Yield Optimization and Time Structure of Femtosecond Laser Plasma Kα Sources

The generation of femtosecond Kα x rays from laser-irradiated plasmas is studied with a view to optimizing photon number and pulse duration. Using analytical and numerical models of hot electron generation and subsequent transport in a range of materials, it is shown that an optimum laser intensity I_opt  =  7×10⁹Z^4.4 exists for maximum Kα yield. Furthermore, it is demonstrated that bulk targets are unsuitable for generating sub-ps x-ray pulses: instead, design criteria are proposed for achieving Kα pulse durations ≤100 fs using foils of ≈2 μm thickness.