Enhanced Inverse Compton Scattering via Spontaneous Focusing induced by Coated Plasma Mirror

Efficient generation of high-energy γ-rays from laser-electron interactions is crucial for advancing nuclear photonics and strong-field quantum electrodynamics (QED). However, the energy-conversion efficiency of plasma-mirror-based all-optical inverse Compton scattering (ICS) has been fundamentally constrained by the limited overlap between the reflected laser pulse and the wakefield-accelerated electron beam. Here we experimentally demonstrate a coated plasma mirror that spontaneously focuses the reflected pulse, substantially enhancing the local field intensity and driving strongly nonlinear multiphoton ICS. Experiments show that the coating improves the laser-to-radiation energy conversion efficiency by nearly an order of magnitude compared with uncoated mirrors, at the level of 10^-4-10^-3, with photon energies extending from tens to hundreds of MeV. This simple yet robust approach overcomes the intrinsic energy-utilization limit of plasma-mirror ICS and offers a scalable route toward compact, high-brightness γ-ray sources for table-top strong-field QED studies and nuclear photonics applications.