Travelling wave chirped pulse amplified transient pumping for collisional excitation lasers

A similar to 3 ps travelling wave chirped pulse amplified pulse at 6 x 10(14) W cm(-2) superimposed on similar to 300 ps background pulses is shown to be an efficient method to pump transient collisional excitation X-ray lasers in both Ni-like and Ne-like ions. Measurements of X-ray laser output as a function of plasma length are fitted with results of an amplified spontaneous emission model of the laser output taking account of travelling wave pumping effects. A small signal gain coefficient similar to 42 cm(-1) and a effective gain length product of similar to 18 are measured for the Ni-like Sn laser at 120 Angstrom. Simulations from a hydrodynamic and atomic physics code (EHYBRID) coupled to a ray trace code show that a spatially averaged small signal gain similar to 65 cm(-1) can be obtained in Ne-like Ge provided the optimum pumping pulse arrangement is used. (C) 1999 Elsevier Science B.V. All rights reserved.

EXPERIMENTAL STUDIES OF THE MNF PHOTORESONANT EXCITATION SOFT-XRL SCHEME

Photoresonant excitation has been examined as a mechanism for enhancing the maximum gain achievable on a H-like recombination scheme. Modelling of the system, using the MED101/NIMP package, has shown that the photoresonant excitation of the 1s-3p (Ly(beta)) transition at 12.644 angstrom in a H-like fluorine plasma by a Be-like manganese transition at 12.643 angstrom offers the possibility of considerable gain enhancement on the 3d-2p Balmer alpha at 80.91 angstrom over the simple H-like system. Some experimental evidence for a transitory increase in intensity on the Balmer-alpha has been obtained for a fluorine-coated C-fiber system pumped by irradiating a manganese stripe in close proximity to the fiber.

CROSS-SECTIONS FOR RESONANT TRANSFER AND EXCITATION IN FEQ++H-2 COLLISIONS

Resonant transfer and excitation (RTE) is investigated for Fe(q+) ions (q=23, 24, and 25) colliding with H2. For each charge state, cross sections for RTE were obtained from measurements of K x rays, emitted from the doubly excited intermediate state, coincident with single-electron capture by the incident ion. Additionally, for Fe25+ cross sections were obtained from measurements of coincidences between the two K x rays emitted from the intermediate state. These latter measurements Provide information on the lifetimes of intermediate metastable states formed in the RTE process. In all cases, measured cross sections are in good agreement with calculations based on theoretical cross sections for dielectronic recombination (DR). Since RTE closely approximates DR, the results indicate that dielectronic-recombination cross sections involving K-shell excitation can be accurately predicted for highly charged iron ions. The results for Fe25+ show that metastable states are sufficiently short lived to be observable in the RTE (or DR) process for these hydrogenlike ions.