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

We propose a novel transient collisional excitation scheme for Ni-like Kr (4d 1 S 0 -4p 1 P 1 ) soft-x-ray laser at 32.8 nm. In this scheme, Kr atoms in a differentially pumped cell are longitudinally pumped by a picosecond Nd:glass laser pulse with a focal intensity of 2 × 10 16 W/cm 2 . Almost 100% of the Ni-like Kr ions are produced by optical-field-ionization, and the ps-pulse efficiently heats the Kr plasma by inverse bremsstrahlung. Numerical calculations predict that an ultrahigh-gain of greater than 1200 cm -1 is possible for the Ni-like Kr transition at 32.8 nm. Preliminary experimental results are also reported.