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Future Directions

• Determination of Atomic Properties. We will continue to determine accurate structure data for those atoms and atomic ions that are of major interest in industrial and scientific applications, and we will utilize a variety of advanced experimental and theoretical approaches for this work.

  We will extend the capabilities for atomic physics research on highly charged ions from the EBIT with the addition of two instruments: a 1 m normal incidence spectrometer, and an x-ray microcalorimeter, which will be dedicated to the EBIT. With the normal incidence spectrometer we can access the full spectroscopic range from the visible to the VUV. The microcalorimeter combines high resolution with a high quantum efficiency response over a broad spectral range in the x-ray region, making it useful for a broad array of atomic reference data measurements. For example, we can use this instrument to study the cascade of atomic transitions that occurs as highly charged ions become neutralized in collisions with surfaces. Specifically, we will investigate the process of internal dielectronic recombination whereby an ion can emit L x rays, even if it originally had no vacancies in its L-shell.

  Our high resolution Fourier transform spectrometer will be used to observe spectra of complex atoms to measure wavelengths and branching ratios for transitions from the near UV to the far infrared. We are also starting efforts to operate the instrument as a user facility on a selective basis. As an initial effort, we will cooperate with astronomers to calibrate absorption wavelengths in iodine cells used for the detection of new planets with stars outside our solar system. In our high-precision laser spectroscopy facility, we are developing apparatus to carry out measurements for neutral lithium as an experimental check on new, highly accurate QED calculations.

  Work will continue to expand the range of our vacuum ultraviolet Fourier transform spectrometer to shorter wavelengths, with an ultimate goal to extend our capability for accurate wavelength metrology down to 110 nm. A new beamline for the Fourier transform spectrometer is being constructed at the SURF facility, a primary radiometric standard in the ultraviolet, which will enable us to carry out measurements of atomic branching fractions with very high accuracy.

• Critical Evaluation, Compilation and Dissemination of Atomic Data. Our critical data compilation work will proceed vigorously with new tabulations of spectroscopic data, i.e., wavelengths, energy levels, and transition probabilities, for elements of atomic numbers Z=1 through 36, and with updates and enlargements of our comprehensive spectroscopic database. Our new tabulations will contain more accurate as well as far more extensive data for each spectrum than the older NIST tables of the 1950s and 1960s, which are still the standard reference data works for a number of these elements. We will include the new compilations in our annually updated database on the Internet, the principal dissemination channel being the NIST Physics Laboratory Web Site. A new Handbook of Most Basic Atomic Data is being prepared for dissemination as an e-book as well as in hardcover format and on the web.

  Our multiyear effort to produce a new all-Z tabulation of x-ray wavelengths continues, and the currently available results will be soon disseminated electronically and in an archival journal. The electronic version of the x-ray wavelength table will be included in the Physics Laboratory Physical Reference Data web site. The extension of the calculations to the n=4 shell is almost complete except for corrections due to Auger and core-core interactions. For atomic numbers Z>50, the theory-experiment differences are particular large for transitions involving n=4 and thus need further clarification, requiring possibly new precision measurements.

• Nanoscale Systems. We are developing the large-scale computational techniques needed to study many-particle interacting quantum systems in complicated three dimensional geometries. We will complete our implementation of realistic tight-binding models for quantum dot nanostructures and extend these models to consider complex quantum dot architectures and hybrid quantum-dot/ molecular-electronics nanosystems. Novel optical and photonic properties are expected for these complex nanosystems. We will model the properties of these nanosystems to identify their uses in enhanced optoelectronic devices, quantum optics, classical and quantum information processing.

  Having developed our expertise with STM and AFM and having demonstrated their usefulness for imaging surface defects in graphite and mica, we now plan to deploy both of these techniques on the more technologically important surfaces of silicon and silicon dioxide. In this way, we will study the nanoscale features created by highly charged ion bombardment in an ultrahigh vacuum environment.

  In the thin film area, we plan to move toward more robust modeling of complex layer structures using wavelet analysis. The wavelet approach provides not only density and thickness estimates, but also layer roughness and diffusion information. Our existing thin film diffractometer will be upgraded with improved front-end optics and angle measuring encoders. Additional new experimental capabilities will include a multipurpose high intensity diffraction system consisting of a rotating anode x-ray generator and a five circle diffractometer and a high resolution diffractometer/reflectrometer for in situ monitoring of chemical vapor deposition growth by real-time x-ray diffraction, reflection, and fluorescence. These additions will further expand the x-ray toolkit that will be available for semiconductor manufacturing problems. The growing appreciation and acceptance of x-ray measurement techniques in thin film and multilayer metrology encourages us to focus on this growth-oriented area. We plan to continue our efforts to establish collaborations with the microelectronics industry and seek additional support for the capabilities we are developing.

  Near-field optical microscopy shows great promise for achieving subwavelength optical resolution. Theoretical models of NSOM images are essential to utilize NSOM for nanoscale metrology. Our computational tools to model and interpret NSOM images, including finite difference and element approaches, mode expansion and scattering techniques, will be integrated into a general computational package to best exploit each technique. Specific applications will focus on apertureless NSOM for enhanced resolution, diagnostic imaging for optical waveguides, and local nanoscale engineering of optical waveguides and photonic crystals. Nanooptics modeling of optical nanostructures will continue to identify and engineer structures optimal for use in quantum computing and local, intradevice optical communication.

• Laser Cooling and Atomic Manipulations. We plan to investigate the photoassociation process in a BEC and compare it to the equivalent transition for atoms in a magneto-optical trap. We will also compare absolute rates observed with the current theories of photoassociation in traps and condensates and try to resolve some discrepancies between several current predictions. In addition, we plan to investigate coherent ground-state molecule formation in a condensate and study the possibility of using optically-induced Feshbach resonances to alter the scattering length in a BEC. In conjunction with our work in quantum information, we will continue to study BECs loaded into periodic potentials (optical lattices).

  We will study the interplay between tunneling and atom–atom repulsion and the effects on the phase coherence between wells. We will investigate the effects of reduced dimensionality on the collision properties and the condensate properties.

  We will study the energy balance conditions of ultracold plasmas, and investigate three-body recombination and other processes that lead to the formation of bound atoms. Such processes are required to account for the excess energy observed in plasma expansion experiments. Recombination at these low temperatures has never been measured, and the usual theory is expected to be inapplicable.

  We will investigate collisions, in particular photoassociative collisions, in a magnetic trap and pursue our study of time-resolved collisions. Performing these experiments in a new experimental chamber that will be capable of ion detection from a spin-polarized sample in a magnetic trap will enable us to relate the measurements to the theoretical predictions much more closely. We hope to quantify the differences between the collisions in a cold but free gas and those that take place in the tight confining potentials of optical lattices or Bose condensates.

  Quantitative predictive models of atom interactions in cold atomic gases and Bose-Einstein condensates will be refined and applied to Bose-Einstein condensates, collisional shifts in atomic clocks, cold molecule production, and quantum computing using neutral atom optical lattices. We will continue to develop methods for characterizing matter waves and atom lasers derived from Bose-Einstein condensate sources.

  The optical tweezers team will continue to study the time scales of bio-adhesion, using antibodies and antigens and neutrophil systems. Adhesion in these biological systems is relevant to such issues as the immune response and cancer metastasis.

  The study of phospholipid vesicles will also be the focus of our biophysical project, in which the optical tweezers will be complemented by a new optical scissors setup. The vesicles, also known as liposomes, are important for pharmaceutical applications such as the development of drug delivery systems and the controlled release of the encapsulated drugs inside the body. In a joint effort with the analytical chemistry division we plan to develop a "laboratory on a chip" based on microfluidic channel arrays and manipulation of vesicles as synthetic cellular environments.

• Quantum Information. We are developing a program in quantum information processing that will investigate the use of neutral atoms loaded in optical lattices and other trap arrays. We are constructing a new laboratory apparatus that will slow and trap ⁸⁷Rb atoms in a laser trap. We will transfer the atoms to a magnetic trap and evaporatively cool them to form a BEC. We plan to load the BEC into the ground vibrational states of various dimensional optical lattices, formed with intersecting beams of light, for manipulation. The movement of some of the trapped states with respect to others will allow us to investigate controlled collisions or, in other words, controlled phase shifts of some of the atoms. We hope to use such controlled phase shifts as quantum phase gates in quantum information processing. One of the first experiments we hope to pursue is the study of an analogy to the Mott insulator transition in the atoms for the optical lattice.

  As a part of the new NIST Quantum Information Program, we will provide realistic simulation models for quantum logic gates implemented with neutral atoms in optical lattices. Such gates will provide the basis for implementation of quantum communication or computing devices. The simulation models will provide guidance and understanding for the experimental implementation of such gates by the Laser Cooling Group and aid in optimizing their performance. The initial task is to assess the viability and gate fidelity for a number of proposed schemes for realizing such gates. The long term goal is to produce quantitative, predictive models of the coherent quantum dynamics for realistic gates.

• Metrology. We will extend our investigations of two-dimensional Raman cooling of cesium atoms launched in a fountain geometry, to include sideband cooling in an optical lattice, for possible future implementation in space-based laser cooled atomic clocks. We will study the prospects for adiabatic expansion and delta-kick cooling of a condensate or evaporatively cooled sample for possible space clock applications.

  Our efforts in displacement metrology will be concentrated in the sub-atomic displacement metrology project, which is developing a measurement system integrating heterodyne Michelson interferometry, Fabry-Perot interferometry, and x-ray interferometry. Our immediate future direction in this project is the measurement of a displacement up to 5 cm using real-time control of all six degrees of freedom. Simultaneously, the range of the displacement measurements is being extended from 5 cm to 100 cm with strong input from MEL in this joint competence project.

  We are investigating the use of mode-locked femtosecond laser systems for interferometric displacement measurement; these systems seem to offer the possibility of improved accuracy and speed and a direct link to the definition of the length standard. Other potential uses relevant to the activities of our group are the creation of soft x-rays via high harmonic generation and studies of materials exploiting time-resolved x-ray diffraction.

• DUV Materials Characterization. An important set of materials parameters needed for the design of the optics for 157 nm lithography systems are the 157 nm stress-optical coefficients and their dispersions. These parameters characterize the effects of stress on the index properties and have never been measured in the UV. We have begun a program to determine these values for all the principal optical materials being considered for 157 nm lithography optics, including calcium fluoride, barium fluoride, lithium fluoride, and VUV-grade (vacuum-ultraviolet) modified fused silica. This project involves making a first-of-its-kind VUV Twyman-Green interferometer, which will operate down to below 150 nm.

  Our VUV interferometer is designed to have phase-shifting and spatially resolving capabilities. This will enable us to obtain spatial phase shift maps of materials, from which we will be able to extract the index inhomogeneity and birefringence properties of the materials for wavelengths from the visible down to the VUV. These properties have never been measured in the VUV and are needed to evaluate materials to be used in the optics of 157 nm lithography systems.

  Our VUV Fourier transform spectrometer will be installed at a dedicated beamline at NIST's SURF facility. The high intensity of the synchrotron radiation will facilitate effective measurements of the refractive index and dispersion of UV optical materials.

• Process Control of Industrial Plasmas. Optical diagnostic methods will continue to be developed for potential process monitoring and control of industrial plasmas. Optical tomography sensors, IR laser absorption, sub-mm wave absorption and other diagnostics will be investigated as potential process control parameters of plasma uniformity or radical species densities. Additional plasma measurements will be attempted on the GEC RF Reference Cell to resolve issues related to temperature gradients, plasma surface interactions and ion molecule reactions which are important to plasma modeling and the implementation of commercial plasma process control systems.