Description
Relativistic circularly polarized (CP) mid-infrared (mid-IR) laser sources have many applications in strong-field physics and ultrafast science, such as laser wakefield acceleration, ultrahigh-order harmonic generation and attosecond pulse radiation. In this talk, we will show a new scheme for the generation of relativistic polarization-tunable mid-IR pulses. When an intense linearly polarized (LP) laser propagates through the underdense plasma with an applied transverse magnetic field, two key physical processes occur simultaneously: On the one hand, the laser excites a nonlinear plasma wake, where photon deceleration in the density upramp of the wake converts the near-IR laser into broadband mid-IR radiation. On the other hand, the relativistic magneto-birefringence effect induces a phase difference between ordinary (O) and extraordinary (X) wave components, which enables tuning from linear polarization to circular polarization. Three-dimensional (3D) particle-in-cell (PIC) simulations demonstrate the generation of relativistic polarization-tunable few-cycle (~2 cycles) mid-IR pulses from 6.25 to 16.67 µm, with polarization states precisely turned by applied magnetic fields. This all-optical, damage-free approach overcomes the intensity limitations of conventional crystal-based methods, bringing unique opportunities for attosecond science, strong-field physics, etc.
