On the Origin of Super-Hot Electrons in Intense Laser-Plasma Interactions

Over the last decade, laser facilities with peak intensity I > 5 ∗ 10 W cm2 have pushed the limits of ion acceleration [1], x-ray generation [2], and laboratory astrophysics [3] to exciting new extremes. The essential element for all of these phenomena is the population of relativistic electrons produced by the laser-plasma interaction (LPI), often in the preformed plasma created by amplified spontaneous emission incident on the target starting a few ns before the short-pulse laser. The typical observed electron energy spectrum [4–7] can be broken into three different energy ranges. The low energy region (up to a few MeV) is poorly connected to the LPI as it is strongly modified by large rear-surface fields and ion production [7]. The second group of electrons, whose energy distribution is ponderomotive, has been described by several scaling laws [8–11] and is still not fully understood. For instance, reference [8] finds that