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Saturation of a low pump energy x-ray laser utilizing a transient inversion mechanism on the 3 p-3s transition at 32.63 nm in Ne-like Ti has been demonstrated. A close to saturation amplification was simultaneously achieved for the 3d-3p, Jϭ1→1 transition at 30.15 nm. Small signal effective transient gain coefficients of gϳ46 and ϳ35 cm Ϫ1 and gain-length products of 16.7 and 16.9 for these lines were obtained. Experiments demonstrate that it is possible to achieve saturated laser action in a transient regime with Ne-like Ti for a pump energy as low as ϳ5 J.

Small fluctuations in the acceleration sheath change the pointing of a proton beam accelerated from the rear side of a laser irradiated thin aluminum foil. The proton acceleration was produced with 40 fs pulses of a Ti:sapphire laser at an intensity of approximately 10 19 W/cm 2 . This observation has been made with a high spatial resolution Thomson spectrometer. The proton beam pointing has appeared stable in the energy range between the high energy cutoff ͑3 MeV͒ and 50% of this value. Deviations of the beam position at lower energies changes in a range of 0 -3 mrad. The recorded pictures show wiggled and continuous proton traces which imply a release of the proton beam from the acceleration zone with a velocity chirp.

We report on a demonstration of x-ray-ultraviolet amplification following collisional excitation in a discharge-created plasma waveguide irradiated by a picosecond optical laser pulse. A capillary discharge was used to generate a sulfur plasma column with a large concentration of Ne-like ions and a radially concave electron density profile. The intense short laser pulse rapidly heated the electrons, producing amplification in the 3p 1 S 0 -3s 1 P 1 transition of Ne-like S at 60.8 nm. The integrated gain-length product obtained exciting a 3-cm-long capillary with a 0.46-J short laser pulse is 6.8. The beam divergence was observed to decrease as a function of plasma column length, reaching 2.5 mrad for 30-mm-long capillaries. This hybrid laser pumping scheme could lead to a new generation of efficient tabletop soft-x-ray lasers. In recent years soft-x-ray lasers ͑XRLs͒ have evolved toward more compact systems based on efficient pumping schemes. Several laser excitation schemes based on either collisional electron excitation ͓1-3͔ or plasma recombination ͓4,5͔ have been investigated for the development of tabletop soft XRL's. To date, two different robust pumping methods for the excitation of compact collisional XRL's have succeeded in demonstrating a laser output energy у10 J. One is based on the generation of a transient population inversion in a laser-created plasma ͓3,6,7͔, and the other in the excitation of elongated plasma columns using fast capillary discharges ͓1͔. In the second scheme the electromagnetic force of the discharge current causes the capillary plasma column to rapidly pinch, and its density and temperature to increase markedly, creating a large quasi-steady-state density of excited Ne-like ions ͓1͔. Capillary discharge excitation has resulted in saturated laser amplification in Ne-like Ar at 46.9 nm ͓8͔ and Ne-like Cl at 52.9 nm ͓9͔. Further developments resulted in the generation of 46.9-nm nanosecond laser pulses with an average laser pulse energy of 880 J at a repetition rate of 4 Hz, corresponding to an average power of 3.5 mW ͓10͔. In turn, the transient excitation collisional scheme, which is based in the rapid heating of a precreated plasma with an intense picosecond laser pulse, has produced picosecond x-ray laser pulses at wavelengths as short as 7 nm ͓11͔. It has reduced by nearly two orders of magnitude the energy necessary to drive laser-pumped collisional softx-ray lasers to saturation. The first experiment involving transient collisional excitation resulted in the demonstration of a gain coefficient of 19 cm Ϫ1 at 32.6 nm in Ne-like Ti ͓3͔. Further developments resulted in the saturation of the output in Ne-like Ge and Ti ͓6,7͔, and more recently the demonstration of saturated lasers with a ϳ10-J output pulse energy in Ni-like Pd ( ϭ14.7 nm) and Ag ( ϭ13.9 nm) using ϳ7 J of total optical laser energy ͓12,13͔. In the standard version of the transient excitation scheme a combination of long and short laser pulses is made to impinge on a solid target to create and subsequently rapidl...

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