Speaker
Description
Laser interaction with near-critical density plasma generated from low-density polymer foams provides an efficient platform for direct laser acceleration of electrons. In experiments performed at the sub-picosecond PHELIX laser facility, polymer foams with densities ranging from 2 to 8 mg/cc were homogenized using a controlled nanosecond pre-pulse to ensure entire plasma homogenization before being irradiated by a relativistic short-pulse laser at intensities of approximately 1E19 W/cm2. This interaction drives high-current electron beams with energies up to 100 MeV through direct laser acceleration [1, 2]. When directed onto high-Z converters such as gold or tungsten, these relativistic electrons produce ultra-bright, high-intensity bremsstrahlung radiation in the MeV range [2-5].
Recent campaigns demonstrated record-breaking laser-to-photon conversion efficiencies of up to 1.8 % for photon energies above the giant dipole resonance threshold. To characterize these primary and secondary radiation sources, advanced nuclear diagnostic methods were implemented, including sample activation followed by high-purity germanium detector spectroscopy to analyze photonuclear reactions in tantalum, gold, and indium. These techniques enable precise evaluation of bremsstrahlung spectra, effective photon temperatures, and secondary neutron fields even under challenging high-gamma-background conditions. The developed platform demonstrates great potential for driving diverse nuclear reactions and establishing advanced radiation-based diagnostics for high energy density science and plasma physics at modern laser facilities. Our approach was confirmed during shots at the NIF-ARC facility in Feb. 2026, providing ten times higher 196Au yield per J laser energy compared to application of compound parabolic concentrator (CPC) [6].
[1] A. Pukhov, Z.-M. Sheng, J. Meyer-ter-Vehn (1999), Particle acceleration in relativistic laser channels. Physics of Plasmas, 6, 2847-2854.
[2] O. Rosmej, et al. (2020) "High-current laser-driven beams of relativistic electrons for high energy density research." Plasma Physics and Controlled Fusion, 62.11, 115024.
[3] P. Tavana (2020) Untersuchung photonuklearer Reaktionen in relativistischen Laser-Materie-Wechselwirkungen am PHELIX-Lasersystem. Master's thesis. Goethe-Universität Frankfurt, Germany.
[4] M. Günther (2011), Untersuchung relativistischer Laserplasmen mittels nukleardiagnostischer Verfahren. Ph.D. thesis, Technische Universität Darmstadt.
[5] S. Busch (2024) Anwendung der Nukleardiagnostik zur Charakterisierung von MeV-Bremsstrahlung in Experimenten zur Wechselwirkung relativistischer Laserpulse mit Schäumen. Master's thesis. Goethe-Universität Frankfurt, Germany.
[6] S. Kerr (2023) Phys. Plasmas, 30, 013101.