J. C. Moreno

Doppler-shifted line profiles from spherically expanding plasmas

We have performed high-resolution, extreme-ultraviolet spectroscopic measurements of both spherically expanding plasmas and planar-expanding plasmas, produced by using the Omega laser system in spherical illumination geometry and line-focus geometry. Direct comparison of spectral lines from these two types of plasma shows enhanced broadening of emission lines from the sperical plasmas. This broadening is attributed to Doppler shifts from large ion expansion velocities. A hydrodynamic code for laser-produced plasmas is used together with an atomic postprocessor to calculate output-line intensity profiles. Simulated line profiles are compared with experimental line profiles and show good agreement.

Identification of new Ti xxi and Ti xix transitions emitted by laser-produced plasmas

New spectral emission lines of Ti xxi and Ti xix have been observed and classified from a laser-produced plasma. The wavelength region for these lines is from 12 to 15 A.

Relative ion expansion velocity in laser-produced plasmas

The spectra of highly ionized titanium, Tixiii through Tixxi, and Cvi Lyman lines were excited in laser‐produced plasmas. The plasma was produced by uniformly irradiating spherical glass microballoons coated with thin layers of titanium and parylene. The 24‐beam Omega laser system produced short, 0.6 ns, and high intensity, 4×1014 W/cm,2 laser pulses at a wavelength of 351 nm. The measured wavelength for the 2p‐3s Tixiii resonance lines had an average shift of +0.023 A relative to the Cvi and Tixx spectral lines. No shift was found between the Cvi, Tixix, and Tixx lines. The shift is attributed to a Doppler effect, resulting from a difference of (2.6±0.2)×107 cm/s in the expansion velocities of Tixix and Tixx ions compared to Tixiii ions.

Identification of hydrogenlike and heliumlike transitions in the spectrum of laser-produced magnesium plasmas

Nonresonance spectral lines of Mg xii and Mg xi emitted by magnesium laser-produced plasmas have been observed in the extreme-vacuum-ultraviolet region and their transitions classified. As many as eight beams of the Omega laser system of the Laboratory for Laser Energetics at the University of Rochester were linearly focused onto magnesium-coated flat targets to produce linear plasma radiation sources from 3 to 6 mm long. The spectra were photographed end-on with a grazing-incidence spectrograph. The identified Mg xii lines are classified as 2s–3p, 2p–3d, 2s–4p, 2p–4d, and 3d–4f transitions. The identified Mg xi lines are classified as 1s2s–1s3p, 1s2p–1s3d, 1s2p–1s4d, 1s3p–1s4d, and 1s3d–1s4f. Ionization differentiation is based on comparing the present data with other magnesium spectra emitted from plasmas produced by different sources or differing in the ionization conditions. Transition classification is based on comparing the experimental wavelengths with the calculated values and studying the correlation between observed line intensities and the calculated oscillator strengths.

Thermal transport studies of 351-nm laser-produced plasmas using extreme ultraviolet spectroscopy

Spectra from an extreme ultraviolet (XUV) grazing incidence spectrograph have been used in the study of thermal transport in laser plasmas. These measurements with XUV lines allowed a diagnosis of much lower temperatures in the heating front than had been previously measured. The OMEGA (24‐beam, 351‐nm) laser system at the University of Rochester was used to produce plasmas from glass microballoons coated with Al or Ti substrates and overcoated with a plastic ablator. Thermal transport was investigated by measuring the intensity of x‐ray and XUV lines as a function of the thickness of the plastic overcoat. These measurements were then compared to the 1D hydrodynamic code lilac. Agreement between the hydrodynamic code and experiment could not be obtained with a reasonable value for the flux limiter ( f≤0.65). Consistent results were reached if nonuniform irradiation and flux inhibition is assumed. The measured burnthrough depths of around 9 μm are similar to previous measurements made with x‐ray lines at f...

Identification of new heliumlike Al XII transitions emitted by laser-produced plasmas

New spectral lines of Al xii, emitted by aluminum laser-produced plasmas, have been identified in the extreme-ultraviolet region and their transitions classified. As many as eight beams of the Omega laser system of the Laboratory for Laser Energetics at the University of Rochester were linearly focused onto aluminum-coated flat targets to produce linear plasma radiation sources from 3 to 6 mm long. The spectra were photographed edge-on, using a grazing-incidence spectrograph. The new lines are classified as 2s−3p, 2p−3d, 2p−4d, 3p−4d, and 3d−4f transitions. Ionization differentiation is based on comparing the present data with aluminum spectra obtained with other sources under different ionization conditions, while line identification is based on comparison with calculated wavelengths and oscillator strengths.

A spectroscopic study using line ratios of lithiumlike ions in a laser‐produced plasma

Spectra of highly ionized titanium and calcium in the extreme ultraviolet region were observed in laser‐produced plasmas using the OMEGA 24 beam (351 nm) laser system at the University of Rochester. The plasmas were produced using glass microballoon targets coated with a layer of a medium Z element and a layer of parylene (CH). Time‐integrated electron temperatures and densities were obtained by comparing measured line intensity ratios of lithiumlike charge states of Ti and Ca to numerical calculations from a collisional‐radiative model. The variation of line intensity ratios with electron density and temperature using the collisional‐radiative model is discussed.

Spectroscopic study of plasmas produced by a laser equipped with distributed phase plates

The spectra emitted by Al and Si laser-produced plasmas were recorded in the region of 18–350 A. The bandlike structures observed near the Al xi and Si xii 2p–3d transitions at 52 and 44 A, respectively, are identified as Be-like dielectronic satellite transitions in A1 and Si. The plasmas were produced with the Omega laser system at the Laboratory for Laser Energetics at the University of Rochester. Typical laser pulse lengths were 650 ps at a laser wavelength of 351 nm, with an intensity of 5–9 × 1014 W/cm2. The spherical targets employed in these experiments consisted of solid-glass spheres coated with a 2-μm layer of Al and an outer layer of parylene 0–8 μm thick, illuminated by 24 laser beams equipped with distributed phase plates (DPP’s) to improve the uniformity of illumination. The dielectronic transitions associated with the observed bands belong to the transition arrays 1s22pnl–1s23dnl, where n is the principal quantum number (greater than 2) and l is the azimuthal quantum number of the spectator electron. The observation of Be-like dielectronic transitions suggests that this emission occurs from a lower temperature (Te ≲ 100 eV) and higher density (Ne ≳ 8 × 1021 cm−3) plasma region. The influence of DPP’s on the emission of these dielectronic satellites is discussed.