Soft x-ray lasing at 18.9 nm and 20.3 nm in nickel-like molybdenum and niob
ium ions has been demonstrated using two 200 ps laser pulses with similar t
o0.2TW laser power at 1.053 mum from XingGuang II laser facility. A compari
son has been made of performance of the neon-like chromium soft x-ray lasin
g at 28.5nm driven by a double 900 ps pulse at 6 TW/cm2, compare to that dr
iven by a double 200 ps pulse at similar irradiance. The 900 ps pulse durat
ion was found to be able to provide stronger emission and narrower divergen
ce of neon-like chromium soft x-ray lasing.