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Title: Optimizing the performance of nickel-like collisionally pumped x-ray lasers

Abstract

The development of soft x-ray lasers collisionally pumped by a relatively long prepulse and short main pulse has markedly improved the effectiveness of these devices. As a result it is possible to envisage their use in a well equipped university laboratory. In this note we break down the various elements of the interaction and pumping into their simple components in order to see how relatively simple analytic concepts can be used to identify the best mode of operation. However detailed simulation is still required to identify the actual experimental operating conditions. The scaling results are compared with simulation, confirming the value of this analysis.

Authors:
 [1]
  1. Department of Physics, University of York, Heslington, York YO10 5DD (United Kingdom)
Publication Date:
OSTI Identifier:
20786989
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. A; Journal Volume: 73; Journal Issue: 3; Other Information: DOI: 10.1103/PhysRevA.73.033809; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; COMPUTERIZED SIMULATION; LASER RADIATION; OPTICAL MODES; OPTICAL PUMPING; PERFORMANCE; PULSES; SOFT X RADIATION; X-RAY LASERS

Citation Formats

Pert, G. J. Optimizing the performance of nickel-like collisionally pumped x-ray lasers. United States: N. p., 2006. Web. doi:10.1103/PHYSREVA.73.0.
Pert, G. J. Optimizing the performance of nickel-like collisionally pumped x-ray lasers. United States. doi:10.1103/PHYSREVA.73.0.
Pert, G. J. Wed . "Optimizing the performance of nickel-like collisionally pumped x-ray lasers". United States. doi:10.1103/PHYSREVA.73.0.
@article{osti_20786989,
title = {Optimizing the performance of nickel-like collisionally pumped x-ray lasers},
author = {Pert, G. J.},
abstractNote = {The development of soft x-ray lasers collisionally pumped by a relatively long prepulse and short main pulse has markedly improved the effectiveness of these devices. As a result it is possible to envisage their use in a well equipped university laboratory. In this note we break down the various elements of the interaction and pumping into their simple components in order to see how relatively simple analytic concepts can be used to identify the best mode of operation. However detailed simulation is still required to identify the actual experimental operating conditions. The scaling results are compared with simulation, confirming the value of this analysis.},
doi = {10.1103/PHYSREVA.73.0},
journal = {Physical Review. A},
number = 3,
volume = 73,
place = {United States},
year = {Wed Mar 15 00:00:00 EST 2006},
month = {Wed Mar 15 00:00:00 EST 2006}
}
  • Soft x-ray lasers operating in the super- 100 A ring regime and using grazing incidence pumping methods are now established as efficient sources of radiation in this waveband. The concepts underlying this approach are to separate the ionization and excitation phases of the laser, and to match the pumping density of the latter to the optimal for gain generation. It is therefore of considerable interest to examine whether these ideas can be successfully applied to sub-100 A ring lasers. Three problems arise: first the adverse scaling of ionization with temperature for high atomic number ions, second the strong thermal conductionmore » at these temperatures leads to a large hot zone upstream of the absorption, and third the optimum pumping density is greater than the critical density of 1 {mu}m wavelength, solid state pump lasers. Using analytic models and simulation we identify a strategy to overcome these problems using a pre-pulse of a mixed harmonic and fundamental radiation of Nd-glass laser radiation followed by the main pumping pulse of the fundamental normally incident. Due to the large upstream thermal zone and the high ionization temperature, we find that the energy required in the pre-pulse is much ({approx}3 times) larger than that in the main, and that the energy needed consequently scales rapidly with the atomic number and therefore decreasing x-ray wavelength. Systems generating output energies of a few tens of {mu}J are examined at wavelengths between 50 and 70 A ring.« less
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  • Results of numerical simulations on a Ni-like silver x-ray laser pumped by a single picosecond laser pulse are presented. Since the mechanisms responsible for the significant reduction in the pump energy are not well understood, the results of theoretical simulations with emphasis on the plasma kinetics and dynamics in a Ni-like Ag x-ray laser are presented and referred to the experimental data. Special attention has been paid to the influence of the pump pulse shape and length on the gain and its duration. It was found that a low-level pulse pedestal being an integral part of the leading edge ofmore » the pump pulse is very beneficial to the pump energy reduction. The thermal cooling process has been identified as the mechanism strongly contributing to gain termination if a low-energy single-profile laser pulse with the width of a few picoseconds is used in the pump process.« less
  • The effects of the incidence angle of the main pump (MP) pulse in non-normal pumping geometry and the influence of the MP duration are investigated experimentally and theoretically for a transient collisionally pumped (TCE) x-ray laser in Ni-like Zr at 45 deg. and 72 deg. incidence angle on the target. The way they transfer to the x-ray laser output depends on the preplasma conditions, most notably on the average ionization distribution at the arrival of the MP. Moreover, contrary to previous grazing incidence pumping results, it is found that the shortest attainable MP maximizes the output. Modeling of the experimentalmore » results is performed with EHYBRID code. The results are important for scaling high repetition-rate non-normal incidence pumped lasers to sub-10 nm wavelengths.« less
  • A new x-ray laser mechanism is presented which uses radiation trapping of the strongest 3d {r_arrow} 2p neon-like resonance line in an optically thick plasma to create an intense radiation field which radiatively drives population from the neon-like ground state to the 3d state, which then lases to a pair of 3p states. Collisional mixing of the 3p states with nearby 3s and 3d states depopulates the lower laser states. Modeling is presented for this mechanism in neon-like argon. Strong gain is predicted on the two 3d {r_arrow} transitions at 45.1 nm and 46.5 nm, the first of which hasmore » been observed in recent x-ray laser experiments using an argon gas puff. The 3d {r_arrow} 3p line has also been observed at 60 and 30 nm, respectively, in x-ray laser experiments recently done on sulfur targets using the prepulse technique and on titanium targets driven by a nsed pulse followed by a psec pulse. This pumping mechanism also enhances the gain of the two 3p {r_arrow} 3s, J = O {r_arrow} 1 transitions which are at 43.1 and 46.9 nm in argon. This generic scheme can also work in other ionization stages. In nickel-like ions, the analogous process of lasing on the 4f {r_arrow} 4d transitions due to photo-pumping by the strong 4f {r_arrow} 3d lines will be discussed.« less