Multi-pass cells for next generation laser-plasma accelerators

• Applicants: Dr. Christoph Heyl; Professor Dr. Oleg Pronin
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 545612524

For the past decades, intense ultra-short optical fields have been routinely used for a wide range of applications, ranging from probing ultrafast light-matter interactions to generating ultrafast secondary particle and radiation beams. Today’s far-ranging impact of ultrafast lasers, as well as prospective applications, sets challenging demands for key characteristics of tomorrow's ultrafast lasers, including highest peak and average powers, shortest pulse durations, and highest wall-plug-efficiencies. In particular, compact high-flux laser-driven plasma accelerators (LPAs), representing a formidable application of ultrafast lasers, are expected to enable entirely new modalities in medical diagnostics, radiation therapy and industry-scale imaging. While laser-plasma acceleration is well-established in many laboratories, a key obstacle hindering the wide deployment of LPAs is the very low repetition rate. This is because LPA is so far almost entirely based on Titanium-Sapphire laser technology. Strikingly, an ongoing paradigm change in high-power laser technology is now bringing up an entirely new route to tackle this challenge: efficiently post-compressed high-average power Ytterbium (Yb) lasers are emerging as powerful solutions combining highest repetition rates with highest peak powers. In particular, the recent invention of a novel post-compression technique, the multi-pass cell technique, offers tremendous opportunities. This quasi-guiding concept offers many advantages over conventional guiding structures. The method has enabled benchmark results yielding sub-50-fs pulses at average powers exceeding 1 kW, has facilitated femtosecond post-compression at pulse energies above 100 mJ with large compression ratios, and supports few-cycle pulses. Thus, already today, MPCs play a disruptive role in the field of ultrafast optics and beyond. However, the fundamental mechanisms underlying these nonlinear quasi-guiding systems are poorly understood. These considerations raise the following key challenges: Understanding the physics underlying spatio-temporal couplings and temporal pulse characteristics of MPCs. In particular, methods to enable post-compressed TW-class few-cycle pulses with high temporal pulse contrast and excellent spatial beam quality need to be developed. MPC quasi-guiding systems present great energy scaling characteristics. However, energy-scaling methods enabling compact-footprint multi-100 mJ-class post-compression systems need to be demonstrated. Addressing these challenges will require the development of profound theoretical concepts of the underlying physics as well as dedicated numerical and experimental efforts, targeting pulse temporal compression and cleaning as well as efficient energy-scaling. This will enable the ultimate demonstration of high-quality multi-TW laser pulses at kHz repetition rates for next-generation LPA sources with game-changing prospects for highly energetic laser systems in general.

• DFG Programme: Research Grants
• International Connection: France
• Partner Organisation: Agence Nationale de la Recherche / The French National Research Agency
• Cooperation Partners: Louis Daniault, Ph.D.; Dr. Xavier Delen; Dr. Marc Hanna; Dr. Rodrigo Lopez-Martens