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Ion expansion energy measurements in plasmas created by focusing 1‐GW, 5‐nsec Nd:glass laser on plane solid targets of polythene, carbon, and aluminum are reported. It is observed that the scaling of ion expansion energy with laser flux Φ varies between Φ0.28 and Φ0.66 for polythene, Φ0.28 and Φ0.70 for carbon, and Φ0.51 and Φ0.44 for aluminum in the flux range 5×1010–5×1012 W/cm2 of our experiment. The scaling is either much slower or faster than a scaling of Φ4/9 expected from a self‐regulating model for plasmas created in the low flux range. It is shown that this behavior, as well as results of experiments on similar plasmas reported by other authors, can be explained when radiation losses and the energy spent in ionization are also considered in the self‐regulating model.