High-Energy Photon Generation from Self-Organized Plasma Cavities in Field-Enhanced Laser-Preplasma Interactions

The interaction of an ultraintense Nd:glass laser pulse with a near-critical plasma self-organizes into a highly efficient $\gamma$-ray source. Three-dimensional particle-in-cell simulations demonstrate that relativistic self-focusing, aided by a self-generated electron cavity, enhances the laser intensity by more than an order of magnitude, driving the system into the radiation-reaction-dominated regime, i.e. one where the electrons lose a substantial amount of their energy as hard radiation. Peak photon emission occurs near $0.5$ times the relativistic critical density, with a $\gamma$-photon yield exceeding $20\%$ of the laser energy. Compared to Ti:Sa lasers of the same power, the longer duration of Nd:glass laser pulses leads to an order of magnitude increase in $\gamma$-photon number in the extreme conversion efficiency regime, making them particularly well-suited for photonuclear physics applications. These findings point to a robust and scalable mechanism for compact, ultra-bright $\gamma$-ray generation in the multi-petawatt regime.