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Atomic Physics Fundamental Constants Data Center High-Precision Laser Spectroscopy Fourier Transform Spectrometry Cold Atom Collisions and Quantum Information Theory for Nanoscale Systems and Metrologies Research on Highly Ionized Atoms High-Resolution X-Ray Diffraction and Scattering |
Division Contact: Wolfgang L. Wiese
Fundamental Constants Data Center The fundamental physical constants, such as the Rydberg, Planck, fine-structure, and Avogadro constants, are the links in the chain that bind all of science and technology together. Further, they can serve as the basis for improved practical representations of the International System of Units (SI) and thus for more accurate measurements of importance to both science and technology. The primary goal of the Fundamental Constants Data Center is to issue periodically a set of recommended values of the fundamental physical constants and basic conversion factors of physics and chemistry. This is accomplished by critically reviewing all data relevant to the constants that are available at a given epoch and analyzing it by a variety of methods, including least-squares. The resulting set of recommended values is distributed widely via archival journals, handbooks and reference books, textbooks, professional society magazines, and a web site. Because of the center's expertise in analyzing fundamental constants data, we are deeply involved in the worldwide effort to standardize the method of expressing uncertainty in measurement. To this end, we revise and publish NIST Technical Note 1297, Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results. Another principal task of the center is to serve as the NIST-authorized organization for the interpretation of the SI for use in the United States. As part of this task, we revise and periodically publish NIST Special Publication 811, Guide for the Use of the International System of Units (SI), and issue a Federal Register notice giving the official U.S. interpretation of the SI. Contact: Peter Mohr High-Precision Laser Spectroscopy Highly stabilized tunable lasers permit the investigation of atoms and molecules with a level of detail and precision that cannot be obtained with conventional spectroscopic techniques. Our work in this area ranges from observations of laser ionization of diatomic molecules in dense vapors to highly precise wavelength measurements that test the most advanced atomic theories for simple atoms. The high resolution provided by laser scanning permits studies of spectral line profiles, including pressure broadening, isotope shifts, and hyperfine structure. Sensitive detection techniques, including frequency and modulation and optogalvanic spectroscopy and use of thermionic diode detectors, permit observation of low concentration species in discharges and vapor cells. Typical applications of these data include wavelength standards, detection of trace elements in samples, and laser isotope separation. Facilities include stabilized lasers that are tunable from the near ultraviolet to near infrared and unique Fabry-Perot wave meter that is capable of real-time laser wavelength measurements with an accuracy of a few parts in 109. Contact: Craig
J. Sansonetti Fourier Transform Spectrometry High-resolution Fourier transform spectrometry allows the measurement of wide spectral regions with a precision unobtainable with grating spectrometry. This makes it ideally suited to the measurement of complex atomic spectra, where a spectrum of several thousand lines can be recorded with a wavelength precision of one part in 108 in less than an hour. Measurements of wavelengths, hyperfine structure, isotope shifts, and line intensity ratios can be made to high accuracy. The high-resolution Fourier transform spectrometer at NIST has a resolution of 0.0025 cm-1 and a wavelength range of 250 nanometers to 5.5 micrometers. Suitable sources have narrow spectral lines and include microwave discharges, hollow cathode lamps, and Penning discharges. Applications include the study of spectra of transition group and rare earth elements for astrophysics and the lighting industry. Contact: Craig J. Sansonetti return
to top of page We are developing computational and analytic models to describe collisional phenomena and atom-atom interactions in ultracold neutral atom traps. Atomic interactions play a crucial role in applications such as atomic clocks, Bose-Einstein condensates, and quantum information. The models are expected to be both quantitative and predictive and will be capable of describing collisions in optical or magnetic fields. Some specific application areas include photoassociation spectroscopy, magnetically tunable Feshbach resonances, clock shifts, cold molecule formation, and collisions in Bose-Einstein condensates. A promising new area of research is quantum logic using neutral atoms in optical lattices. This requires developing computational tools for collisions under conditions of tight trap confinement. Contact: Paul Julienne Theory for Nanoscale Systems and Metrologies As interest in nanotechnology grows, the need for accurate models for nanoscale systems and for the metrologies to characterize these systems becomes more critical. The NIST quantum processes group is establishing the theoretical approaches and computational tools needed to model complex quantum nanostructures. We have modeled T-shaped quantum wires, nanocrystallites, quantum-dot quantum wells, and coupled quantum nanostructures. Near-field optics has shown great promise for achieving subwavelength resolution in optical microscopy. We are developing a wide range of models and computational algorithms to define the metrological and imaging capability of near-field optics. We also are investigating nano-optical traps for holding cold atoms in the near-field of optical waveguide structures. Contact: Garnett Bryant We conduct comprehensive short-wavelength radiometry and optical materials characterization programs, including development and characterization of new ultraviolet (UV) and vacuum ultraviolet (VUV) sources and instrumentation. As part of this activity, we maintain a program to characterize and calibrate UV/VUV sources for calibrating UV/VUV instruments for industry, universities, and government laboratories, including NASA. We also collaborate directly with industry on programs to establish the UV and VUV optical properties of materials, including refractive indices and their wavelength, temperature, and stress dependencies. This work encompasses investigations of strain and defects that affect the optical properties. We develop and maintain state-of-the-art radiometric and spectroscopic facilities and new optical instrumentation, including UV/VUV interferometry, to support these investigations. Contact: John H. Burnett Research on Highly Ionized Atoms NIST's electron beam ion trap (EBIT) facility provides opportunities for researching atomic and plasma physics, ion beams, ion-trapping, laboratory astrophysics, ultrahigh vacuum scanning probe microscopy, and nanotechnology. Unlike conventional ion sources, the EBIT can produce ions of virtually any charge state from any species on the periodic table. Xe44+ (xenon with 44 of its 54 electrons removed) is easily produced in the NIST EBIT, for example. Ions are trapped radially and probed with a monoenergetic electron beam. Electrostatic end caps confine the ions axially. A large magnetic field is applied by a superconducting magnet to pinch the electron beam to high density and provide additional radial trapping. The carefully controlled conditions in EBIT allow scientists to unravel complex collision processes and measure photon spectra with very high accuracy. The ion temperature can be made to exceed 10 million degrees, or it can be lowered using evaporative cooling techniques. Several instruments are available to characterize and probe the trapped ions, including solid-state X-ray detectors, high-resolution X-ray crystal spectrometers, an X-ray quantum calorimeter, ultraviolet and visible grating spectrometers, and ccd cameras. An efficient ion extraction system for directing beams of highly charged ions onto surfaces is fully operational and equipped with an ultrahigh vacuum atomic force microscope and scanning tunneling microscope for in-situ studies of surfaces modified by collisions with highly charged ions. Applications that we hope to explore in the future include the formation of quantum dots, nanocrystals, and artificial cell membranes for biotechnology. Contact: John D. Gillaspy The properties of low-temperature plasmas play a key role in the processing of materials such as semiconductors. Proper characterization of these plasmas is essential to develop accurate plasma diagnostics and useful plasma models for specific applications. The use of diagnostics and models in the semiconductor manufacturing process is becoming increasingly important as additional control over plasma properties is necessary to continue the reduction of integrated circuit critical dimensions. We are conducting low-temperature plasma research on Gaseous Electronics Conference (GEC) radio frequency reference cells. These standardized plasma sources are designed to create plasmas similar to those found in commercial semiconductor plasma reactors, but with adequate access to the plasma for the development and use of different plasma diagnostics. Both capacitively and inductively coupled plasma sources are available for the production of low and high density plasmas. We are using or developing
a variety of different plasma diagnostics on the GEC radio frequency reference
cells at NIST. These include optical tomography, Langmuir probes, laser-induced
fluorescence, diode laser absorption, and submillimeter absorption spectroscopy.
These diagnostics are being developed for the understanding and control
of plasma uniformity, sheath dynamics, radical densities, pulsed plasmas,
and dual frequency plasmas. Reducing the thermal motion of atoms can lead to significant improvements in measurements and manifestations of the quantum nature of matter. Using radiation pressure from near-resonant laser beams, we can cool a gas of atoms to within a few microdegrees of absolute zero. These cold atoms can be trapped by laser beams and other electromagnetic fields. The temperature of the laser cooled atoms can be further reduced by evaporative cooling. At sufficiently low temperatures, the atoms undergo a quantum statistical phase transition called Bose-Einstein condensation in which the atoms accumulate in the lowest possible energy state. Such a sample of atoms, analogous to the source of photons from a laser, has unique coherence properties which can be exploited for improving measurements. Facilities for cooling and trapping atoms include continuous-wave dye, solid state, and semiconductor lasers. Atoms are trapped in laser, magneto-optical and magnetic traps. Sodium, rubidium, cesium, and xenon atoms are cooled, trapped, and used in such diverse applications as atomic-fountain frequency standards and studies of laser-modified chemical reactions. The Bose-Einstein condensate is being used as an intense and coherent source of atoms for atom interferometry and observation of non-linear matter-wave phenomena such as solitons and multiwave mixing. Contact: William D. Phillips High-Resolution X-Ray Diffraction and Scattering We can measure X-ray diffraction and scattering processes at high angular resolution using both double- and triple-axis measurement techniques. We perform double-axis X-ray diffraction analyses on a dedicated instrument with 0.5 microradian angular stepping precision. The double-axis diffractometer works in conjunction with an array of selectable incident beam monochromators to provide non-dispersive rocking curve analyses. We perform triple-axis measurements using a five-axis diffractometer working in conjunction with a 12 kW rotating anode X-ray generator. Both copper (0.154 nanometer X-ray wavelength) and silver (0.56 nanometer) anodes are available. The incident beam optics for this instrument include a set of crossed graded parabolic X-ray mirrors to provide a high X-ray flux in a small (less than 1 square millimeter) beam profile. A variety of post-mirror incident beam conditioning and post-sample analyzer crystals are available for the study of weakly diffracting structures such as protein crystals. The five-axis instrument also can be operated in a grazing-incidence surface diffraction mode for high-resolution X-ray diffraction analyses of ultrathin layered structures. Contact: Richard
J. Matyi For short-wavelength characterization of multilayer structures intended for larger wavelength X-ray optics, we have established a high-performance multiaxis X-ray reflectometer. This system provides highly collimated and monochromatic X-ray beams which, after reflection from the structure under study, can be examined for both specular and non-specular reflection characterization. The normal operating wavelength is 0.154 nanometer, and the on-scale reflectivity covers a range of six decades. The researchers also have a thin-film production facility capable of handling a wide variety of materials in the range of thicknesses from near one monolayer to a micrometer. The production process uses ion beam sputtering with simultaneous quasi-neutral beam milling to produce thin layers and synthetic multilayers of exceptional uniformity. These capabilities currently are being applied to the development and standardization of thin-film standards for the semiconductor industry. Contact: Richard
J. Matyi Applications of X-Ray Technology We have applied our experience with crystal diffraction techniques to the production, detection, and imaging of X-rays in support of space, semiconductor, spectroscopic plasma diagnostic, and medical applications. Tunable monochromatic X-ray sources and crystal spectrometers have been provided to perform pre-flight or post-flight calibration services to numerous NASA X-ray telescope missions. Curved crystal spectrometers also have been developed to measure the spectrum of X-rays emitted by the generators used in mammography. These spectrometers are used as a non-invasive calibration system since the high-energy endpoint of the spectrum is numerically equivalent to the applied voltage. Previously developed analysis tools also have been applied to assessment of wafer materials and homoepitaxial overlayers used in semiconductor processing. Capabilities include the design and construction of custom instrumentation and attendant data acquisition and control systems for the production and detection of X-rays, X-ray crystal preparation and characterization, and various X-ray spectroscopic applications. In addition, we maintain facilities to perform crystal lattice comparisons, X-ray topography, and digital imaging of X-rays. Contact: Larry
Hudson 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. We are working 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 allow robust control of the 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 currently are working toward measuring a displacement of up to 5 centimeters with 50-picometer resolution in a high-vacuum, vibration-controlled environment. Combining the optical techniques with simultaneous X-ray interferometry will allow us to perform a measurement of the lattice constant of silicon over a longer range than has ever been attempted. The program will address the metrology requirements of the semiconductor industry in the coming decade and have impacts in science in areas as diverse as gamma-ray spectroscopy and the realization of the kilogram using fundamental constants. Contact: John
Lawall
Date
created:
October 1, 2001 |