Polarization-resolved attosecond gamma-ray emission from few-cycle laser interactions with cone targets

Linearly polarized attosecond $\gamma$-ray pulses in the MeV range are generated from a cone target irradiated by a single few-cycle laser pulse. Electron layers are periodically extracted from the cone walls and subsequently accelerated. Their interaction with the counter-propagating reflected attosecond field produces high-energy photons through nonlinear Compton scattering (NCS), forming attosecond $\gamma$-ray pulses. We model this interaction using two-dimensional quantum electrodynamics particle-in-cell (QED-PIC) simulations that resolve electron spin and photon polarization during emission. The results show a shortest equivalent duration of $300\,\mathrm{as}$, with a corresponding linear polarization degree of 0.78. The photon spectrum extends to $6\,\mathrm{MeV}$, and the linear polarization degree in the high-energy range reaches 0.88. The linear polarization degree remains high when photons from both emission directions are collected over wide momentum-angle ranges. Scans over the cone opening angle and the coupled laser-plasma parameters reveal tradeoffs among photon number, mean photon energy, and polarization. Such highly polarized attosecond $\gamma$-ray pulses could be used to investigate ultrafast nuclear dynamics and polarization-dependent processes in strong-field quantum electrodynamics.