Momentum transfer to laser-irradiated targets, indicating the nonlinear interaction force

Measurements by Metz of the momentum ρ transferred to laser-irradiated targets are evaluated and compared with the results of the nonlinear force of laser-plasma interaction. The measured thresholds for the intensity I*, estimated to be 2 × 1014 W/cm2, agree with the threshold of the nonlinear force. The measured highly superlinear relation P ≈ I4 agrees very well with the theory for not too large intensities I≳ I*. A consequence would be an electron energy of coherent oscillation near 104 eV, which may cause a nonthermal origin of fusion neutrons in other experiments.