Ultrahigh-gain Ni-like Kr soft x-ray laser by optical field ionization-initiated transient collisional excitation scheme

We propose a Ni-like Kr soft x-ray laser operating on the 4d 1 S 0 - 4p 1 P 1 transition at 32.8 nm by a novel excitation scheme in which optical field ionization prepares Ni-like Kr ion with almost 100% abundance and inverse bremsstrahlung heats the plasma efficiently. The numerical calculation based on the hot-spot model predicts that ultra-high gains greater than 1000 cm -1 in the low density plasma (N e equals 5.6 X 10 19 cm -3 ) for a driving laser intensity of 1.75 X 10 16 W/cm 2 . With a longitudinally pumping, output energy greater than 1 (mu) J and an energy efficiency of approximately 10 -5 are expected with 200-torr Kr gas.