. He is former director of the Fraunhofer Institute for Laser Technology ILT, a world-leading institute for the development of laser technology and applications, and former program director at Lawrence Livermore National Laboratory. Tünnermann is director of the Fraunhofer Institute for Applied Optics and Precision Engineering IOF (Fraunhofer IOF). The institute is acclaimed for its high-end optics R&D and high-power fiber laser systems. Constantin Haefner. Courtesy of Fraunhofer/Markus Jürgens. Andreas Tünnermann. Courtesy of Anna Schroll. Haefner and Tünnermann shared their insights with Photonics Spectra contributing editor Andreas Thoss. Lasers playing a pivotal role in IFE and magnetic fusion energy Thoss: As a leading expert in IFE and head of the German Expert Commission on IFE, can you share your insights on the current state of the field? Haefner: IFE holds incredible promise for the future of energy production, a real transformative shift in power generation. With fusion energy, the cost of energy will be mostly determined by the cost of a power plant and its operations, while the fuel is cheap and abundant. The achievement of igniting a self-sustaining burning plasma at the National Ignition Facility in December 2022 marked a groundbreaking milestone, sparking excitement across the global scientific community. The National Ignition Facility — the only fusion ignition-capable infrastructure worldwide — has since repeated this experiment numerous times, consistently improving yield and energy gain, demonstrating a robust physics platform, and deepening our understanding of the fusion process. This success provides a first step on the long journey toward harnessing the immense energy produced by fusion, potentially offering a clean energy source. Fusion ignition also initiated a global competition among nations. Beyond its green energy character, countries recognize that fusion can unlock market oppor- tunities for technologies and redefine energy security and energy sovereignty for societies. For Germany, fusion energy represents a unique opportunity to lead in the fusion landscape, particularly for its robust high-precision laser and optics industry. Many optical and laser components deployed in inertial confinement fusion/IFE research facilities today were produced or invented in Germany, and its industry is well positioned to furnish a significant part of the supply chain for a fusion demonstrator. Lasers also play a role in reactor designs, including those for magnetic fusion energy. Lasers and optical technologies provide important plasma diagnostic capabilities; laser-based processes enhance surface properties of fusion materials, improving resistance to erosion and damage or providing specific functions. Techniques such as laser welding and cutting enable the precise assembly of reactor components, while laser-based additive manufacturing allows for the creation of complex geometries, including the use of advanced materials. Thoss: You recently joined the board of Fraunhofer and are responsible for research and technology transfer for the entire Fraunhofer society. What are the greatest challenges in bringing fusion to the grid? And what role will Fraunhofer play here? Haefner: The leap from fusion experiments to commercially viable power plants demands significant breakthroughs in technological developments. Many are needed, from efficient, industrial-grade high-energy lasers to robust optics that survive the harsh conditions close to a fusion reactor, to closing the fuel cycle and harvesting the energy from the fusion reactions. The world is far from being able to build a power plant tomorrow, and this includes all technological approaches; many needed technologies and supply chains are at the conceptual level at best. The mission of Germany’s Fusion 2040 program is to develop these technologies, and Fraunhofer is integral to this effort. Our focus on applied research aims to close critical gaps while facilitating technology transfer to cultivate a competent and competitive industry. Fraunhofer is poised to establish robust supply chains for the high-quality components and materials that are vital for fusion reactors, leveraging our extensive competencies across 75 institutes and our strong network in industry. The largest challenge toward realizing fusion energy is to get going, close science gaps, and build a robust supply chain. If the world is to achieve its first fusion power plant by 2050, we must advance R&D in parallel and foster international collaboration. This approach presents several challenges, such as the need to strategically align our efforts, prioritize low-risk approaches while phasing out less promising alternatives, focus our investments wisely, and establish international open research infrastructures for testing physics, innovative ideas, and components. A significant gap in R&D exists in the moderate-scale demonstration of fuel breeding blankets, coupled with efficient tritium extraction while simultaneously generating energy for thermoelectric conversion. This shortfall poses a critical challenge for advancing fusion technology, as there is currently no testing facility worldwide — referred to as a volumetric neutron source — that can facilitate this essential research. This is just one example, but many other modern technologies have undergone similar challenges, and I am positive that these will be resolved with increasing speed. Last, we must establish a collaborative [intellectual property] strategy among all contributors that effectively protects and leverages innovations for a strong return on investment. This strategy should also guarantee that all participants have equitable access to licensing opportunities, allowing them to benefit from the resulting innovations and providing collective impact for driving the advancement of fusion energy. Thoss: Your Memorandum of IFE (2023) called for establishing an innovation ecosystem in fusion energy and provided recommendations for actions. How far have we come toward those achievements — and what effect will fusion energy have for Germany? Haefner: Germany has made tremendous strides in advancing its fusion energy initiatives, establishing a comprehensive fusion strategy through the IFE Memorandum in 2022 and launching the public-private partnership program Fusion 2040 in 2023. The first call of Fusion 2040 was oversubscribed by 3×, highlighting the enormous interest from industry and its eagerness to invest in maintaining and enhancing its competitive edge in the fusion technology sector. In addition, Germany’s Federal Agency for Disruptive Innovation (SPRIND) invested approximately $100 million in technology procurement and development to support its startups. And several State governments have launched supporting programs, ranging from substantial investments into education and training of next-generation talent, funding some experimental infrastructure, to supporting their startups with seed funding. Germany has also launched a project aimed at evaluating and developing recommendations for a comprehensive regulatory framework for fusion research, ensuring a conducive environment for innovation and safety. This is of utmost importance to reassure industry in clear and sustained rules for engaging in fusion technology development and encouraging international investors in actively participating in building our fusion ecosystem. By its prompt actions, its competence and capabilities in plasma physics, tokamak and stellarator technologies, fuel cycle and materials science, and the swift launch of the Fusion 2040 program, the German government has propelled the country to the forefront of global fusion energy initiatives. These efforts not only position Germany as a leader in the development of sustainable energy solutions but also attract significant interest and investment from both domestic and international stakeholders. Pushing optical frontiers for fusion As director of the Fraunhofer IOF in Jena, Germany, Tünnermann holds a critical position, spearheading development of the optical components and systems upon which laser fusion will depend. Funded by the German BMBF, the teams at Fraunhofer IOF work on several projects with partners from research institutes and industry to develop the necessary manufacturing technologies and components. Tünnermann discusses Germany’s optical heritage, the role of Fraunhofer in building a fusion ecosystem — and why working on fusion is like making shovels for a gold rush. The journey is uncertain, but the tools created will have a far-reaching influence. Thoss: What do you think when you hear the term “laser fusion”? Tünnermann: Big challenge, big chances. The promise of clean energy generation is one of the rare cases where the work of physicists makes it to the evening news. So, we have a chance to tell people what science can do to save our planet. That is really unique. On the other hand, we have to explain how long it will take to fulfill such a promise. Laser fusion research has made exciting progress in recent years, but we are currently facing a typical research problem: An experiment that has worked well a few times in the lab is not a technical solution ready for continuous operation 24/7. It takes a lot of work by scientists, engineers, and many other experts to build a power plant that has never been built before. Thoss: What is your part in making laser fusion happen? Tünnermann: There is just one place in the world where laser fusion was successfully executed — the National Ignition Facility in California. That was a huge achievement, but it was made at a dedicated research facility. I think most experts agree that a fusion power plant that operates around the clock places much higher requirements on its optics. This is a huge challenge that we are picking up. Here at Fraunhofer IOF, teams have been gathering know-how for decades to develop optical components, systems, and processes for 24/7 operation in industrial facilities. And this is what we bring in to develop optical components and processes for laser fusion. With the Fusion 2040 program from the German government, we are receiving funding for a number of projects to develop components and processes for future fusion systems. Thoss: Can you provide some examples of what you are working on? Tünnermann: One example is laser mirrors. You know, modern optics has long had a home here in Jena. The first dielectric antireflection coatings were introduced here by Schott almost 100 years ago. Even if optics is supposedly an old technology, there are always new, surprising challenges. This also applies to mirrors. Extreme-ultraviolet mirrors are a prominent example. But even seemingly simple laser mirrors are still challenging. We are now working on the Scalable Highpower Reflectors for Petawatts (SHARP) project, which is funded by the German BMBF. Together with seven industrial partners and two other research institutes, we aim to develop a new generation of highly reflective laser mirrors that will meet the extreme requirements of future petawatt laser fusion reactors. Thoss: How far will you go in this project? Tünnermann: The project team is made up of various champions along the value chain, so we will investigate the scientific and technical fundamentals to develop novel manufacturing technologies for super-polished, curved, large-area optics, and move forward, step by step, along the precision optics value chain. It all starts with the substrate material and the manufacturing process. An important topic is a defect-free substrate surface. We are developing polishing process technologies minimizing subsurface defects, which have been identified to be critical concerning the laser damage. Optics for high average-power lasers will need cooling, so we must find solutions for thermal stabilization and active cooling, novel integrated cooling structures in glass substrates, and to balance thermomechanical effects. This is a huge effort. In the end, we will be developing an entirely new generation of optics that can withstand the enormous loads over an extended period of time. Just imagine what it takes, going from one shot per day up to 15 shots per second. Thoss: Isn’t coatings considered a separate topic? Tünnermann: Yes and no. Coatings are part of the system, so we have to think about it together with the project partners. But we also have a separate project where we are working on completely new coatings based on a combination of antireflective coatings and nanostructures. It is called nanoAR and we are one of nine collaborating partners working on this idea. We are pursuing two different approaches here. One relies on nanostructured or nanoporous antireflective coatings based on high-bandgap materials to provide the required laser damage threshold. Another approach is to directly nanostructure the optical surface. There will be no coating, just nanostructures. Thoss: It is obvious that such technologies have more potential than fusion. What do you have in mind? Tünnermann: The general idea behind these projects is actually quite compelling: Take some excellent players in the field, let them work on a challenging technology for a distant project, and let them profit from the new technology right after the project finishes. It is a bit like making the shovels for a gold rush; we do not know yet who will benefit from fusion energy and when — but making better optics will have an immediate impact on many industries. A researcher holds a highly reflective mirror for laser applications. The technology is to be optimized for laser fusion. Courtesy of Fraunhofer IOF. First and foremost, laser materials processing could benefit. We see an insatiable appetite for more power, leading to a steady demand for ever better optical coatings. In particular, the advent of ultrashort-pulse lasers will benefit from these coatings. Other benefited areas could be laser systems for which maintenance is difficult, such as space applications or, again, extreme-ultraviolet generation. The combination of advanced substrates and more durable coatings could be attractive for this multibillion-dollar market. Meet the interviewees Constantin Haefner has been a member of Fraunhofer’s executive board, responsible for research and transfer, since February 2025. After more than 15 years in Silicon Valley, Haefner returned to Germany to take over as director of the Fraunhofer Institute for Laser Technology ILT, one of the world’s leading institutes for the development of laser technology for industry, research, space applications, and medicine. Since 2019, he has been a full professor and holds the Chair for Laser Technology LLT in the Faculty of Mechanical Engineering at RWTH Aachen University. Haefner earned his physics degree from the University of Konstanz in 1999 and his Ph.D. from Heidelberg University in 2003. He has received several awards for his achievements, including OSA (Optica) Fellow (2017), the Federal Laboratory Consortium Tech Transfer Award (2018), and the Fusion Power Associates Leadership Award (2024). Andreas Tünnermann is a German physicist and university lecturer. From 1992 to 1998, he headed the development department of the Laser Zentrum Hannover and habilitated in 1997. In 1998, Tünnermann accepted a professorship at the Friedrich Schiller University Jena as a professor of applied physics and took over the management of the Institute for Applied Physics. Since 2003, he has also been director of the Fraunhofer Institute for Applied Optics and Precision Engineering IOF in Jena, Germany. Tünnermann has received numerous awards for outstanding achievements, including the Gottfried Wilhelm Leibniz Prize in 2005, the ERC Advanced Grant by the European Research Council in 2015, and the Cross of the Order of Merit of the Federal Republic of Germany in 2024.