P. Hagelstein

Relativistic distorted-wave calculations of electron collision cross sections and rate coefficients for Ne-like ions

Abstract Electron collision data are required for population kinetics modeling and spectral predictions of highly ionized ions in high-temperature plasmas. For highly stripped ions of moderate to high Z, relativistic effects begin to play a role in the atomic physics calculations. We describe numerical techniques which we have employed to compute relativistic distorted-wave inelastic electron collision cross sections from relativistic multiconfiguration bound states. As an application of these techniques, we have calculated full sets of cross sections and rate coefficients between all L-shell and M-shell states of the Ne-like ions Fe, Se. Y, Mo, and Ag.

Review of radiation pumped soft x-ray lasers

Three approaches to the problem of EUV and soft X-ray lasers are being pursued experimentally at the NOVETTE and OMEGA laser facilities. Photoionization pumping of neon gas may lead to a self- terminating population inversion in Ne II at 27 eV, and experiments planned at OMEGA are planned to observe amplified emission. Line radiation may be used to drive an inversion in helium-like or hydrogen- like fluorine and neon at energies between 53.6 and 151 eV. We have carried out an exploratory experimental sequence on NOVETTE designed to test integral laser targets. Experience gained points the way towards a second generation target design and future coincident spectroscopy and integral laser experiments. A third approach involves collisional excitation of 3p leading to a 3p-3s inversion near 68 eV. The scheme was tested at NOVETTE, and a null result obtained, which may be explained by beam bending caused by large index of refraction gradients. Phase correction is proposed as an improvement for the scheme.

Observation of soft x‐ray amplification in neonlike molybdenum

Thin molybdenum coated foils have been irradiated in line focus geometry with from 3 to 8×1014 W cm−2 of 0.53‐μm light at the Nova laser. The resulting exploding foil plasma has demonstrated x‐ray laser gain at four wavelengths (106.4, 131.0, 132.7, and 139.4 A), identified as 3s‐3p transitions in neonlike Mo. The J=0–1, a 3s–3p transition at 141.6 A has been identified, but does not show evidence of significant gain in disagreement with the theory.

Theory and design of soft x-ray laser experiments at the Lawrence Livermore National Laboratory

Recent progress in the design and analysis of soft X-ray laser experiments at the Lawrence Livermore National Laboratory is reviewed. The modelling of optical laser irradiated targets used to produce X-ray lasers is discussed. Two types of atomic inversion schemes have been explored-collisional excitation in neon-like and nickel-like ions, and recombination in lithium-like and hydrogen-like ions. Results for each scheme are discussed and compared with experimental data. The authors describe work on X-ray optics, including refraction by electron density gradients in the lasing plasma, techniques for increasing spatial coherence and the use of multilayer mirrors to improve laser efficiency and coherence.

A gas puff soft x‐ray laser target design

An x‐ray laser target to be driven by a Xe gas puff implosion powered by the Proto II machine at Sandia is proposed. The laser material is Sn pumped to the Ni‐like ionization state. The main laser transition (4d‐4p) is calculated to be near 110.5 eV.

The scaling of Ne‐like x‐ray laser schemes to short wavelength

The driver and target parameters required to extend the successful results from an exploding foil Ne‐like‐Se soft x‐ray laser at 206 A towards wavelengths of 40 A are investigated. The power requirements are found to scale as λ−4, which is quite costly. The principal constraint is the refraction of the x‐ray laser beam in these high density, single pass, exploding foil targets. Correcting mirrors or nonrefracting target designs could reduce this costly scaling.

Estimated gains for a Ni‐like exploding foil target

It is shown that an exploding Eu foil target irradiated with 7.5×1013 W/cm2 should reach plasma parameters which look optimistic for soft x‐ray lasing. Among the lines of interest are two 4p‐4d transitions near 100 A and two near 80 A with gains estimated at 4–7 cm−1.

Lawrence Livermore National Laboratory X-Ray Laser Research: Recent Results

Since the successful demonstration of gain in neon-like selenium using an exploding foil amplifier, the x-ray laser group at Lawrence Livermore National Laboratory has investigated further the exploding foil amplifier concept for use in XUV lasers. Results are reported of the characteristics of selenium amplifiers up to 50 mm in length. Observation of at least 16 gain lengths for the 206 Å line of selenium is reported. Output powers in excess of 1 MW have been measured in pulses of approximately 200 picoseconds. The effects of refraction on the performance of long amplifiers have been studied. The occurrence time of the x-ray laser output relative to the input heating pulse has been measured and found to be in disagreement with a recent model that suggests three-body recombination driven by rapid radiative cooling as the inversion process in the selenium plasma.

No pain—no gain: The complex art of soft x‐ray laser target design and analysis

We review our methodologies in the design and analysis of soft x‐ray laser experiments. We convolve large scale 2‐D hydro code output with detailed atomic data bases in a kinetics code with 1‐D or 2‐D line transfer. The time and space dependent level population data is then post processed further with a beam transport code, including refraction, to predict actual experimental results. While mysteries do remain, we present many examples that show how this complex modeling procedure is crucial in explaining experimental results.

Resonantly-Pumped Soft X-Ray Lasers Using ICF Drivers

The problem of developing a laser with a transition frequency in the EUV or soft X-ray regime is challenging, due primarily to the difficulty in developing an inversion on a line with appreciable gain under experimentally accessible conditions, and in part to the large local power requirements involved. The development of EUV and soft X-ray lasers would lead to advances in spectroscopy due to the potential for high brightness and narrow line width of the lasing radiation. There may be practical applications for a soft X-ray laser in the area of semiconductor photolithography. Short wavelegth holography may prove to be useful, assuming in both cases that the output laser radiation is sufficiently powerful, coherent and economical, and that production of the laser radiation can be carried out in a practical manner.