Speaker
Description
Relativistic laser-plasma driven high energy (MeV) photon and particle generation is an attractive basis for many applications, but still a challenging and not well understood topic within the laser-plasma physics. The relativistic laser-matter interaction was more than two decades investigated in the framework of different aspects of laser-plasma creation. One of these is the generation of photons with MeV energies [1,4,5] as well as the relativistic acceleration of electrons [2] and ions [3]. MeV-gamma radiation can be in general produced by two ways. Laser ion acceleration has been investigated over the last two decades and different acceleration mechanisms identified. These acceleration mechanisms depending on laser pulse parameter and target systems. The most widely investigated mechanism is the target normal sheath acceleration (TNSA), which based on interaction of relativistic laser pulse with µm thick solid target systems [6-8]. Other mechanisms are the radiation pressure concepts [9,10], the acceleration in the relativistic transparency regime [11] as well as the breakout afterburner (BOA) concept [12]. Latter mentioned mechanisms based on ultra-relativistic PW-class laser pulses with ultra-high contrast interacting with several nm thin foil targets.
Such sources provide the basis for the generation of neutrons via nuclear reactions. Furthermore, they open the opportunity of laser based nuclear physics. Optimization and control of such sources are promising to path the way towards compactness and high applicability in multidisciplinary science fields [13]. In the past different concepts are discussed for laser-driven neutron sources and for what they are interesting [14-17]. Besides applications of laser generated fast neutrons, the more sophisticated applications are those using neutrons in the energy range below several hundred of keV. Such applications are based in the whole nuclear physics, which need mostly low energy neutrons (tens of eV up to below of 1 MeV) for capture reactions, fission and elastic/inelastic nuclear reactions. Current conventional neutron sources are based on nuclear fission reactors and accelerators. They provide reliable neutron radiation. Especially in nuclear astrophysics and medical applications it would be more suitable to have spatially compact, ultra-short pulsed and ultra-high flux neutron sources most in the epithermal energy range. Therefore, important values are the angle fluence and the conversion efficiency of primary energy to neutrons. A promising basis for such neutron source properties are laser-driven sources. In the past, records were reached in the laser-driven neutron generation, producing means of fast neutrons above more than 10 MeV energies. Such sources where recently used to demonstrate the applicability in material sciences [18]. However, for applications ultra-fast neutrons must be moderated, which lowers the angle fluence as well as the neutron density and decreases the neutron flux.
Recently we demonstrated that there is an applicable potential to generate high efficiency neutrons with energies needed for the above-mentioned applications in nuclear physics [13]. This reached neutrons are in the energy range, represents a best start point to produce high fluence neutrons in the epithermal energy range.
Therefore, in this presentation, we report on recent results with new record values in efficient laser-driven neutron generation for nuclear physics and their applications. The principal approach based on the interaction of sub-picosecond laser pulses in the moderate relativistic laser intensity range with homogeneous sub-mm long-scaled near critical electron density plasmas from low-density foam taget systems [19]. We observed for the first time in such laser pulse interaction with foam-foil target systems the acceleration of highly collimated protons with $dN/dE$∝$E^{-1}$ power law like spectral properties and strongly enhanced maximum cutoff energies with proton fluences of around 10$^{12}$ (MeV sr)$^{-1}$ protons from above 7 MeV up to maximum proton cutoff energy. Furthermore, using foam-high-Z material target systems, we observed strong directed gamma beams with fluences of more than 10$^{12}$ sr$^{-1}$ and conversion efficiency of 2 % above 10 MeV photon energy. Such beams have shown a high capability to provide applicable laser-driven neutron sources in secondary beam-matter interactions. These new findings allow to efficient generate neutrons with ultra-high fluxes and high angle fluences suitable for applications as mentioned above [13]. In laser pulse foam target system interactions at 10$^{19}$ W/cm$^{2}$ intensities of sub-ps pulses, we observed ultra-high fluences of neutrons with more than 10$^{11}$ neutrons per shot with high laser energy to neutron conversion efficiency [13]. These recent experimental and theoretical results have shown promising generation of neutrons for suitable use in nuclear physics and life science applications, which is also discussed in this presentation.
References
1. P.A. Norreys et al., Phys.Plasmas 6, 2150 (1999)
2. S.P.D. Mangles et al., Nature 431, 535 (2004)
3. H. Daido et al., Rep. Prog. Phys. 75, 056401 (2012)
4. C. Yu et al., Sci. Rep. 6, 29518 (2016)
5. P.A. Norreys et al., Phys. Plasmas 6,2150 (1999)
6. S Hatchett, et al., Phys. Plasmas 7, 2076 (2000)
7. R. Snavely et al., Phys. Rev. Lett. 85, 2945 (2000)
8. M. Borghesi, NIM A 740, 6_9 (2014)
9. T. Esirkepov et al., Phys. Rev. Lett. 92, 175003 (2004)
10. A. Macchi et al., Phys. Rev. Lett. 103, 085003 (2009)
11. B. M. Hegelich et al., New J. Phys. 15, 085015 (2013)
12. L. Yin et al., Phys. Plasmas 14, 056706 (2007)
13. M.M. Günther et al., Nature Comm. 13, 170 (2022)
14. M. Roth et al., Phys. Rev. Lett. 110, 044802 (2013)
15. A. Kleinschmidt et al., Phys. Plasmas 25, 053101 (2018)
16. C. K. Huang et al., Appl. Phys. Lett. 120, 024102 (2022)
17. B. Martinez et al., MRE 7, 024401 (2022)
18. M. Zimmer et al., Nature Comm. 13, 1173 (2022)
19. O. N. Rosmej et al., PPCF 62, 115024 (2020)
