D. J. Nagel

Laser‐plasma interaction and ablative acceleration of thin foils at 1012–1015 W/cm2

The interaction physics and hydrodynamic motion of thin‐foil targets irradiated by long, low‐flux Nd‐laser pulses (3 nsec, 1012–1015 W/cm2) are studied experimentally and compared with theoretical models. Laser light absorption is high (80%–90%) and thin‐foil targets are accelerated up to 107 cm/sec with good (20%) hydrodynamic efficiency in the 1012–1013 W/cm2 range. These results agree with a simple rocket ablation model. Details of thermal heat flow, both axially (related to ablation depth) and laterally (related to beam uniformity requirements), are also presented.

Repetitively pulsed-plasma soft x-ray source.

A 10-Hz Nd:YAG laser system with 0.6-J, 25-nsec pulses was used to produce plasmas which emitted strongly in the soft x-ray region. Spectral, temporal, and spatial characteristics of these plasma emissions are presented together with an application of the source to soft x-ray lithography.

Laser‐produced‐plasma energy transport through plastic films

The transport of energy from a 1.06‐μm, 95‐psec laser pulse at an irradiance of 1015 W/cm2 through a thin layer of polystyrene into an Al substrate was studied by x‐ray, ion, and scattered‐light measurements. The intensities of the following quantities were measured as a function of polystyrene thickness: (1) x‐ray line radiation from the Al backing, (2) bremsstrahlung continuum from 3 to 88 keV, (3) ions of several keV energy, and (4) scattered laser light. The results indicate that a polystyrene thickness of no more than 0.5 μm is sufficient to inhibit substantial heating of the Al substrate.

The electronic properties of lamellar compounds of graphite — An introduction

Abstract A brief review is given of the electronic properties of the lamellar compounds of graphite, with particular emphasis on the dilute limit. Experimental methods of determining these properties are discussed and the applicability of a rigid band model with variable electrochemical potential considered. The role of the micro- and macro-scopic structure in determining properties is stressed. In this context, the change of conductivity with concentration of intercalant is used as an example of a property whose analysis depends sensitively on structure. Finally, a brief discussion is given of charge density waves, and a tentative mode for the intercalation process is outlined.

Quantitative x‐ray spectroscopy of neon Z‐pinch plasmas

Spatially resolved soft x‐ray spectra were collected for neon plasmas produced by imploding hollow annular gas puffs with MA level driving currents. The Z‐pinch imploded plasmas were studied for different risetime currents produced with or without the use of a plasma erosion opening switch (PEOS). Selected spectrograms were processed and analyzed to obtain absolute energies for the radiation emitted in the Ne ix and Ne x discrete transitions, as well as for total emission over the spectral range 900–1600 eV. The neon plasmas radiate 1–2.5 kJ in this energy range predominantly in the α transitions of both ions. The plasma uniformity inferred from spatially resolved spectral lines improves significantly using a faster rise‐time driving current.

Laser-Plasma Source For Pulsed X-Ray Lithography

The exposure of an x-ray resist by radiation from laser-heated plasmas was recently demonstrated. Single-shot submicrosecond exposures with a very favorable x-ray spectrum are possible. In order to reduce the cost of a laser-plasma x-ray lithography system, it is desirable to maximize the intensity in the soft (1 to about 3 keV) range. The x-ray output of laser-plasmas depends on laser pulse parameters (wavelength, pulse shape and energy), the focal conditions, and the target composition and geometry. Laser-plasma x-ray characteristics and their sensitivity to experimental parameters are reviewed in this paper. Presently available information indicates that a Nd:glass laser having pulse width in or near the 1-10 nsec range with at least 500 J of energy should be adequate for practical single-shot x-ray lithography.

Measurement of energy penetration depth of subpicosecond laser energy into solid density matter

The energy penetration depth characteristic of the interaction of intense subpicosecond (∼600 fs) ultraviolet (248 nm) laser radiation with solid density material has been experimentally determined. This was accomplished by using a series of ultraviolet transmitting targets consisting of a fused silica (SiO2) substrate coated with an 80–600 nm layer of MgF2. The measurement of He‐like and H‐like Si and Mg lines, as a function of MgF2 thickness, enabled the determination of the energy penetration depth. It was found that this depth falls in the range of 250–300 nm for a laser intensity of ∼3×1016 W/cm2. Based on numerical simulations, it is estimated that solid density material to a depth of ∼250 nm is heated to an electron temperature of ∼500 eV.

Plasma production from ultraviolet-transmitting targets using subpicosecond ultraviolet radiation

Plasma produced from ultraviolet-transmitting solid targets undergoing intense (>10(16) W/cm(2)) subpicosecond (~600 fs) ultraviolet (248 nm) irradiation have been studied under conditions for which no interfering prepulse plasma is generated. Time and spatially integrated measurements of the x-ray emission for H-like and He-like Mg and Si were found to be consistent with LASNEX calculations that model the laser-target interaction.

X-ray applications of self-scanning silicon diode arrays

A linear diode array consisting of 512 elements was used to measure soft x rays from laser-produced plasmas. Three modes of operation were tested, with the array behind (a) low-resolution filters, (b) a high-resolution spectrograph, and (c) a collimation device. The diode array used in this work has a higher fluence threshold, less dynamic range, and poorer spatial resolution at 2 ke V than Kodak No-Screen x-ray film. However, the immediate electronic readout characteristics of diode arrays make them attractive for some applications.

Component local densities of states for ordered TiNi

Densities of states for the ordered intermetallic compound TiNi, decomposed by site and symmetry, have been computed using the APW method. Of the fourteen valence electrons per unit cell, 7.2 were found to be in d like states localized on the Ni site. These results are useful for interpretation of the shapes and intensities of valence band X ray spectra.