Generating Vector-Vortex $γ$ Photons by Nonlinear Compton Scattering

However, their generation in the $γ$-ray regime remains challenging. Here, we put forward a novel method to generate vector-vortex $γ$ photons via nonlinear Compton scattering in elliptically polarized laser pulses.

We reveal that tailoring laser ellipticity directs the multiphoton absorption to coherently populate OAM modes with opposite winding numbers, $\pm \ell$, tied to orthogonal circular polarizations, producing nonseparable spin-OAM photon states. For a linearly polarized laser of moderate intensity (dimensionless amplitude $a_0 \sim 1$), the mode-pair concurrence--a 0-to-1 measure of spin-OAM entanglement--reaches unity for MeV $γ$ photons, realizing maximally nonseparable radial- or azimuthal-type vector-vortex states.