James H. Scofield

Relativistic hartree-slater values for K and L X-ray emission rates*

The x-ray emission rates for the filling of K - and L -shell vacancies, calculated with the relativistic Hartree-Slater theory, are given for elements with Z =5 to 104. Account was taken of the finite extent of nuclear-charge distributions. Presented are ratios of the major K -shell components, the total K - and L -shell radiative decay rates, and the rates of emission of individual x-ray lines.

X-ray attenuation cross sections for energies 100 eV to 100 keV and elements Z = 1 to Z = 92

This work presents for the energy range 0.1--100 keV the National Bureau of Standards (NBS) database of experimental x-ray attenuation coefficients (total absorption cross sections) and cross sections calculated using a relativistic Hartree--Slater model for the photoelectric cross section for all elements of atomic number Z = 1--92. The information is displayed in both tabular and graphical form. Also shown on the graphs are cross sections obtained using the semiempirical set of recommended values of B. L. Henke and co-workers (Atomic Data and Nuclear Data Tables 27, 1 (1982)). A bibliography of the NBS database for this energy range is included. copyright 1988 Academic Press, Inc.

The use of an electron beam ion trap in the study of highly charged ions

The Electron Beam Ion Trap (EBIT) is a relatively new tool for the study of highly charged ions. Its development has led to a variety of new experimental opportunities; measurements have been performed with EBITs using techniques impossible with conventional ion sources or storage rings. In this paper, I will highlight the various experimental techniques we have developed and the results we have obtained using the EBIT and higher-energy Super-EBIT built at the Lawrence Livermore National Laboratory.

Short wavelength x-ray laser research at the Lawrence Livermore National Laboratory*

Laboratory x‐ray lasers are currently being studied by researchers worldwide. This paper reviews some of the recent work carried out at Lawrence Livermore National Laboratory. Laser action has been demonstrated at wavelengths as short as 35.6 A while saturation of the small signal gain has been observed with longer wavelength schemes. Some of the most successful schemes to date have been collisionally pumped x‐ray lasers that use the thermal electron distribution within a laser‐produced plasma to excite electrons from closed shells in neon‐ and nickel‐like ions to metastable levels in the next shell. Attempts to quantify and improve the longitudinal and transverse coherence of collisionally pumped x‐ray lasers are motivated by the desire to produce sources for specific applications. Toward this goal there is a large effort underway to enhance the power output of the Ni‐like Ta x‐ray laser at 44.83 A as a source for x‐ray imaging of live cells. Improving the efficiency of x‐ray lasers in order to produce s...

X-ray laser research at the Lawrence Livermore National Laboratory Nova laser facility

We describe our optical-laser-pumped x-ray laser program. Our long-term goal is to develop and utilize a fully coherent, gigowatt-power-level sub-44-A laser. To this end we have been studying the characteristics of the exploding-foil amplifier coupled with various inversion schemes: Ne-like and Ni-like collisional excitation as well as H-like three-body recombination. Most of our experimental results to date are for the Ne-like schemes; we have observed ~15 laser transitions in Se, Y, and Mo having wavelengths from 26.3 to 10.6 nm. Output power to at least 1 MW has been observed for the Se J = 2 to 1 lines at 20.6 and 20.9 A along with geometrical divergence patterns for the beam. We have also observed time-dependent beam refraction from these amplifiers and have been able to demonstrate double-pass amplification by using a multilayer mirror operated at normal incidence. Future plans for improving beam coherence and producing lasing at wavelengths shorter than 44 A are discussed.

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.

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.

Wavelengths of neon-like 3p → 3s X-ray laser transitions

This paper presents the wavelengths of the neon-like 3p → 3s laser lines which have been observed in both lasing and nonlasing plasmas and compares the experimental wavelengths with relativistic multi-configuration Hartree-Fock calculations in order to estimate the wavelengths for these lines in all neon-like ions between S6+ and Xe44+. The seven 3p → 3s transitions which have been observed to lase in some neon-like ions are considered in this work.

Simulating a Maxwellian plasma using an electron beam ion trap

We describe a technique for producing a Maxwell–Boltzmann electron energy distribution using an electron beam ion trap (EBIT). The technique was implemented on the Lawrence Livermore EBIT to simulate Maxwellian plasmas. We discuss technical and experimental issues related to these simulations. To verify the fidelity of the quasi-Maxwellian, we have measured line emission due to dielectronic recombination (DR) and electron impact excitation (EIE) of heliumlike neon, magnesium, and argon for a range of simulated electron temperatures. The ratio of DR to EIE lines in heliumlike ions is a well understood electron temperature diagnostic. The spectroscopically inferred quasi-Maxwellian temperatures are in excellent agreement with the simulated temperatures.

Reinvestigating the early resonantly photopumped x-ray laser schemes.

Although H and He-like resonantly photopumped laser schemes were among the earliest methods proposed for producing x-ray lasers, demonstrating these schemes in the laboratory has proved to be elusive. Nevertheless the resonantly photopumped schemes remain interesting both because of their potential to improve the efficiency of lasers that otherwise operate through other process such as recombination and because of their potential for yielding entirely new and relatively efficient lasers. We present an expanded list of candidate lasers that operate by utilizing Ly-alpha or He-alpha radiation from a pump ion to photopump an electron from the ground state of a H or He-like lasant ion to the n = 3 or 4 state, with subsequent lasing between the n = 4 ? n = 3 or n = 3 ? n = 2 states of the H or He-like ion. The example of the potassium-pumped chlorine scheme, which exhibits both 4 ? 3 and 3 ? 2 laser lines, has been modeled extensively, and the results of the calculation are presented.