Double‐Plasmon Excitation in a Free‐Electron Gas

The interaction of a fast charged particle moving in a free‐electron gas is described in the random phase approximation (RPA). The mean free path for the second order process of double‐plasmon excitation in the free‐electron gas is calculated. We find that the inverse mean free path for the double‐plasmon excitation process is related to the inverse mean free path for single plasmon excitation by λ = 0.0103 r λ−1p. Thus, for electron densities corresponding to those in a real metal (1 < rs < 6) double‐plasmon excitation may be important in the interpretation of certain experimental results as, for example, characteristic energy loss measurements.