Characterization of collisionally pumped optical-field-ionization soft X-ray lasers

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 8x10(17) 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 4d(9)5d(S-1(0))-4d(9)5p(P-1(1)) transition at 41.8 nm in Xe8+, and on the 3d(9)4d(S-1(0))-3d(9)4p(P-1(1)) transition in Kr8+ at 32.8 nm. Under optimum pumping conditions the Xe8+ laser provides about (5+/-2)x10(9) photons per pulse whilst the Kr8+ laser delivers up to (2.5+/-1)x10(9) 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.