In a giant‐pulse laser rod an inhomogeneous excess inversion across the rod diameter will lead to a non‐uniform growth rate of the photon avalanche, when the transverse modes are not tightly coupled. For a model inversion distribution the resulting giant‐pulse elongation is calculated. The radial time dispersion can be compensated by a radius‐dependent resonator feedback or by transverse mode coupling. The influence of thermal resonator curvature on the decoupling of transverse modes is discussed.