We present progress in experiments for high efficiency Ne-like and Ni-like ion x-ray lasers using the transient collisional excitation scheme. Experimental results have been obtained on the COMET 15 TW table-top laser system at the Lawrence Livermore National Laboratory (LLNL). The plasma formation, ionization and collisional excitation of the x-ray laser have been optimized using two sequential laser pulses of 600 ps and 1 ps duration with an optional pre-pulse. We have observed high gains up to 55 cm~(-1) in Ne-like and Ni-like ion schemes for various atomic numbers. We report strong output for the Ad - 4p line in lower Z Ni-like ion sequence for Mo to Y, lasing from ～190 A to 240 A, by pumping with less than 5 J energy on target.
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