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Current Directions

• Generation of Atomic Reference Data. We are producing atomic structure and collision data through innovative theoretical and experimental approaches, concentrating on neutral and low-ionization spectra but also covering highly ionized atoms of scientific and technological interest.

  On the theoretical side, we presently have in hand advanced atomic structure codes that produce reliable transition probabilities for strong transitions of light atoms (atomic number < 20). However, currently available theoretical methods do not produce data with high accuracy for moderately strong and weaker transitions. A new theoretical method based on non-orthogonal wave functions for individual bound electrons is being developed to introduce more many-body effects and eventually obtain more accurate transition probabilities for weaker transitions.

  A theory developed by us for the electron-impact ionization of atoms and molecules has provided reliable total ionization cross sections for molecules, molecular ions, molecular fragments and radicals. The theory has now produced very accurate cross sections for the helium atom that may be used as normalization standards for other calculations and experiments. The theory is being applied to atoms of interest in materials research and semiconductor fabrication, such as aluminum, chlorine, and germanium.

  On the experimental side, electron beam ion trap (EBIT) produces and traps ions in charge states up to 70+. With a combination of spectrometers, we measure transition wavelengths from the visible to the x-ray region. By observing the decay of metastable states, we directly obtain their lifetimes.

  With our ultra-high resolution Fourier Transform Spectrometer (FTS) and its greatly improved data acquisition system data acquisition system we have recorded spectra that are important for lighting industry applications, such as those of the rare earths Dy and Ho, as well as spectra of importance for astrophysics, such as those of Co and Ni.

  A new area of activity concerns spectral data for the rare gas elements. Although these data are needed for magnetic fusion research, astronomy, and industry, there is currently no unified source where they are conveniently available. In response to this need, we have started to work on a comprehensive tabulation to cover data for all the rare gases in all important stages of ionization. We are currently compiling data for neutral xenon and its ions. The work that has been carried out so far has revealed a pressing need for improved data for the rare gases in the infrared, and we are in the process of addressing this through new measurements with our high-resolution Fourier transform spectrometer. Because of the excellence of our FTS, we expect to obtain the best measurements ever made for the rare gases in this region.

• Data Compilations. Data centers on atomic spectroscopy located in the Division are the principal resources for spectroscopic reference data in the world community. We are continuing critical evaluations and compilations of wavelengths, atomic energy levels, and transition probabilities. The data assessment greatly benefits from our own atomic data research discussed above. We have put our data tabulations into a comprehensive atomic spectra database (Version 2) on the World Wide Web and will update and expand its coverage.

• Properties of Nanoscale Systems. Quantum mechanical and electromagnetic methods are being developed and applied for calculating the electronic and optical properties of quantum nanostructures and for modeling the optics of nanoscale objects. Such systems have a wide variety of technological applications, including semiconductor lasers and advanced semiconductor devices. Applications of nanooptics modeling include scanning near field optical microscopy for use in nanometer-scale optical metrology, and optical nanostructures for novel uses in atom trapping, quantum information and intradevice optical communications.

• Physics of Cold, Trapped Gases of Neutral Atoms. We are investigating, both experimentally and theoretically, the properties of cold dense gases in the quantum degenerate regime. We are using atom optics techniques to study the properties of Bose-Einstein condensates, and are developing such devices as an atom laser. The interactions between atoms strongly influence the properties of the condensate. Comprehensive, predictive theoretical models are being developed for the properties of such atomic interactions. The models are tested against experimental data on trapped atoms and provide critical data for modeling phenomena in Bose-Einstein condensation, atom optics, atomic clocks, and quantum logic. The nonlinear Schrödinger equation is used to predict properties of matter waves produced from a condensate.

• Quantum Information. We have initiated a new investigation on the possibility of using cooled and trapped neutral atoms in optical lattices as gates for quantum logic applications. An experimental effort is studying the loading of atoms into lattices from a Bose-Einstein condensate. A theoretical effort is developing simulation models of quantum gates to determine their fidelity in processing quantum information.

• Ion-Surface Interactions. With the NIST electron beam ion trap, EBIT, we make exotic, highly charged ions, which carry large amounts of potential energy, and we study the interactions of these ions with surfaces. Using a sample preparation system and an STM/AFM, which operate in ultra-high vacuum, we can prepare and characterize pristine crystalline surfaces in situ on an atomic scale. This allows us to identify and characterize nanoscale features, which are created by single highly charged ion impacts. We have been developing our expertise with this equipment and studying the features made in various surfaces upon highly charged ion impact.

• Plasma Measurements. The Division uses nonintrusive, optical emission measurement techniques to determine the properties of radio frequency (rf) inductively coupled and arc discharge plasmas. We are engaged in the detailed time- and space-resolved analysis of rf plasmas used in production-line plasma etching, and are also applying our experience in plasma work to develop and improve plasma radiometric source standards for the vacuum ultraviolet region.

• Optical Manipulation of Neutral Particles. We study the physics of laser cooling, electromagnetic trapping, and other radiative manipulation of neutral atoms and dielectric particles. We are using these fundamental studies to develop new kinds of physics measurements in areas such as high-resolution spectroscopy, atomic collisions, and atom optics aiming, for example, at improving atomic clocks.

• Optical Manipulation of Biological Objects. We are developing techniques for the remote manipulation of biological objects. We use laser trapping to manipulate cells, chromosomes and microspheres in order to study bio-molecular interactions. Applications of these investigations include fundamental studies of adhesion processes in biological systems, development of highly effective inhibitors of adhesion, very sensitive biosensors, and micromanipulation and microassembly.

• Precision Crystal, X-Ray, and Gamma-Ray Measurements. This work has three components: Optically-based measurements of a silicon lattice period (XROI); inter-crystal comparisons (delta-d); and Bragg-Laue diffraction studies using two-crystal instruments here and at the high flux reactor in Grenoble, France. XROI measurements are part of the new, sub-atomic displacement measurement project. Delta-d measurements are used to determine the lattice spacings of crystal samples used for x- and γ-ray diffraction, to compare crystal samples from the standards laboratories that are making absolute lattice spacing measurements (Germany, Italy, Japan), and to characterize the starting Si material for the Avogadro project. The joint NIST-ILL GAMS4 precision double crystal spectrometer at the Institut Laue-Langevin (ILL) measures γ-ray wavelengths on a scale consistent with optical wavelengths. These measurements are the basis for the most accurate γ-ray standards and lead to new, accurate determinations of the neutron mass, neutron binding energies, and atomic mass differences. At Gaithersburg, measurements to complement the x-ray wavelength tables project are made, using a second, two-crystal transmission spectrometer (high-Z region) and a vacuum spectrometer (energy region below 15 keV).

• High-Resolution X-Ray Probes of Geometrical and Electronic Structures. We have developed a high resolution x-ray toolset for the study of the electronic and geometrical structure of materials ranging from the most perfect silicon monocrystals through epitaxial layers, thin films and multilayer structures to surfaces and sub-surface damage in technical artifacts. Electronic structure questions are addressed by diverse spectroscopic techniques while the geometrical aspects are probed by several diffraction methods such as grazing incidence x-ray reflectrometry, scattering, and diffraction. Both areas are supported by a high performance Dual Ion Beam-Assisted Deposition capability for the production of reference quality multi-layer structures. In current applications of this work to semiconductor and magnetic storage technology, the goal is to delineate the structure in order to understand the effect of this meso-organization on materials and device performance. In the limit of highly perfect monocrystals, our interest is in the metrology of the remaining imperfection.

• Sub-Atomic Displacement Metrology. Linear displacement is a primitive component of many fundamental physical and technical measurements, yet its realization with atomic scale refinement and accuracy is difficult. Displacements are related to primary wavelength standards by interferometry, and at the moment the accuracy of interferometric measurements is at least two orders of magnitude below that of commercially available reference lasers. This project, which is a collaboration with the Manufacturing Engineering Laboratory and supported by competence funding, is aimed at improving the understanding and application of interferometry. The one-dimensional displacement of a specially fabricated translation stage will be simultaneously measured by means of heterodyne Michelson interferometry, scanning Fabry-Perot interferometry, and x-ray interferometry. This approach will reveal and provide a means of correcting for systematic errors that currently limit the accuracy of displacement measurements. The translation stage will be controlled in real time by closing a servo loop incorporating multiple Michelson interferometers. We are currently working towards measuring a displacement of up to 5 cm with 50 pm resolution in a high-vacuum, vibration-controlled environment.

• Core X-ray Diagnostics for Laser Fusion Plasmas. The division has been funded by the Laboratory for Laser Energetics and the Lawrence Livermore National Laboratory to design, manufacture, test, and field core-diagnostic x-ray spectrometer systems for respectively the OMEGA and NIF laser facilities. With the ultimate goal of validating high-performance direct drive fusion capsules, hard x-ray Bremsstrahlung spectra (12 keV to 60 keV) will be acquired in one laser shot. The results will be used to probe such issues as the electron temperature, density of the core plasma, and the hot electron energy distribution. To this end, we are producing curved-crystal spectrometers adapted from a design originally developed for the energy calibration of medical radiography x-ray sources.