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Modeling of the 3D spatio-temporal thermal profile of joule-class -based laser amplifiers
摘要： Thermal pro?le modi?cation of an active material in a laser ampli?er via optical pumping results in a change in the material’s refractive index, and causes thermal expansion and stress, eventually leading to spatial phase aberrations, or even permanent material damage. For this purpose, knowledge of the 3D spatio-temporal thermal pro?le, which can currently only be retrieved via numerical simulations, is critical for joule-class laser ampli?ers to reveal potentially dangerous thermal features within the pumped active materials. In this investigation, a detailed, spatio-temporal numerical simulation was constructed and tested for accuracy against surface thermal measurements of various end-pumped Yb3+-doped laser-active materials. The measurements and simulations show an excellent agreement and the model was successfully applied to a joule-class Yb3+-based ampli?er currently operating in the POLARIS laser system at the Friedrich-Schiller-University and Helmholtz-Institute Jena in Germany.
关键词： diode-pumped solid-state lasers,ytterbium,laser ampli?ers,spatio-temporal thermal pro?le modeling,high intensity lasers
更新于2025-09-19 17:13:59
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Experimental investigation on nuclear reactions using a laser-accelerated proton and deuteron beam
摘要： We report an experimental investigation on nuclear reactions using an intense, ultra-short laser-accelerated proton and deuteron beam generated by the interaction of 25 fs, 150 TW Ti: sapphire laser pulse with normal thin foils and foils containing deuterium atoms. The production of a positron-emitting short-lived 11C radio-isotope from the interaction of protons and deuterium ions with a solid boron palette by means of 11B (p, n)11C and 10B (d, n)11C nuclear reactions was studied. The maximum radioactivity in the optimized laser irradiation condition was found to be 5.2 kBq per laser shot, which corresponds to ～9 × 106 atoms of 11C isotopes using the 11B (p, n)11C reaction. The relative ef?ciency of 11C production using a proton and deuteron beam was also explored experimentally. About 30 % enhancement in 11C activity was observed with CD2 coated targets. It was also found that because of the relatively low deuteron energy threshold of the reaction 10B (d, n)11C, even the low energy part of the accelerated deuterons in the spectrum can be used for ef?cient 11C production. In the same setup, the proton-induced fusion reaction in the boron target (p + 5B11 ? 3α + 8.7 MeV) was also studied. The resultant fusion yield and alpha particle energy spectrum was measured.
关键词： p?11B fusion,laser particle acceleration,positron emission tomography (PET) isotopes,laser driven ion acceleration,laser plasma interaction,laser induced nuclear reactions,high intensity lasers
更新于2025-09-19 17:13:59
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Proton beam emittance growth in multipicosecond laser-solid interactions
摘要： High intensity laser-solid interactions can accelerate high energy, low emittance proton beams via the target normal sheath acceleration (TNSA) mechanism. Such beams are useful for a number of applications, including time-resolved proton radiography for basic plasma and high energy density physics studies. In experiments using the OMEGA EP laser system, we perform the first measurements of TNSA proton beams generated by up to 100 ps, kilojoule-class laser pulses with relativistic intensities. By systematically varying the laser pulse duration, we measure degradation of the accelerated proton beam quality as the pulse length increases. Two dimensional particle-in-cell simulations and simple scaling arguments suggest that ion motion during the rise time of the longer pulses leads to extended preformed plasma expansion from the rear target surface and strong filamentary field structures which can deflect ions away from uniform trajectories and therefore lead to large emittance growth.
关键词： ion acceleration,high-intensity lasers,plasma physics
更新于2025-09-19 17:13:59
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Axiparabola: a long-focal-depth, high-resolution mirror for broadband high-intensity lasers
摘要： Diffraction puts a fundamental limit on the distance over which a light beam can remain focused. For about 30 years, several techniques to overcome this limit have been demonstrated. Here, we propose a reflective optics, namely, the axiparabola, that allows to extend the production of “diffraction-free” beams to high-peak-power and broadband laser pulses. We first describe the properties of this aspheric optics. We then analyze and compare its performances in numerical simulations and in experiments. Finally, we use it to produce a plasma waveguide that can guide an intense laser pulse over 10 millimeters.
关键词： broadband high-intensity lasers,high-resolution mirror,axiparabola,plasma waveguide,long-focal-depth
更新于2025-09-12 10:27:22
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Plasma optics in the context of high intensity lasers
摘要： The use of plasmas provides a way to overcome the low damage threshold of classical solid-state based optical materials, which is the main limitation encountered in producing and manipulating intense and energetic laser pulses. Plasmas can directly amplify or alter the characteristics of ultra-short laser pulses via the three-wave coupling equations for parametric processes. The strong-coupling regime of Brillouin scattering (sc-SBS) is of particular interest: recent progress in this domain is presented here. This includes the role of the global phase in the spatio-temporal evolution of the three-wave coupled equations for backscattering that allows a description of the coupling dynamics and the various stages of amplification from the initial growth to the so-called self-similar regime. The understanding of the phase evolution allows control of the directionality of the energy transfer via the phase relation between the pulses. A scheme that exploits this coupling in order to use the plasma as a wave plate is also suggested.
关键词： Brillouin scattering,wave plate,high intensity lasers,Plasma optics,laser-plasma interaction
更新于2025-09-12 10:27:22