Superradiance is the anomalous radiance describing coherent photon emission from a gas. It plays a crucial role in atomic physics, quantum mechanics and astrophysics. Because the intensity of superradiant light beams is proportional to the number of particles squared, superradiance is also at the core of today’s most powerful light sources. Superradiant emission is intuitively expected when the distance between light-emitting particles is much smaller than the photon wavelength. Here, we break this assumption by predicting a never considered superradiance effect that holds even when the particle number per wavelength vanishes. We discover that a bunch of relativistic charged particles arranged in certain ways can generate an optical shock along the Vavilov–Cherenkov angle in vacuum, thereby concentrating broadband radiation in any spectral region into single light bullets. The process leaves clear experimental signatures, and we illustrate it in the form of a previously unrecognized nonlinear superradiant Thomson scattering. This concept may enable new forms of superradiant emission in advanced light sources, atomic physics systems, and unlock coherent emission in plasma accelerators.

超辐射是描述气体中相干光子发射的异常辐射。它在原子物理学，量子力学和天体物理学中起着至关重要的作用。因为超辐射光束的强度与平方的粒子数量成正比，所以超辐射也是当今最强大的光源的核心。当发光粒子之间的距离远小于光子波长时，可以直观地预期到超辐射发射。在这里，我们通过预测从未考虑过的超辐射效应来打破这一假设，即使每个波长的粒子数消失时，该效应也将保持。我们发现，以一定方式排列的一堆相对论带电粒子会在真空中沿Vavilov-Cherenkov角产生光冲击，从而将任何光谱区域中的宽带辐射集中到单个子弹中。该过程留下了清晰的实验特征，我们以以前无法识别的非线性超辐射汤姆森散射的形式对其进行了说明。该概念可以在高级光源，原子物理系统中实现新形式的超辐射发射，并在等离子体加速器中解锁相干发射。