High-resolution coherent transition radiation (CTR) imaging diagnoses electrons accelerated in laser—solid interactions with intensities of $\sim {10}^{19}\mathrm{W}/{\mathrm{cm}}^2$. The CTR images indicate electron-beam filamentation and annular propagation. The beam temperature and half-angle divergence are inferred to be $\sim 1.4\mathrm{MeV}$ and $\sim 16°$, respectively. Three-dimensional hybrid-particle-in-cell code simulations reproduce the details of the CTR images assuming an initial half-angle divergence of $\sim 56°$. Self-generated resistive magnetic fields are responsible for the difference between the initial and measured divergence.

• Received 23 February 2009

DOI:https://doi.org/10.1103/PhysRevLett.102.235004