Yield optimization and time structure of femtosecond laser plasma Kα sources

The generation of femtosecond K alpha 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 X 10(9)Z(4.4) exists for maximum K alpha yield. Furthermore. it is demonstrated that bulk targets are unsuitable for generating sub-ps x-ray pulses: instead, design criteria are proposed for achieving K alpha pulse durations less than or equal to 100 fs using foils of approximate to 2 mu m thickness.