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We give an overview of recent results on optical-field-ionization collisional soft X-ray lasers developed at LOA. By focusing a 30-fs, circularly polarized Ti-sapphire laser pulse at an intensity of up to 8 x 10 17 Wcm -2 into a low-density gas cell containing xenon or krypton, we produced a few mm long plasma column for soft X-ray amplifier. Saturated amplification has been achieved on the 4d 9 5d( 1 S 0 ) - 4d 9 5p( 1 P 1 ) transition at 41.8 nm in Pd-like Xe, and strong lasing at 32.8 nm on the 3d 9 4d( 1 S 0 ) - 3d 9 4p( 1 P 1 ) transition in Ni-like Kr has been demonstrated. Under optimum pumping conditions the Xe IX laser provides about 5 x 109 photons per pulse while the Kr IX laser delivers up to (2-3) x 10 9 photons per shot. The repetition rate of these X-ray lasers is 10 Hz. The experimental results are discussed and compared to computational simulations in which issues related to plasma formation, electron energy distribution, and atomic processes are addressed.

Numerical simulations have been performed for the collisionally pumped soft X‐Ray lasers in eight times ionized Kr and Xe which are driven by optical field ionisation of the gas by a high intensity femtosecond laser. Results are presented covering the expected state of the plasma formed, time dependant gain calculations and also a brief discussion on the nature of the electron distribution function.