P K Carroll

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 continua for absorption spectroscopy in the VUV and XUV

Recent work has shown that with appropriate targets, laser-produced plasmas provide clean essentially linefree continua suitable for absorption spectroscopy from 40 to 2000 A. A systematic study of the continua emitted by the elements from samarium to ytterbium is reported, and their use in absorption spectroscopy is demonstrated. The temporal profiles of the continuum pulses at different wavelengths are studied with a photomultiplier system and are found to have essentially the same halfwidths as the pulse from the exciting Q-switched ruby laser (~25 nsec). Pulse heights are shown to be reproducible to 15% or better. Ambient gases, at least at pressures up to several Torr, do not affect the emission mechanism. A comparison with other continuum sources at XUV wavelengths (i.e., BRV, synchrotron) is made, and possible future developments are outlined.

Spectra of Xe vii, viii, and ix in the extreme ultraviolet: 4d–mp, nf transitions

The spectrum of a laser-produced plasma of Xe has been photographed in the 40–220-A region. Many lines arising from the transitions 4d105s2–4d95s2mp, 5f, 4d105s–4d95s mp, 5f, and 4d10–4d9mp, 5f (m = 5, 6) in Xe vii, viii, and ix have been identified with the aid of Hartree–Fock calculations.

X-UV Absorption Spectroscopy with Laser-Produced Plasmas: A Review

Exteme-ultraviolet (X-UV) absorption spectroscopy has gained impetus in recent years, spurred on by a growing interest in the physics of core excited atomic, molecular and solid species. Progress in this field has been helped in no small measure by developments in X-UV light sources. One such source is the laser-produced plasma which, by suitable choice of target material, can be used to produce a clean, line free continuum virtually throughout the X-UV and V-UV spectral regions from 40-2000 ?. We briefly address here the issues surrounding the origin and characteristics of laser-plasma continuum light sources. In addition we review progress to date on the application of these sources to the study of the X-UV photoabsorption spectra of atoms, ions and molecules.

The B-X system of CF

The B-X system of CF has been observed in emission under high resolution and rotational analyses have been made of four bands. It is shown that the upper state is a regular 2 Delta state with coupling conditions approximating to Hunds case b. The spectroscopic constants derived for the B2 Delta state are T0=49341.4 cm-1, Delta G12/=1153-34, Be=1.3202, alpha e=0.0228, A0=0.76 or 4.48, gamma 0=-0.003. The potential curves for the X, A and B states are discussed and it is suggested that the B state mixes with a repulsive 2 Delta state from C(3P)+F(2P). Interpretation of this homogeneous perturbation in terms of potential curves leads to the conclusion that the curve for the B state goes to the limit C(3P)+F(2P) via a potential maximum. The A2 Sigma + state is considered as a Rydberg state with the electron configuration (1 pi )4(5 sigma )2( sigma 3s). The ionization potential is estimated to be 8.91 eV. The predissociation in the A2 Sigma + state is discussed and attributed to a quartet state, probably 4 Pi , from C(3P)+F(2P).

New continua for absorption spectroscopy from 40 to 2000 Å

The spectra of plasmas produced by focusing the output of a Q-switched ruby laser (output 1 J) on the rare-earth metals have been studied. From samarium (Z = 62) to ytterbium (Z = 70), strong quasi-uniform continua are emitted in the wavelength range 40–2000 A. Line emission from the target elements is absent over most of this wavelength region, particularly below about 600 A. The use of these continua as simple, reliable background sources for absorption spectroscopy in the vacuum-ultraviolet and soft x-ray region down to 40 A is demonstrated.

Rare-earth plasma light source for VUV applications

A compact versatile light source for producing VUV radiation from laser produced plasmas is described. Measurements of the spectral irradiance from CO(2) laser-produced plasmas on targets of gadolinium and ytterbium in the 115-220-nm range are given, and a comparison is made with analogous results obtained using a ruby laser.

Rotational studies of the Gaydon-Herman (green) bands of N2

The Gaydon-Herman green system of N2 has been studied under high resolution and rotational analyses made of the 0-0, 1-0, 2-1, 2-0 and 3-1 bands. It is shown that the transition involved is 3 Phi u-3 Delta g. The 3 Delta g state (which it is proposed to call G) shows essentially pure case b coupling and its fine structure can be interpreted in terms of spin-orbit and spin-spin interactions. The 3 Phi u state (called H) is inverted and close to case a at low J values. Its energy levels can be represented by the usual formulae for coupling intermediate between cases a and b to which a small correction must be added for spin-spin interaction and/or a singlet-triplet perturbation. Both states have relatively shallow potential curves and rather large equilibrium internuclear distances. From simple molecular orbital considerations it can be shown that both states arise by the simultaneous excitation of two valence-shell electrons, G 3 Delta g being derived from ...(1 pi u)2(3 sigma g)2(1 pi g)2 and H 3 Phi u from ...(1 pi u)3(3 sigma g)(1 pi g)2.

4s24p2-4s24p5s transitions in Ru XIII, Rh XIV and Pd XV

Spectra of ionised Ru, Rh and Pd have been observed in laser-produced plasmas. From these observations it has been possible to identify 4s24p2-4s24p5s transitions in Ru XIII, Rh XIV and Pd XV which lie near 100 AA in each of these elements.

Predissociation in the υ=13, 14, 15 and 16 levels of the B 3Πg state of N2: high resolution studies

The emission spectrum of the B 3 Pi g to A 3 Sigma u+ first positive system of N2 has been studied under high resolution to investigate the predissociation occurring in the B 3 Pi g state above the upsilon =12 level. The upsilon =13 and 14 levels are most strongly affected and detailed rotational analyses show that the process is not uniform and that in particular the 3 Pi 0- component of B 3 Pi g is predissociated only weakly and in a J-dependent manner. The predissociation is interpreted by correlating the levels of both the 3 Pi g state and the predissociating 5 Sigma g+ state with their equivalent states in the Hund case (c). The 3 Pi 0+, 3 Pi 1 and 3 Pi 2 components of the B 3 Pi g state are homogeneously ( Delta Omega =0), and hence relatively strongly predissociated by the Og+, 1g and 2g case (c) limiting equivalents of the 5 Sigma g+ state. The 3 Pi 0- component (Og- in case (c)) can be predissociated only by the 1g component of the 5 Sigma g+ state and hence the predissociation, being heterogeneous ( Delta Omega =+or-1), is relatively weak and J dependent. This interpretation fully explains the occurrence of transitions from the 3 Pi g- levels and their decrease in intensity with increasing J and is in keeping with the interpretation of analogous behaviour in the PH molecule.