Coherent soft X-ray lasing from Ni-like Mo plasma in transient gain amplification scheme

Generation of molybdenum plasma by a long pulse is reported. Optimization of various experimental parameters (pulse delay, pulse energy ratio, target positioning, etc.) together with appropriate excitation scheme and pumping geometry allows to achieve the initial stages of lasing regime even for pulse energies below 1 Joule. The intensity of the X-ray laser radiation depended on the delay between the long and short pumped pulses. Maximal signal was registered at 0.5 - 1-ns delay. A ratio between the heating pulses´ energies (k = E_fs/ E_ps) has changed from 0.3 to 10. The optimal conditions in this geometry were found to be at k = 3. Another important parameter is the distance between the target and focal point of femtosecond radiation. The maximal signal was registered at the distance of 0.2 - 0.3 mm from the Mo surface. The full energy of the pumping radiation was less than 0.5 J.