The effect of neutral nonresonant collisions on the shape, shift, and intensity of atomic spectral-line profiles is reviewed. A general treatment for the study of an atomic spectral line is developed by establishing reasonable assumptions about the relevant collision processes and by finding an expression for the Fourier transform of the line profile. The authors look at parallel developments of other methods of calculation, consider special limits of practical interest, and illustrate numerical evaluations of complete line profiles. Interatomic potentials for use in line-profile calculations are described, and the problems imposed by nonadditivity and nonadiabaticity are also noted. The observation of line profiles by both conventional and tunable-laser techniques is surveyed. Representative experimental measurements of the widths and shifts of collision-broadened spectral line cores are tabulated, and the phenomena of satellites, oscillations, and power-law behavior of line wings are compared with theoretical expectations. The use of experimental results for the determination of excited atom-atom interactions, the prediction of collision broadening in stellar atmospheres, and the effect of foreign gases on laboratory standard wavelengths are also discussed.

The effect of neutral nonresonant collisions on atomic spectral lines

A general nanosphere lithography (NSL) approach toward facile fabrication of free-standing, large-area, high-quality nanonets was developed, which was based on a floating colloidal crystal monolayer (CCM) mask at the gas/liquid interface for materials deposition via interfacial reactions. The hole size, spacing, and thickness of the highly ordered nanonets, which showed interesting photonic properties, can be readily adjusted. This NSL approach at the gas/liquid interface can be easily extended to fabricate large-area ordered nanonets of various metal sulfides, metals as well as inorganic minerals. Furthermore, a variety of ordered gold nanoarrays with unusual patterns were produced by using nanonet bilayers as unique deposition masks, suggesting that the obtained transferable, high-quality nanonets can function as versatile lithographic masks to generate novel nanopatterns.

Nanosphere Lithography at the Gas/Liquid Interface: A General Approach toward Free-Standing High-Quality Nanonets

Immersion gratings, diffraction gratings where the incident radiation strikes the grooves
while immersed in a dielectric medium, offer significant compactness and performance
advantages over front-surface gratings. These advantages become particularly large for
high-resolution spectroscopy in the near-IR. The production and
evaluation of immersion gratings produced by fabricating grooves in silicon substrates
using photolithographic patterning and anisotropic etching is described. The gratings produced under
this program accommodate beams up to
25 mm in diameter (grating areas to
55 mm×75 mm).
Several devices are complete with appropriate reflective and antireflection coatings.
All gratings were tested as front-surface devices as well as immersed gratings. The results of the
testing show that the echelles behave according to the predictions of the scalar
efficiency model and that tests done on front surfaces are in good agreement with tests
done in immersion. The relative efficiencies range from 59% to 75% at
632.8 nm. Tests of
fully completed devices in immersion show that the gratings have reached the level where
they compete with and, in some cases, exceed the performance of commercially available
conventional diffraction gratings (relative efficiencies up to 71%).
Several diffraction gratings on silicon substrates up to
75 mm in diameter having been produced, the
current state of the silicon grating technology is evaluated.

/pdf/production-and-evaluation-of-silicon-immersion-gratings-for-2cd65uwzh4.pdf

Production and evaluation of silicon immersion gratings for infrared astronomy.

Spectroscopic investigations of the structure of highly ionised atoms have undergone significant developments in recent years. The experimental progress is largely due to the introduction of several powerful light sources, such as laser-produced plasmas. Tokamaks and beams of fast, excited ions. The results obtained with these laboratory devices complement the data from astrophysical observations of the solar corona and solar flares. The experimental techniques are described in some detail. The results are discussed with respect to energy level studies along isoelectronic sequences, inner-shell excited levels, forbidden transitions, lifetimes and transition probabilities as well as the results of spectroscopic studies of quantum electrodynamics, QED. The experimental results are compared with theoretical predictions.

http://iopscience.iop.org/article/10.1088/0034-4885/52/2/002/pdf

The spectroscopy of highly ionised atoms

High harmonic generation of ultrafast laser pulses can be used to perform angle-resolved photoemission spectroscopy (ARPES) to map the electronic band structure of materials with femtosecond time resolution. However, currently it is difficult to reach high momenta with narrow energy resolution. Here, we combine a gas phase extreme ultraviolet (XUV) femtosecond light source, an XUV monochromator, and a time-of-flight electron analyzer to develop XUV-based time-resolved ARPES. Our technique can produce tunable photon energy between 24–33 eV with an unprecedented energy resolution of 30 meV and time resolution of 200 fs. This technique enables time-, energy- and momentum-resolved investigation of the nonequilibrium dynamics of electrons in materials with a full access to their first Brillouin zone. We evaluate the performance of this setup through exemplary measurements on various quantum materials, including WTe2, WSe2, TiSe2, and Bi2Sr2CaCu2O8+δ. Currently, it is difficult to reach high momenta with narrow energy resolution via laser-based angle-resolved photoemission spectroscopy (ARPES). Here, Sie et al. develop a time-resolved XUV based ARPES setup which can access the first Brillouin zone of all materials with narrow energy resolution.

/pdf/time-resolved-xuv-arpes-with-tunable-24-33-ev-laser-pulses-2neuqa85yt.pdf

Time-resolved XUV ARPES with tunable 24-33 eV laser pulses at 30 meV resolution.

Recent progress in the techniques of manufacture of spectroscopic diffraction gratings is described. Three main topics are discussed in detail; (i) the mechanical ruling of gratings, and the way in which the mechanical aspects of the ruling process affect the spectroscopic performance of the grating; (ii) the development of interference (or 'holographic') techniques for manufacturing gratings, and the relationship between ruled gratings and those made interferometrically; (iii) X-ray gratings for use at grazing incidence, and the different criteria that arise through the use of gratings in this way. The review was completed in April 1975.

https://iopscience.iop.org/article/10.1088/0034-4885/38/8/002/pdf

J F Verrill

Papers

Diffraction gratings (manufacture)