Hundreds of Nanocoulomb Electron Acceleration Driven by Multipetawatt Laser in Subcritical Density Plasmas

High‐charge beams remain a key research focus in laser plasma acceleration, driven by the demands of extreme experimental conditions in nuclear physics, laboratory astrophysics, and fusion research. A distinct acceleration mechanism is presented in which the interaction between petawatt femtosecond laser pulses and the subcritical density (SCD) plasma produces electron beams with charges of hundreds of nanocoulomb (nC), far exceeding those typically achieved via conventional laser wakefield acceleration. The synergy between the multiwakefield structure in SCD plasma and the laser self‐steepening effect significantly enhances the electron injection rate to 100 nC ps −1 , experimentally achieving the electron beam charge up to 245 nC. This mechanism operates by reducing the phase velocity of plasma waves and increasing electron momentum, allowing large numbers of electrons to exceed the wave‐breaking threshold and undergo efficient injection. Experiments and simulations consistently confirm the dependence of charge on plasma density and laser energy, with charge reaching a maximum at a specific plasma density. Such high‐charge, high‐density electron beams offer promising applications in high‐flux particle beam physics, large‐field‐of‐view industrial imaging, advanced light sources, and radiation‐hardness testing of electronic systems.