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We give an overview of recent experimental 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 8×1017 Wcm-2 into a low-density gas cell containing Xe or Kr, we produced a few mm long plasma column for soft X-ray amplifier. Saturated amplification has been achieved on the 4d95d(1 S 0)–4d95p(1 P 1) transition at 41.8 nm in Xe8+, and on the 3d94d(1 S 0)–3d94p(1 P 1) transition in Kr8+ at 32.8 nm. Under optimum pumping conditions the Xe8+ laser provides about (5±2)×109 photons per pulse whilst the Kr8+ laser delivers up to (2.5±1)×109 photons per shot. The repetition rate of these soft X-ray lasers is 10 Hz. The beam wavefront of the Xe8+ laser has been measured by a Shack–Hartmann soft X-ray wavefront sensor, and the pulse duration by a cross-correlation technique.

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.

International audience; Nous présentons de récents travaux sur la production de sources lasers XUV collisionels pompés par des impulsions laser femtoseconde. Le milieu amplificateur est un plasma créé d'ions multi-chargés et l'effet laser est observé sur les transitions 5p-5d à 41,8 nm du xénon IX et 4d-4p du krypton IX à 32,8 nm. L'influence des conditions d'irradiation et de densité du milieu lasant sur l'intensité de la source est présentée et discutée.

Current high power femtosecond lasers have been shown to produce electron pulses which may be appropriate for the pumping of X‐Ray lasers through collisional ionisation. Non‐radiative Coster‐Kronig type decay processes may be fast enough to form an inverted state and allow X‐ray lasing within the biologically interesting “water window”. Calculations of the atomic processes in metallic Ti, Mn and Cu are presented that potentially useable gains on the M1 − L3 transition.

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.