High performance of laser-driven sources of radiation is in focus of research aimed at the study of high energy density matter, pair production and neutron generation using kJ PW-laser systems. In this work, we present a highly efficient approach to generate an ultra-high flux, high-energy bremsstrahlung in the interaction of direct laser-accelerated (DLA) electrons with a several-millimeters-thick high-Z converter. A directed beam of direct laser-accelerated electrons with energies up to 100 MeV was produced in the interaction of a sub-ps laser pulse of moderate relativistic intensity with long-scale plasma of near-critical density obtained by irradiation of low-density polymer foam with an ns laser pulse. In the experiment, tantalum isotopes generated via photonuclear reactions with threshold energies above 40 MeV were observed. The Geant4 Monte Carlo code, with the measured electron energy and angular distribution as input parameters, was used to characterize the bremsstrahlung spectrum responsible for the registered yields of isotopes from 180Ta to 175Ta. It is shown that when the direct laser-accelerated electrons interact with a tantalum converter, the directed bremsstrahlung with an average photon energy of 18 MeV and ∼2⋅1011 photons per laser shot in the energy range of giant dipole resonance (GDR) and beyond (≥7.5 MeV) is produced. This results in an ultra-high photon flux of ∼6 × 1022 sr−1·s−1 and a record conversion efficiency of 2% of the focused laser energy into high-energy bremsstrahlung.
A neural network-based approach is proposed both for reconstructing the focal spot intensity profile and for estimating the peak intensity of a high-power tightly focused laser pulse using the angular energy distributions of protons accelerated by the pulse from rarefied gases. For these purposes, we use a convolutional neural network architecture. Training and testing datasets are calculated using the test particle method, with the laser description in the form of Stratton–Chu integrals, which model laser pulses focused by an off-axis parabolic mirror down to the diffraction limit. To demonstrate the power and robustness of this method, we discuss the reconstruction of axially symmetric intensity profiles for laser pulses with intensities and focal diameters in the ranges of 1021–1023 W cm−2 and ∼(1–4) λ, respectively. This approach has prospects for implementation at higher intensities and with asymmetric laser beams, and it can provide a valuable diagnostic method for emerging extremely intense laser facilities.
Generation of terahertz radiation by an oscillating discharge, excited by short laser pulses, may be controlled by geometry of the irradiated target. In this work, an annular target with a thin slit is considered as an efficient emitter of secondary radiation when driven by a short intense laser pulse. Under irradiation, a slit works as a diode, which is quickly filled by dense plasmas, closing the circuit for a traveling discharge pulse. Such a diode defines the discharge pulse propagation direction in a closed contour, enabling its multiple passes along the coil. The obtained oscillating charge efficiently generates multi-period quasi-monochromatic terahertz waves with a maximum along the coil axis and controllable characteristics.
This work considers a solenoid-based magnetic collimation system for improving the efficiency of ion trap loading with ions created by laser ablation. We discuss a physical model of ion beam collimation in such a system, provide qualitative analytical estimates of its collimation characteristics, develop a numerical model of ion collimation based on a test-particle approach, and describe a real experimental setup where the proposed approach is effectively employed to collimate 232Th3+ and 88Sr1+ ions. The experimental results are compared with the results of the performed numerical modeling. The observed inconsistencies between the two are discussed, and their possible explanations are suggested.
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