Linearly polarized

The peak intensity of a multi-petawatt (PW) laser pulse can reach $10^{22}\,\mathrm {W/cm}^{2}-10^{23}\,\mathrm {W/cm}^{2}$ which is available recently. Here we investigate the generation of linearly polarized γ photons via a typical laser-solid setup that a linearly polarized laser is incident on a solid target with a micron-scale preplasma. Linear polarization characteristics of γ photons are examined using QED particle-in-cell (PIC) simulations with various laser amplitudes, solid target density, and preplasma density scale length. The simulation results indicate that linear polarization of radiated γ photons can exceed 60% in a low-energy domain, and all photons exhibit sufficiently high linear polarization degrees across various parameter conditions. The laser field and self-generated plasma field can accelerate electrons to ultra-relativistic energies. After the laser is reflected by the plasma, it can form a standing wave with the incident laser. In such a standing wave field, high-energy electrons can radiate a large number of polarized γ photons. Such a polarized γ photon source has a variety of applications such as nuclear science, high-energy physics, astrophysics and plasma physics.