Investigation on the transport efficiency of fast electrons with double-layer Kα fluorescence measurement.

Ultraintense laser driven fast electrons play an increasingly important role in many applications. To predict and optimize the fast electron transport efficiency, we introduce a one-dimensional analytical model including resistive effects to estimate the transport efficiency as a function of transport distance and a key parameter named the penetration path. Based on the model, the transport efficiency of fast electrons with the same penetration coefficient can be calculated for different characteristic parameters including the target thickness and laser intensity. A double-layer Kα fluorescence measurement of fast electron transport efficiency is proposed to eliminate the influence of in-target electrons refluxing from the relative Kα photon yield of the rear and front sides of the target. By fixing the transport distance, we have experimentally measured the penetration path and the efficiency of planar Al2O3 targets, in good accordance with Monte Carlo simulations. The results show that the beam energy can be reduced to 25% in a penetration path of tens of microns. This measurement method provides a feasible route to characterize and compare the fast electron transport in various targets and laser conditions, making it possible to modulate and optimize the transport efficiency in actual research studies, which is of great significance in fast ignition, X-ray emission, positron–electron pair production, and many other applications. [ABSTRACT FROM AUTHOR]