OPTIMIZATION OF DOUBLE DRIVE PULSE PUMPING IN NE-LIKE GE X-RAY LASERS

Pumping of the Ne-like Ge x-ray laser with two 100 ps duration pulses (a prepulse and main pulse) is investigated using a fluid and atomic p hysics code coupled to a 3D ray tracing postprocessor code. The modeli ng predicts the optimum ratio of the irradiance of the two pulses for the maximum x-ray laser output resulting from the balance between the relative lower electron density gradients and wider gain region which is produced with a larger prepulse and the higher peak gain coefficien ts produced with a small prepulse. With a longer pulse interval betwee n prepulse and main pulse, a relatively lower optimum pulse ratio is f ound. The threshold irradiance of the main driving pulse with a prepul se required to make an order of magnitude enhancement of laser output compared to irradiation without a prepulse is also found at 3-4x10(13) W/cm(2) for Ne-like Ge. (C) 1998 American Institute of Physics.