Ultrabright, well-collimated MeV bremsstrahlung radiation was generated through the interaction of high-current electron beams produced via direct laser acceleration (DLA) with a high-$Z$ converter. The DLA mechanism was initiated by a 200 TW, subpicosecond PHELIX laser pulse at a moderately relativistic intensity of (1–2) $\times {10}^{19}\mathrm{W}{\mathrm{cm}}^{-2}$, delivering approximately 60 J of energy into preionized, overcritical-density foam targets. The electron spectrum measured along the laser axis exhibited an effective temperature of approximately $30\mathrm{MeV}$ and energies exceeding 100 MeV, with a total charge of about 300 nC for electrons with energies $>1.5\mathrm{MeV}$ (ponderomotive potential), while 100 nC of them is directed along the laser axis within a half-angle cone of ${12}^{\circ }$. The directed fraction of DLA electrons with energies exceeding 7.5 MeV carries a charge of 20 to 30 nC, corresponding to a flux up to $2\times {10}^{24}{\mathrm{sr}}^{-1}{\mathrm{s}}^{-1}$. These high-current relativistic electron beams efficiently generate MeV x-rays, enabling the subsequent production of isotopes, positrons, and neutrons with exceptional yield and application potential. In laser shots employing overcritical-density foam targets placed in front of a high-$Z$ converter, bremsstrahlung photons with energies up to 70 MeV were generated and analyzed via nuclear activation of tantalum and gold. The formation of the isotopes ${}^{174}\mathrm{Ta}$ and ${}^{190}\mathrm{Au}$, whose photonuclear cross-section peaks at approximately 65 MeV, confirmed the presence of high-energy photons. In contrast, no activation was observed in control shots where the laser was directed onto the converter without foam, indicating that high-energy photon generation is intrinsically linked to the DLA process in the preionized foam targets. Autoradiographic measurements revealed a divergence of the bremsstrahlung beam of approximately ${22}^{\circ }$ (half-angle) in the 14–21-MeV range. These diagnostics indicate an unprecedented photon flux of approximately $2\times {10}^{22}{\mathrm{sr}}^{-1}{\mathrm{s}}^{-1}$, corresponding to about ${10}^{11}$ photons per shot with energies exceeding 7.5 MeV. The conversion efficiency of focused laser energy to bremsstrahlung photons is greater than 1% (within the FWHM of x-ray beam and laser beam). More than $2\times {10}^9$ photoneutrons per shot were emitted isotropically, corresponding to a peak flux of $2\times {10}^{20}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ ($4\times {10}^{18}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{J}}^{-1}$ of laser energy on target). This approach demonstrates a robust and scalable method for generating ultraintense MeV photon beams at kilojoule, petawatt-class laser facilities operating at moderate relativistic intensities, with strong implications for high-energy-density physics and nuclear astrophysics research.

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• High-energy-density plasmas
• Laser wakefield acceleration
• Laser-plasma interactions
• Photonuclear reactions
• Radiation & particle generation in plasmas
• Polymers
• Neutron techniques
• X-ray techniques