This graphic shows the secondary process by which XFEL light can drive the energy release from a sample containing a nuclear isomer. In the first step (top), photons knock electrons out of inner atomic shells. leading to a plasma of free electrons and ionized atoms. This interaction does not directly affect the nucleus, as it remains in the metastable isomeric state (top right). However, when electrons from the plasma are later captured in the inner-shell vacancies, their excess energy can excite the nucleus to a higher, but less stable, energy state (middle). In the last step, the nucleus relaxes to its ground state, releasing photons in a cascade (bottom).