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1 ~ Physics Laboratory: Division Reviews ELECTRON AND OPTICAL PHYSICS DIVISION Technical Merit The Electron and Optical Physics Division develops measurement capabilities needed by emerging electronic and optical technologies, especially those required for submicrometer fabrication, character- ization, and analysis. The division consists of three groups: Photon Physics, Far UV Physics, and Electron Physics. During its assessment the panel found that the technical quality of the division's work continued at a very high level, leading to important advances in several areas. Discussion of the technical quality of ongoing work for each of the groups is presented below. Photon Physics The Synchrotron Ultraviolet Radiation Facility (SURF III) has now been operational for a year since its most recent upgrade. Emphasis has been placed on work in the extreme ultraviolet (EUV) spectral region. Because of the ready availability of stable, debris-free radiation in this wavelength range, the SURF III facility is well suited for this work. Such work is of major importance to the semiconductor community, since EUV lithography is the leading candidate for next-generation lithography technology. This past year, the group participated in an EUV mirror reflectometry study that compared the measurement results from five different facilities. It was found that the NIST EUV monochromator exhibits poor wavelength control owing to mechanical instabilities. An upgrade has been initiated for this monochromator at a cost of approximately $250,000. This expense is justified, since EUV mirror NOTE: Chapter 5, "Physics Laboratory," which presents the laboratory-level review, includes a chart showing the laboratory's organizational structure (Figure 5.1) and a table indicating its sources of funding (Table 5.1~. 175
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176 AN ASSESSMENT OF THE NIST MEASUREMENT AND STANDARDS LABORATORIES: FY 2003 testing will continue to be an important function provided by NIST as the EUV lithography market begins to grow. Once this capital improvement is complete, NIST should be in a position to provide this measurement service, for a fee, to industry. A second important characteristic of EUV mirrors is their lifetime under exposure. At the beginning of last year, an EUV mirror lifetime test capability was being constructed. At that time it was suggested by the review panel that NIST pursue funding for this lifetime testing, since its facility was uniquely qualified for such long-term lifetime testing under controlled conditions. It has done so and received some nominal fees from parties interested in improving the reflectivity lifetime of EUV mirrors. This lifetime testing is very critical to the success of the EUV lithography market. This work should be continued and expanded, and additional external funding should be pursued. Another area of strength for the Photon Physics Group is in the calibration of EUV detectors. Understanding not only the performance of EUV detectors, but also the entire method and apparatus for selecting out the 1 3.5-nm radiation band of interest for lithography is important for this industry. At the present time, many different methods are used to select the desired 13.5-nm radiation for measurement. Each method has its strengths and weaknesses. Understanding these issues and providing this informa- tion to the EUV lithography community fit well within the NIST charter. In addition, NIST can provide the neutral-party evaluation of these methods that is needed for improving the ability to compare results from different EUV source vendors and users. The Photon Physics Group made progress during the past year toward creating a world-class EUV radiation facility. Knowledge of this group's capabilities among researchers in the field, both at public institutions and in private industry, should be promoted more aggressively. Far UV Physics The Far UV Physics Group operates, maintains, and continues to improve the SURF III synchrotron light source. Activities at SURF III are becoming more and more focused on radiometry in the ultravio- let, serving the lithography community. As the critical dimensions of electronic devices become shorter, the wavelengths required for lithography move into the UV and EUV, such as the laser lines at 193 nm and 157 rim and the multilayer EUV wavelength of 13 nm. SURF III can play a unique role in the United States by providing an absolute calibration standard for these wavelengths. Comparison measurements have been made at similar institutions abroad, such as the Physikalisch-Technische Bundesanstalt in Germany. At present, U.S. researchers are sending their detectors to these foreign laboratories for calibration. This NIST facility is equally qualified for such work and should pursue all practical oppor- "unities. The facility and its beam lines have undergone a continuous series of upgrades and are now better by far than originally designed. A new beam line has become operational (Beam line 3), providing an absolute radiation standard by tracing the light intensity to that of a single electron, which is calculable from first principles. An array of photodiodes brackets the large dynamic range between few electrons and a normal beam current (up to 1 A, an increase by an order of magnitude over the past few years and an amazing feat for such a low- energy storage ring). A second radiometry beam line features a cryogenic detector that provides an absolute standard for detectors (Beam line 4~. A widely used product is the calibration of diodes as secondary standards, which entails painstaking measurements of aging effects and development of diode coatings, such as platinum silicide, for better stability. A UV interferometer beam line is also serving the lithography community by high-precision mea- surements of optical constants. These are required for the demanding specifications of CaF2 optics for
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PHYSICS LABORATORY: DIVISION REVIEWS 177 excimer laser lithography. Measurements are under way that are relevant to immersion lenses, which might be able to extend the use of optical lithography by one more device generation. On the machine side, an RF upgrade has now been completed that provides a stable beam up to the full current of 1 A and a high degree of control over the beam shape and lifetime. A donated photoelectron microscope is currently being retrofitted and tested with a UV lamp. It allows imaging of the work function distribution across a surface. It has been used previously for imaging chemical reactions at surfaces. It would be interesting to explore whether this technique can be used for imaging radiation damage on diodes and optical elements. Owing to its low beam energy, SURF III is well suited for providing photons with energies in the typical range of work functions (3 to 5 eV). Electron Physics the Llectron Physics Group is an internationally recognized leader in the development of innova- tive measurement tools and techniques, harnessing them to address fundamental challenges at the forefront of nanoscale science and technology. The Nanoscale Physics Laboratory constructed by the group is composed of a scanning tunneling microscope (STM) combined with two molecular beam epitaxy units and a field ion microscope for tip preparation. A fixed-direction magnetic field as large as 10 tesla (T) or a variable-orientation field up to 1.5 T can be applied to a sample. The system can operate at temperatures as low as 2 K. This unique facility will enable the group to maintain its leadership position in the synthesis and characterization of nanostructured materials. Recent research includes the first real-space measurement of the magnetic field-induced hexagonal-to-square transition in the vortex lattice structure of the superconducting compound V3Si. Work is also proceeding on the autonomous atom assembly project mentioned in last year's report. The goal is atom-by-atom fabrication of quantum structures. Current attention is directed toward perfecting the control software and optimizing the parameters for tunneling manipulation. Significant progress has been made in the "atom on demand" effort, which involves capturing single atoms in a magneto-optical trap and moving them with lasers. A high-power CO2 laser has been acquired for use as "tweezers" to extract atoms from the source. The next steps are to assess the viability of this approach and then to place atoms into specific magnetic traps. One tantalizing objective is to create architectures for quantum computing. As reported last year, one goal of the Scanning Electron Microscopy with Polarization Analysis (SEMPA) project is 10-nm image resolution of magnetic structures such as hard disk storage media. Although the field emission scanning electron microscope acquired for this purpose continues to func- tion at 25-nm resolution, attainment of the 10-nm scale remains elusive because of the vendor's inability to meet specifications. The existing capability is being used to image various patterned nanostructures and to investigate the behavior of thin magnetic films (e.g., Fe on a GaAs substrate). Additionally, work with the Naval Research Laboratory (NRL) is being initiated to analyze real-time operation of spintronic devices such as sensors. A theoretical effort effectively complements the experimental work of the Electron Physics Group by serving as a catalyst for new ideas and providing a valuable resource for problem solving. Internal as well as external interactions have been established. An example of the former is analytical work on vortex states in V3Si to assist the Nanoscale Physics Laboratory's measurements, while among the latter are a collaboration with Nanoscale Physics Laboratory on spin injection from a ferromagnetic metal into a semiconductor and work with researchers at the Georgia Institute of Technolo~v and the Johns Hopkins University addressing spin-transfer torques in magnetic heterostructures. A,
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178 AN ASSESSMENT OF THE NIST MEASUREMENT AND STANDARDS LABORATORIES: FY 2003 Program Relevance and Effectiveness A wide variety of organizations have great interest in the expertise and capabilities of the Electron and Optical Physics Division. Customers of the Photon Physics and Far UV Physics Groups include corporations as well as government agencies and laboratories that need calibration standards for radiom- etry. Typical products are diodes as secondary standards; calibration of the exposure of photoresists, which becomes more and more critical with high-contrast resists; calibration of (multilayer) optics; and calibration of charge-coupled detectors. The ongoing, cutting-edge research of the Electron Physics Group in nanoscale science and technol- ogy is relevant to a broad spectrum of industrial, academic, and government customers. Many compa- nies await the high-resolution SEMPA capability being pursued in the group. The Nanoscale Physics Laboratory will undoubtedly stimulate customer interest in several areas, such as single-atom manipula- tion for device structure fabrication and quantum computing. The "atom on demand" work has potential applications in quantum information processing and modulated doping. Technical results are communicated to customers in various ways among them, direct interac- tions, presentations at conferences, and reports. Division researchers continue to publish a significant number of high-quality papers in the refereed scientific literature, satisfying the panel's expectation in the previous report. The panel strongly encourages the division to maintain this important form of participation in the activities of the external scientific community. Division Resources The panel is concerned that funding for overhead functions in the Electron and Optical Physics Division seems to be getting more limited. It is recognized, however, that many of the limitations were created by external mandates imposed after the terrorist attacks of September 11, 2001. Significant start- un problems with the use of electronic forms (e.~.. nav for performance) were also noted bv the staff. --r r- - - ------ ---- ---- --- - - - --- - -- - ---- - ------ x- -o-7 r --a - -- r --- ---------- -a -- - ---- - --- -- -- - ~ ---- - ------ ~ . . . . . , . , , , ^^ , , , . . , , . ,, , an, L,lvlslon morale remains nlgn, and staid members shared in several awards during the past year. -l-ne recent Nobel Prizes won by NIST scientists continue to stimulate intellectual excitement and enthusi- asm. ATOMIC PHYSICS DIVISION Technical Merit The Atomic Physics Division develops and applies atomic physics research methods to achieve fundamental advances in measurement science and to produce and critically compile physical reference data. The division is organized in five groups: Plasma Radiation, Quantum Processes, Laser Cooling and Trapping, Atomic Spectroscopy, and Quantum Metrology. The panel is very favorably impressed with the excellent performance of the division in achieving its mission. The following subsections provide examples of ongoing work in each group and present discussions illustrating its quality and high level of importance to scientific and industrial communities. Plasma Radiation Among other things, the Plasma Radiation Group operates the laboratory's electron-beam ion trap (EBIT). The NIST EBIT is a unique, well-characterized facility that allows fundamental studies of a
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PHYSICS LABORATORY: DIVISION REVIEWS 179 variety of processes with highly charged ions for both fundamental science and its applications. This facility allows studies that make unique and important contributions on a wide variety of topics, and the group continues to be a leader in studies of the fundamental properties of highly charged ions. The EBIT effort is divided into two parts: in-trap studies (UV/X-ray spectroscopy) and surface studies. Of particular note this year are the charge exchange studies that the group performed using its new gas jet target. The group's expertise in surface modification by highly charged ions has led to its playing a pivotal role in the characterization of damage to light-collection optics for EUV lithography by highly charged xenon ions. The group is also successfully pursuing properties of optical materials at the 157-nm wavelength using optical measurements. These properties are of importance to future-generation vacuum ultraviolet (VUV) lithography for integrated circuits. The group not only has discovered the original birefringence phenomenon but also has generated the new concepts that are required for the development of new hybrid materials, to avoid the problem. This effort has resulted in substantial outside recognition for the Physics Laboratory. The Gaseous Electronics Conference (GEC) reference cell work on submillimeter spectroscopy of processing plasmas is demonstrating its importance for understanding the influence of important trace components in mixtures at very low concentrations. Quantum Processes The Quantum Processes Group is one of the few theoretical atomic, molecular, and optical (AMO) physics groups in the United States; as such, it is a national resource and leader in the U.S. theoretical AMO community. Theoretical advances of the group support a variety of experimental efforts, such as clocks, quantum degenerate gases, quantum dots, single-molecule detection, and quantum information. A distinguishing mark of the group is its emphasis on realistic models of the processes it is studying, and for this reason it is often able to confront experimental information in meaningful ways. Over the years, the group has developed a number of numerical codes and successfully applied them to a wide variety of physical, chemical, and optical phenomena. It plays an important leadership role in the NIST Quan- tum Information initiative. The Quantum Processes Group is very productive and has made a number of significant advances during the past year. Examples of note to the panel are the recent demonstration of Bose condensate in Cs gas, new work on coherent manipulation of collisions in Bose-Einstein condensates (BECs) that permits new insights into the production of ultracold molecules, and new concepts for neutral-atom quantum computing. The group continues to supply absolutely essential theoretical support for many activities of the Laser Cooling Group and is advancing the state of the art of simulation of quantum dots. Laser Cooling and Trapping The Laser Cooling and Trapping Group is pursuing a large number of cutting-edge experiments in atomic and quantum physics. Experiments under way include a variety of experiments on Na and Rb BECs, in particular, studies of superlattices that are proving to be extremely interesting and fruitful. Other experiments include studies of ultracold photoassociation in coherent and incoherent atomic samples as well as studies of ultracold plasmas that are leading the field. The group is internationally recognized for its excellence and leadership in an extremely competitive and productive field of re- search. It is a national treasure that should continue to be nurtured by NIST.
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180 Atomic Spectroscopy AN ASSESSMENT OF THE NIST MEASUREMENT AND STANDARDS LABORATORIES: FY 2003 The Atomic Spectroscopy Group is the primary center in the world for critically evaluating, compil- ing, and disseminating basic atomic spectroscopic data as well as fundamental physical constants. It also provides highly accurate laboratory measurements and theoretical computational tools in response to the individual needs of customers who commission such work. The work done to meet such customer needs often leads to improvements in knowledge of the structure and spectroscopic properties of atoms and ions that ultimately have broader applications beyond those originally envisioned. In these roles, the group provides essential measurement standards support for the national scientific, industrial, and government infrastructure. Its reputation for data accuracy and integrity, earned over many decades, makes the group a unique and irreplaceable resource on which many important constituencies around the world rely. Quantum Metrology Currently, the Quantum Metrology Group has a somewhat narrow focus compared with that of years past (driven by lack of staff, which is discussed below), with its primary areas of work in precision optical metrology, precision X-ray spectroscopy, and advanced X-ray measurements. These activities are world-class in caliber, clearly support the core function of NIST, and should be appropriately supported. Program Relevance and Effectiveness Programs in the Atomic Physics Division show a clear tracking to the NIST mission in both relevance and effectiveness. The level of support offered by the division's work to national industrial and scientific endeavors can be illustrated by several examples. The laboratory's EBIT team has estab- lished itself as a key leader in many scientific and technological challenges facing EUV lithography. It has capabilities that allow it to address important issues for astrophysics and for the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory. The group has been aggressive in establishing externally funded, high-visibility partnerships with SEMATECH, Intel, NIF, NASA, and the Harvard-Smithsonian Center for Astrophysics. The group has admirably focused its efforts to meet these exciting challenges. Of particular note here is that all aspects of the EBIT effort, the spectroscopy and collision studies of highly charged ions, and the surface modification capabilities are coherently contributing to these partnerships. The GEC reference cell work is now focusing on submillimeter absorption spectroscopy diagnostics for plasma processing. The technique provides high spectral resolution over a wide spectral range. It is used to monitor plasma temperatures, composition, and concentrations. This effort is strongly focused toward supporting industrial needs. The plasma radiation researchers have in particular established a fruitful relationship with Air Products Corporation. The VUV lithography effort has been extraordinarily productive, in terms of both advancing basic science and addressing key issues for industry. The precision studies of birefringence over the past few years have led to remarkable progress toward the very serious VUV materials problems. This work has led to well-deserved and substantial outside recognition for the NIST Physics Laboratory. Fundamental and applied AMO science efforts strongly overlap with the NIST core measurement and metrology functions. For example, theoretical work in quantum information is directly impacting advances in quantum measurements of great importance to standards.
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PHYSICS LABORATORY: DIVISION REVIEWS 18 Work in laser cooling and quantum processes is more strongly oriented toward basic research than are most other activities at NIST. However, the research directions chosen anticipate, within reason, key long-term national measurement needs. Just as earlier studies of optical "molasses" have contributed to the international time standard's being based on laser cooling technology, so the current efforts on quantum degenerate gases will likely have impacts on precision measurements, quantum computing, and clocks. The Atomic Spectroscopy Group has in the past few years successfully made the transition to computer and Web-based data compilation and dissemination tools, providing major improvements in the accessibility and ease of use of the data compilations. These changes have also enabled the more rapid updating of critically evaluated data sets, giving consumers confidence that they always have available the most current and accurate values of the data needed for their applications. For example, the fundamental physical constants previously had been updated about once every 13 years. With the release during the summer of 2003 of a fully revised version, the group will have succeeded in meeting its goal of an update every 4 years. Over the past 2 years, Internet requests for atomic spectroscopic data of all kinds have grown from an average of about 64,000 per month in calendar year 2000 to more than 94,000 per month in 2002. Internet requests for fundamental constants data averaged about 130,000 per month in 2002. Significant funded "commissions" for precise laboratory spectroscopic and other mea- surements were received from NASA, the European Space Agency, DOE, and the Electric Power Research Institute. It is clear that the Atomic Spectroscopy Group is serving the critical needs of a variety of constituencies exceedingly well. One particularly impressive theme being addressed across disciplines within the Atomic Physics Division is the support of initiatives of the microlithography industry toward significantly higher circuit densities in microelectronics. Laser lithography is rapidly evolving in the use of deep ultraviolet, and now EUV, laser light sources. The Atomic Spectroscopy Group's laboratory provided precise new wavelength standards around 193 rim for the ArF excimer laser. Previously the group obtained precise new laboratory data for lines emitted by the F2 laser near 157 nm, while another group in the division provided improved index-of-refraction data for CaF2 and BaF2, of great importance to optical designers of lithographic instruments using the 157-nm source. In a major effort to "stretch" this technology, the industry is now focused on light sources at EUV wavelengths near 13.4 nm. The spectra of highly charged ions of xenon are of major interest for this new technology. The Atomic Spectroscopy Group has now obtained new laboratory observations of these spectra at wavelengths below 14 nm. At the same time, the group is moving rapidly to compile and disseminate a comprehensive database for as manY Xe ions as possible. in support of the EUV lithography initiative. FinallY. Intel and SEMATECH , , have provided significant funding for the Plasma Radiation Group to use the EBIT to explore the properties of thin-film and multilayer structures needed in the development of EUV lithography light sources. The laboratory's expertise in x-ray optical systems is being tapped to support the U.S. fusion program by designing a diagnostic module for the NRL to be delivered to the NIF. It appears that closer ties to industry are being developed with respect to the precision optical metrology work, and additional ties should be encouraged. Connections should continue to be made with academia and industry for the biological-related X-ray activities to ensure that the proposed work is relevant to the needs of this community. If adequate staffing were available, collaborations should be sought between NIST and the third-generation X-ray synchrotron sources at which issues similar to those being addressed at NIST (high-precision angle measurement, comparison of surface roughness measurements using visible light, X-rays, and atomic force microscopy, and so on) are also being pursued. However, given the current manpower situation, it is clear that this simply cannot occur.
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182 AN ASSESSMENT OF THE NIST MEASUREMENT AND STANDARDS LABORATORIES: FY 2003 Division Resources The eroding base support for the scientific programs of the Atomic Physics Division has been offset by extensive use of contractors and visitors. However, the panel is concerned for the long-term financial health of the division. In discussions with a small sample of division contractors, it became clear that a number of issues need to be addressed. In particular, while the contractors were excited about their work and felt that they are treated very well by the NIST scientists with whom they work, they also felt that their compensation was inadequate to allow for a moderate standard of living in the area near NIST. In addition, obtaining adequate health care insurance is apparently a problem for these people. Many of the contractors are foreigners and are currently experiencing substantial difficulties with visas. Given the widespread use of contractors by NIST, it is important that the division and the laboratory aggressively pursue means to improve their situations. These issues are likely not specific to the Atomic Physics Division or the Physics Laboratory, but the panel mentions them here as an observation from staff-level discussions. The division is anticipating a long-awaited upgrade in facilities with the upcoming opening of the new Advanced Measurement Laboratory. There was concern expressed to the panel that these new facilities may be accompanied by a substantial overhead tax that would adversely affect base funding. At the time of last year's review, the Quantum Metrology Group was already at a subcritical staffing level, with just four permanent staff. Presumably because of their expertise and experience, two of those staff members were recruited to work on pressing national security problems during the past year. This situation has recently been exacerbated with the retirement of the group leader, effectively leaving 2.5 full-time equivalents (FTEs) working in the focus areas of the group, with the remaining 0.5 FTE continuing to work on homeland security. Although the remaining members of the group are early in their careers and very enthusiastic about the work they are performing, additional staff is critically needed to keep the group viable. To retain the expertise of this group a more aggressive hiring plan should be developed, embracing not only permanent staff but also postdoctoral associates and/or visit- ing scientists, or using other creative approaches to increasing staff numbers. A continuing concern over the past several years has been the long-term viability of the Atomic Spectroscopy Group, given its aging staff and inadequate funding. In last year's report the panel expressed serious concerns on this subject. It is gratifying to note that, as of this year's review, the prognosis for the group appears much improved. The Atomic Spectroscopy staff now includes several young members who can be easily viewed as forming the future core of the group. The energy and passion of these younger scientists are evident and contribute to the optimism of the group as a whole. The Physics Laboratory has provided a basic level of funding for the group, which has had a successful year in attracting new grant funding from various sources. Although the group is not growing dramati- cally, at least its situation has stabilized, and its outlook for the future is brighter. _ A matter of concern to the panel is that one or two of the promising new, younger staff members are emigrants from Russia. Their ability to join the staff for the long term depends on their ability to establish the appropriate immigration status in this country. Also, the continuing rise of overhead costs will make it financially difficult to add these individuals to the core staff unless the cost is offset by the retirement of older staff members. It is hoped that some financial flexibility will allow these transitions to be smooth and rational. Another matter of concern to the panel is that much of the division's equipment is very old. To keep up with future demands for precise atomic spectroscopic data and to attract new "business" will require steady modernization of equipment and facilities over a period of years.
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PHYSICS LABORATORY: DIVISION REVIEWS 183 OPTICAL TECHNOLOGY DIVISION Technical Merit The Optical Technology Division advances knowledge, develops expertise, provides technical lead- ership, and delivers the highest-quality standards, calibrations, and measurements in targeted areas of optical technology. Optics and optical technology are broadly construed to include the spectral range from the microwave region to the vacuum ultraviolet. The division is currently organized in four groups: Optical Thermometry and Spectral Methods, Optical Properties and Infrared Technology, Optical Sen- sor, and Laser Applications. This organization is largely administrative in nature, as productive interac- tion among individuals, groups, and other NIST laboratories is an avowed goal of division management. Within NIST, the Optical Technology Division has the institutional responsibility for maintaining two base SI units: the unit of temperature above 1234.96 K and the unit of luminous intensity, the candela. The division also maintains the national scales for other optical radiation measurements and ensures their relationship to the SI units. The division maintains a long-term, core commitment to high-accuracy measurements in radiom- etry, photometry, and spectroradiometry. It has invested significant resources in these areas and justifi- ably places emphasis on maintaining the laboratory investments and carefully derived measurement methodologies as tools for external customers in the private and government sectors. The panel com- mends the division for its continuing efforts to develop new approaches to calibration over a wide spectral range, from the far-IR through the EUV, and to seek new means of meeting customers' needs through transportable calibration techniques and technologies. New developments that enable measure- ments with greater customer convenience include the Facility for Automatic Spectroradiometric Cali- brations, FASCAL-II, a detector-based spectral irradiance calibration capability that has recently been brought online to complement the earlier version of this instrument, and the transportable Missile Defense Agency (MDA) transfer radiometer. Also addressing these needs are the SIRCUS and "travel- ing SIRCUS" systems that use tunable laser technologies. The UV-VIS SIRCUS is now fully opera- tional and is proving to be extremely useful for the calibration of various radiometers for both irradiance and radiance spectral responsivity. More than 9 decades of dynamic range have been achieved, and the spectral bandwidth is minuscule in comparison with measurements using dispersive instruments. The IR-SIRCUS is also nearing completion. These facilities support remote site work for NASA, the Na- tional Oceanic and Atmospheric Administration (NOAA), the MDA, and other DOD agencies. Also, the Thermal IR Transfer Radiometer facility will support various NOAAINPOESS (National Polar-orbiting Operational Environmental Satellite) and DOD needs over the next decade and beyond. The current development of the High Accuracy Cryogenic Radiometer (HACR-2), with higher sensitivity, greater dynamic range, and more operational flexibility than the current HACR system is another good example of the use of in-house expertise to better meet future customer requirements. A unique facility available at NIST is the SURF III synchrotron source. It offers a distinctive and important approach to absolute radiometry. New beam lines have enhanced the capabilities to character- ize detectors and components in the UV, VUV, and EUV. Transfer standards at all of these shorter wavelengths are becoming increasingly important to the semiconductor industry. The UV regime is now very critical in the semiconductor industry for lithography and metrology purposes. The panel feels that the analytical and metrology platforms created for predicting and measuring the optical properties of materials such as CaF2 and other relevant UV materials used in the semiconductor industries could now be usefully expanded.
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184 AN ASSESSMENT OF THE NIST MEASUREMENT AND STANDARDS LABORATORIES: FY 2003 Many of the classical materials have been improved or "cleaned up" dramatically relative to their state decades ago. In addition, many of the traditional optical properties need to be remeasured at shorter wavelengths and/or to greater accuracy and in some cases, at higher fluxes. It would be appropriate to undertake a study to determine which materials would merit further characterization. Much of the ensuing work would benefit from the excellent theoretical and experimental foundation built by NIST researchers. The Absolute Pyrometry project, which will ultimately result in the ability to maintain the SI scale of thermometry above a temperature of 1235 K, is progressing well. Several measurements have been made on a variety of blackbody optical radiation sources, demonstrating the feasibility of this approach. Plans have been made to extend to lower temperatures using InGaAs and InSb detectors to connect with ideal gas thermometry. Similar plans have also been made to realize an accurate scale at elevated temperature using high-band-gap detectors. This work supports the national responsibility for maintain- ing the SI scale of temperature. Optical materials characterization is an important and vital part of the division's activities. A long tradition of expertise and instrumental capabilities is available for infrared studies. At present, the FTIR facility for materials characteristics and standardization continues to show good progress. Only a few steps remain before this instrument becomes fully operational. This is a unique facility that permits simultaneous infrared measurements of emittance and reflectance with multiple blackbody sources for wide wavelength coverage. It will be a valuable complement to the division's extensive infrared charac- terization capabilities. The use of light-emitting diodes (LEDs) for lighting, signaling, and display applications is a growth industry, prompted by the continued advances in LED spectral coverage, versatility, and efficiency. The Optical Technology Division has recognized the expanding needs for LED characterization and associ- ated photometric standards and has evolved its tools and adapted its resources to meet these needs. The capabilities now exist to measure intensity, flux, angular distribution, and spectral properties of LED devices as a function of their operating conditions (drive current and temperature). Packaged tempera- ture-controlled LED s are being characterized and may make useful standards. New calorimetric facili- ties are employed for their spectral characterization, and they may also be applicable for calorimetry of new LCD display devices. The NIST calibration services for color-measuring instruments used by the private sector lighting and display industry will be well used in future years. Another recent initiative concerns the instrumentation to characterize retroreflective materials and the development of corresponding standards. The radiometry/source end is nearly complete, and the sample goniometer is in the design phase. The panel believes that this is an important project that has diverse types of potential impact, notably in the area of highway safety. The Optical Technology Division is active in providing unique new spectroscopic tools and applica- tions in selected areas. Currently, one of these focus areas is the exploration of the terahertz or far- infrared spectral region. This part of the electromagnetic spectrum is of great scientific and technologi- cal importance but has traditionally been a difficult one to access because of the lack of tunable coherent sources. In a laboratory-wide Competence program, new sources, techniques, and spectroscopic appli- cations are being developed. The division continues to be a leader in these areas. Both continuous-wave and time-domain spectroscopic techniques are being developed and refined. The CW techniques are based on specialized electron devices, as well as on the extension of traditional approaches using FTIR methods. The time-domain methods utilize the division's extensive expertise in femtosecond lasers and nonlinear optics to generate and detect single-cycle pulses of far-infrared, terahertz (THz) radiation. These new capabilities are being used for measurements that include studies of biological molecules and
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PHYSICS LABORATORY: DIVISION REVIEWS 185 their building blocks research that is resulting in numerous publications. Applications to biotechnol- ogy and national security are clear. For example, although the absorption spectra of proteins and their building blocks are exceedingly complex, the identification of resonance structures that can be distin- guished from those of sugars and cellulose provides the potential for spectral discrimination techniques. The laboratory resources for this work are well organized and well maintained. Taken in totality, the division' s terahertz radiation program is one of the most extensive and advanced in the world. Small structures represent another major frontier in optical spectroscopy, with significant impact in priority areas from semiconductor technology to biotechnology, as well as great inherent scientific interest. In response to needs in this area, unique capabilities have been and are currently being devel- oped to probe thin films, surface layers, organic and inorganic nanostructures, and even single mol- ecules. These activities are well aligned with other major initiatives in NIST and with areas of external importance, such as bio- and nanotechnology, photonics, and electronics. With respect to precision measurements of surfaces and interfaces, the broadband, infrared-visible sum-frequency generation spectroscopy pioneered in the Optical Technology Division provides the power of an interface-specific optical technique with the possibility for rapid data collection of vibrational spectra. The division team has demonstrated the utility and uniqueness of this approach in several noteworthy studies. These contributions have had a marked impact on laboratories throughout the world. In ongoing investigation, recent advances have included the use of doubly resonant (vibrational and electronic) excitation to enhance the sensitivity and selectivity of the method. This has been successfully demonstrated in studies of the chemical groups in DNA monolayers. In complementary work, the division has successfully initiated the development of new, optical scattering metrology techniques and associated models that have a broad range of applications in studies of surface structures, film or layer properties, and particle deposition on surfaces. This research is an outgrowth of the division's established expertise in the precise analysis of optical scattering. Recent developments have direct relevance to the semiconductor industry. The associated development of a public-access library of software tools for customers to use in their own particular applications areas has been very successful. It is difficult to quantify the impact that this type of service has on the larger community, but the fact that the software library Web site has experienced more than 1,000 downloads in the past year is a good indicator. The laboratory facilities for this initiative are currently constrained and could certainly benefit from the commitment of more space, particularly in a low-vibration environ- ment. Plans for expansion should be realized in 18 to 24 months when a new building becomes available for occupancy. There may be significant added benefit of this work to the semiconductor industry bv extending the instrumentation into the UV. The ultimate limit of spectroscopy for small structures addresses the detection of single molecules. To meet this challenge, the division has a leading-edge program to develop the necessary tools and techniques for such measurements and to pursue significant applications to problems of biological significance. These measurements rely on the division's expertise in confocal and near-field microscopy and fluorescence detection of weak signals. This knowledge has permitted researchers in the division to perform impressive experiments on the measurement of distances on the nanometer scale by means of an adaptation of the technique of fluorescence resonant energy transfer. These investigations have the potential for significant impact in biophysics and biotechnology. A key ingredient in the success of this program is the very strong integration of these and other efforts in the division with unique resources available from the nearby NIH facilities. The panel was struck by the very close collaborations that had been established and by the mutual benefits to both sides resulting from these interactions.
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196 AN ASSESSMENT OF THE NIST MEASUREMENT AND STANDARDS LABORATORIES: FY 2003 As was mentioned earlier, with the exception of about 6 weeks during calendar year 2002, the burden of day-to-day management of the Radioactivity Group was the responsibility of the division chief. Although this situation was not ideal' it was manageable for 18 months while the croup leader was O O 0 1 on a rotational assignment to the lndustr~al Liaison (ice within the NlS l directors s office. Next year similar managerial changes are on the horizon, with the division chief on leave for a year to the new Department of Homeland Security and the Radioactivity Group Leader serving as the acting division chief in his absence. This arrangement raises questions about continuity in leadership within the divi- sion. These changes and others that might result must be made carefully so as to preserve the strong management team and to keep the momentum and morale high among the staff. All of the groups within the division feel the need to bring on additional staff. After a considerable downsizing of the division in the early to mid-l99os, the total number of division personnel has stabilized, remaining essentially constant over the past 5 years. However, during this same 5-year period, the responsibilities of division personnel and thus their workloads have changed in two impor- tant ways. First, the requirements for their core mission involving standards and calibration services have increased substantially. (Examples include the use of the neutron imaging facility for imaging chemical processes in fuel cells and the standards and calibration work associated with brachytherapy seeds, as well as standards and protocols for newly approved radiopharmaccutical agents.) Second, since September 11, 2001, the division has acquired new responsibilities, some funded and some unfunded, in support of homeland security. The increased workload, coupled with flat or declining budgets over the years, has put a strain on the existing workforce to the point that many staff members feel that there is little or no time for fundamental research or program development in traditional areas. In some cases, the research that is being done is carried out by necessity, and is focused on more applied metrology problems in support of the standards and calibration work. This research, although very applied, is in direct support of the expressed needs of the communities that the division serves, and its importance should be both recognized and supported by the Physics Laboratory and higher manage- ment. In the Radiation Interactions and Dosimetry Group, at least two new hires are needed. First, a staff member is needed in the area of theory and modeling a key hire in the effort to attain a critical mass with respect to supporting needed cross-section calculations and addressing new code development and other theoretical areas. Previously the staffing in this area had dropped to a single individual, who had both managerial responsibilities and full responsibility for the theoretical effort. Most recently a new staff scientist was added, but because this group remains the only such group in the nation committed to this area, an additional hire is warranted. The second key hire is for a person to champion the develop- ment of new standards, applications, and uses for the Clinac and SureBeam accelerators (see the preceding discussions of the equipment). Other needed hires for this group are two Ph.D.-level radio- chemists, one to support the growing business associated with radiopharmaccuticals (particularly since the lead investigator is leaving for another multiyear position), and the other to take over the group's SRM program when the current leader of the program retires later this year. The Neutron Interactions and Dosimetry Group has its own dedicated experimental beam lines and generally is well equipped to carry out its goals and responsibilities. It has a good balance of experienced senior researchers, but this group, along with others in the division, has remained constant in numbers of personnel while assuming new responsibilities such as those for homeland security. This group and others would benefit from a mechanism for providing a reliable and continuous source of postdoctoral fellows and junior research staff. In turn, such appointments would be a national resource of new scientists.
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PHYSICS LABORATORY: DIVISION REVIEWS ties: 197 TIME AND FREQUENCY DIVISION Technical Merit The Time and Frequency Division supports U.S. industry and science through the following activi- · Development and operation of standards of time and frequency and their coordination with other world standards; · Development of optical frequency standards supporting wavelength and length metrology: · Provision of time and frequency services to the United States; and · Basic and applied research in support of future standards, dissemination services, and measure- ment methods. ~ ~.', The work supporting length metrology derives from the dependence of the meter on the realization of the second. This work contributes to a larger program in the Manufacturing Engineering Laboratory's Precision Engineering Division, which has primary responsibility for length and its dissemination. The division is organized in six technical groups, which are small in size but show very strong integration. These groups are Atomic Standards, Ion Storage, Time and Frequency Metrology, Network Synchroni- zation, Optical Frequency Measurements, and Time and Frequency Services. The overall impression of the panel is that the Time and Frequency Division remains technically strong, with a healthy balance of applied and basic programs. This division serves a unique and valuable purpose for scientific and technical communities in that it is the caretaker of the nation's primary standards for time and frequency measurements and possesses the knowledge and expertise to advance the precision and accuracy of these measurement capabilities. Details of current programs and their merit are discussed, by group, in the following subsections. Atomic Standards The Atomic Standards Group has made considerable progress in several areas that address the continuous refinement of time and frequency measurements based on atomic standards. The cesium fountain standard, NIST-F1, is established as the nation's primary standard. The frequency uncertainty of NIST's F1 is 1.2 x 1o-~5. The division is focused now on improvement in the reliability and automa- tion of NIST-F1, to provide more regular data. On the basis of the efforts of this group, NIST continues to define the state of the art in these measurements and is "tied for first place" with the Physikalisch- Technische Bundesanstalt in Germany for the performance of its primary frequency standards. Last year's clock comparison with PTB was the best ever, at 5 x 10-~6. Design work continues on the second-generation NIST fountain, NIST-F2, which will load the atoms from a low-velocity intense atom source. NIST-F2 will use only one laser and will operate with a liquid-nitrogen-cooled drift space to control the uncertainty in the blackbody radiation frequency shift below 1 x 10-~6. The vision for NIST-F2 is to control the spin exchange frequency shift well enough to reduce its uncertainty to less than 1 x 10-~6 by tossing multiple balls of atoms into the interrogation region. This uncertainty is needed to measure the gravitational shift in the Primary Atomic Reference Clock in Space (PARCS) experiment. Operations at liquid nitrogen temperature will also help control the frequency shifts induced by background gases. The overall accuracy goal for NIST-F2 will be 5 x lo-16.
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198 AN ASSESSMENT OF THE NIST MEASUREMENT AND STANDARDS LABORATORIES: FY 2003 To support solid comparisons of primary frequency standards at the sub-10-l5 level, improvements are being made in the stability of the NIST coordinated universal time (UTC) at the sub-10-5-level timescale with respect to the UTC disseminated by the Comite International des Poids et Mesures. A complete replacement of the timescale hardware was due in January 2003; the existing equipment is more than 20 years old and has severe reliability issues. New electronics have already improved the signal-to-noise ratio substantially. Finally, new software is being written to appropriately weight the clocks in the ensemble and produce the output. The continued improvement of time transfer is a key support element for primary clock comparison between international laboratories. Recently the U.S. Naval Observatory and NIST have undertaken a series of experiments to improve the performance of two-way time transfer. One comparison per hour has provided much-improved understanding of systematic and environmental effects. Tentative plans involve having a two-way satellite relay station installed at the Kauai, Hawaii, radio station site to better cover trans-Pacific Ocean two-way time transfer. The two-way satellite time transfer equipment will have upgraded hardware this year; receiver up- converters with temperature sensitivity of <5 ps/°C will greatly reduce environmental effects. New GPS receivers are also being acquired. Two-way time transfer and the GPS carrier phase are comparable in performance, approaching 100-ps precision, which is the state of the art. The two techniques are both needed to provide a means of comparison: they mutually support one another's evolutionary improve- ment. The capability to do 200- to 300-ps time transfer with PTB last year enabled frequency compari- sons at the 5 x 10-~6 level with a 20-day averaging time. The current goal for two-way time transfer is 100 ps, which will likely need ionospheric corrections. Ion Storage The Ion Storage Group is devoted to the development of clocks based on mercury ions as well as to an effort in quantum logic. Two years' worth of data comparing the frequency of cesium to the mercury- ion is now available to project the constancy of these two measurements. With no control of systematics, the change in frequency of the mercury ion with respect to cesium is observed to be less than le- 14. This surprisingly good performance suggests that even better results should be possible. A key achievement of the past year is the definition of a universal logic gate, the so-called geometric phase gate. This gate appears to substantially ease requirements on lasers, for example, and is thus well suited to scaling the systems to larger numbers of ions, which in turn offers the potential for realizable, large-scale quantum computers. Time and Frequency Metrology Efforts of the Time and Frequency Metrology Group continue to develop phase- and amplitude- noise measurement capability and techniques for frequencies up to 100 GHz. This regime is far beyond the range of commercial instrumentation, and it has applications in high-speed digital devices, broad- band telecommunications, and radar. The group's past work on the development of techniques for the measurement of phase noise of pulsed radar tubes is now in place in industry and working very well. The division's capabilities in this area are unique, both within the United States and internationally. The group recently developed a clever means of adding a synthesizer to a reference oscillator in such a way that a single cavity can be used to clean up the noise. As a result, NIST will be able to handle measurements with larger dynamic range much more efficiently. Another highlight is the demonstration of a new measure of variance, which allows extension of averaging time to the length of the measure-
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PHYSICS LABORATORY: DIVISION REVIEWS 199 ment interval. In contrast, the standard Allan variance provides data for only a fraction of the measure- ment interval. This new variance has obvious practical implications for characterizing long-term fre- quency stability in a shorter measurement interval, having a positive impact on the cost of frequency stability testing. The group works on broadly tunable oscillators and participates in three Defense Advanced Re- search Projects Agency (DARPA) programs, which brings in approximately $1 million of external funding. With DARPA's new interest in narrowband microwave systems, funding is likely to increase further next year, so this group is likely to expand. Network Synchronization Currently the Network Synchronization Group is supporting standards projects primarily in the areas of time coordination and timescale upgrades. A collaboration between this group and the Univer- sity of Colorado is aimed at improving the GPS carrier-phase method. Developments in this area will also be used for the PARCS space-clock mission. A highlight of recent work on the timescale is the development of improved steering of the timescale to UTC. This has reduced deviations of UTC(NIST) from UTC by a factor of two. Optical Frequency Measurements The Optical Frequency Measurements Group continues to develop and extend the applications of the optical frequency combs. These have been produced by injecting femtosecond pulses from a mode- locked laser into a microstructure fiber to broaden the spectrum to the required octave. A new mode- locked laser now directly produces an octave-spanning spectrum, which eliminates the need for the nonlinear fiber. This change increases the reliability of the system, which can now stay phase-locked for a day rather than a few hours. An optical frequency standard with a microwave output is obtained by locking a mode of the laser cavity to an atomic transition. This approach has the potential to achieve uncertainties 1,000 times better than those of the current best standards. To date, the electrical micro- wave signal generated by detecting the optical pulse train is somewhat noisier than the pulse train itself, but progress is being made on this issue. Substantial progress can be reported on the extension of frequency-comb technology to 1.3- and 1.55-pm wavelengths in support of wavelength-division-multiplexing (WDM) systems to be constructed at these telecommunication wavelengths. A chromium-doped forsterite laser has been mode-locked and emits a 400-MHz pulse train at ~1.3 ~m. These pulses will be frequency-doubled to obtain 657-nm light that will be locked to the corresponding transition of the Ca atom. Frequency combs could act as the basis for precision length measurement (at the 1 x 10-8 level), distributed by GPS. The calcium optical frequency standard, based on a narrow resonance in calcium atoms that are laser-cooled and trapped in a magneto-optical trap, has very good short-term stability, limited primarily by the atomic velocity. Because its Q (the ratio of transition frequency to linewidth) is lower by two orders of magnitude, it does not appear to be in serious competition with the mercury ion standard for use as a primary standard, but it is useful for comparisons of optical standards. In the past year, quenched cooling of the calcium atoms has been implemented, and this reduces the linewidth from millikelvin to microkelvin levels. The short-term stability is 3 x 1o-~5 at Us averaging time. A new approach under consideration is to establish a lattice structure of 106 calcium atoms to reduce the Doppler effects even more. There are no major theoretical obstacles to this approach.
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200 AN ASSESSMENT OF THE NIST MEASUREMENT AND STANDARDS LABORATORIES: FY 2003 Substantial work is already under way in the development of a low-power chip-scale atomic clock with a total volume of 1 cm3. Scaling laws for small (millimeter dimensions and smaller) buffer-gas cells are being studied using an apparatus that allows continuously variable spacing between two glass surfaces. Small gas cells have been successfully fabricated using glass capillary tubing, but efforts to make cells using silicon bonding to glass are not yet working. Success with the capillaries is sufficient to reach the first-year milestone for the project. Time and Frequency Services The Time and Frequency Services Group provides access to the division timescale via telephone and network time messages and radio transmissions from WWV, WWVB, and WWVH. The Internet Network Time Protocol servers at NIST now handle traffic of 1 billion hits a day, and the number continues to grow. The upgrade in transmitted power from WWVB has enabled a broad and growing range of low-cost mobile and consumer time products, which now function across the continental United States. Japan now has a station at the same frequency, which means that nearly common products can serve two markets. This capability will provide a natural stimulus for further commercial develop- ment. Program Relevance and Effectiveness The Time and Frequency Division at NIST represents an important and highly valuable capability of national significance. The services provided by the division are crucial to the users in commerce, industry, the scientific community, and universities. The supporting research and development is first- rate and relevant to the charge of the division. As an example, this group maintains the division Web site, which is becoming the broadest and most valuable means of disseminating time and frequency measurement knowledge. Many of the technical papers produced by the division are available on the Web; soon all division publications will be available through this channel. A major benefit of the Web site is that it provides efficient and consistent answers to customers, who provide positive feedback regarding the site. The site also pro- vides a venue for keeping the division informed of new directions in customer needs. Finally, workshops and seminars presented by the division provide valuable service to the commu- nity. As an example, the NIST Time and Frequency Tutorial drew more than 50 people in 2002, including representation from many new sources such as DARPA and the Lincoln Laboratory. Survey data from this tutorial indicate high customer satisfaction. Division Resources Time and Frequency Division resources are growing at a reasonable rate, and the division continues to attract and retain high-quality personnel. It is staffed at a level sufficient to continue good progress on scientific and technical projects, and overall is reasonably well supported. The retirement of a veteran investigator in 2003 will create a serious void in capabilities. As a transitional measure, this employee has agreed to remain as principal investigator for the PARC S project. The self-admitted weakness of the division is in continuous operation of the primary standards. The NIST-F1 fountain was built in a hurry because NIST was behind in the international primary frequency standard community. NIST is now returning to upgrade the systems of NIST-F1 to improve its opera-
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PHYSICS LABORATORY: DIVISION REVIEWS 20 tional reliability. One member of the staff is focused on automation of NIST-F1. Burnout of staff is a concern, and the hope is that automation will reduce the potential for this problem and allow staff to focus on the design of the new fountain, NIST-F2. As a whole, the development of the primary standard could benefit from additional attention to applying good engineering practices when building or upgrad- ing the clock. The maser ensemble continues to serve as the operational flywheel for NIST-F1 evaluations. Noise in the timescale currently limits comparison of the Cs standard to the timescale. New hardware will replace masers that are more than 10 years old. New electronics have already improved the signal-to- noise ratio substantially. Finally, new software is being written to appropriately weight the clocks in the ensemble and produce the output. Division laboratory space has been improved markedly. Two new laboratories with exceptional environmental controls have been constructed. These laboratories will house the laser and quantum logic work and have the best environmental controls on the site. Old space will be renovated and used for the fountains. New laboratory space for optical frequency measurements and the chip-scale clock project will be completed soon. There is a plan to renovate all division laboratories over the next 10 years. At this time, however, the cesium primary standard is housed in a laboratory with a leaky roof. The test and measurements laboratory is hindered by the interference of RF and microwave signals in the building, and is likely to be limited in its capability to conduct noise measurements with the needed sensitivities. QUANTUM PHYSICS DIVISION Technical Merit The Quantum Physics Division makes up the NIST portion of JILA (formerly the Joint Institute for Laboratory Astrophysics), a joint institute with the University of Colorado. JILA is a multidisciplinary research organization whose principal researchers are the JILA fellows, about half of whom are univer- sity faculty members and half NIST employees. The mission of the division is to provide fundamental understandings of nano-, big-, and quantum optical systems through investigations of new ways to direct and control atoms and molecules, measurements of chemical and biological processes and their interac- tions with nanostructures, and exploitation of interactions of ultrashort light pulses with matter. The partnership with the University of Colorado embraces a technical strategy to help produce a new generation of scientists. The overall aim is to produce world-class fundamental research with the potential to improve measurement science. This assessment covers only the Quantum Physics Division; the panel did not review all of JILA this year. Major thrusts of the laboratory and its achievements are discussed below. Quantum Atom Condensates The Quantum Physics Division has a history of recognized technical excellence in its areas of emphasis, which it continues to maintain and expand. It has been a leader in the field of neutral atom cooling and trapping and in the first observations of Bose-Einstein condensates (BECs) of neutral atoms, leading to the 2001 Nobel Prize in physics for two JILA fellows. Quantum dynamics of BECs continues to be a major area of strength for the division, with two NIST fellows maintaining innovative research programs.
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202 AN ASSESSMENT OF THE NIST MEASUREMENT AND STANDARDS LABORATORIES: FY 2003 The behavior of BECs is being explored in order to understand the nature of fundamental elemen- tary excitations of these macroscopic quantum systems. In particular, angular momentum of a spinning condensate is trapped in a lattice of vortices; these vortices display interesting dynamics of their own, including phase transitions from translationally invariant "solid" phases to liquid phases in which the vortices undergo more complex dynamics and "striped" phases involving strong shear flows of atoms. Another possible state when the atom cloud evolves into a pancake-like quasi-two-dimensional state is analogous to the two-dimensional electron gas in solids that displays the famous quantum Hall effects. This analogy between dynamics of the BEC of atoms and related condensed matter systems is a major thrust of research that may shed new light on the behavior of both classes of systems and phenomena. Other ongoing research includes precision spectroscopy of ultracold atoms and the injection of a BEC into a lithographically patterned microstructure a "BEC on a chip" with the long-term goal of devel- oping ultrasensitive inertial sensors using atom interferometry. Another important area of ultracold atom research involves the study of degenerate Fermi gases of ultracold atoms, in which the quantum mechanics of fermions show interesting new phenomena, includ- ing the first observation of a Feshbach scattering resonance in fermionic atoms and potentially the formation of atomic Cooper pairs in an atomic superfluid phase. A new quantum condensate consisting of both cold Bose and Fermi atoms has also been produced and is being characterized. Laser Stabilization and Control The Quantum Physics Division has been a consistent pioneer of laser stabilization science and technology that has found its way into other NIST laboratories, into basic optical physics projects around the world, and into commercial laser products. Recent work has seen a significant extension of achievements in the area of laser stabilization with the development of laser frequency standards based on mode-locked lasers. This work, a collaboration of three NIST fellows, promises to revolutionize the field of optical frequency measurement by the introduction of methods to control to very high precision both the repetition rate and optical frequency, and ultimately the phase of trains of mode-locked laser pulses. The importance of this technology is that it extends the wavelength coverage of available precision optical frequencies tremendously and enables new techniques for the coherent control of optical fields. For example, it has enabled two mode-locked laser oscillators to be precisely synchro- nized for the first time, with a timing jitter in the femtosecond regime. This new level of control has already led to applications such as coherent anti-Stokes Raman spectroscopy (CARS) imaging (see below) at unheard-of sensitivity and signal-to-noise ratios. Through the use of stabilized femtosecond frequency combs, it has been possible to transfer optical frequency standards from the JILA campus to the NIST Time and Frequency Division and vice versa using optical fiber links. Independent comparison can thus be carried out in the two laboratories, 7 km apart, of independently derived standards with a precision of 3 x 1o-~5 in a 1-s measurement. Precision Spectroscopy of Cold Atoms and Molecules The spectroscopy of atomic systems that may provide new frequency standards in novel ways is being explored using the stabilized frequency comb technology. Laser cooling of 87Sr atoms appears to be the best path to a neutral atom frequency standard. In another project, OH molecules are being cooled via supersonic expansion and then slowed electrostatically for trapping in an electrostatic trap, provid- ing the first opportunity for experiments on an ensemble of chemically interesting cold molecules.
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PHYSICS LABORATORY: DIVISION REVIEWS Quantum Dots 203 Developments in apertureless near-field-optical-microscopy techniques have been exploited using quantum dots, showing the power of the method to enhance the fluorescence of very small objects of 3- to 6-nary dimensions. The new developments greatly extend the earlier ones made using molecules embedded in polystyrene spheres. A tapping mode atomic force microscopy method has been demon- strated to enable placing the probe nearer the sample, enhancing resolution and sensitivity. Ultrafast Carrier and Spin Dynamics in Semiconductors Many proposals to implement quantum information processing in solid-state systems suggest that coherent spins or excitors in semiconductors could be used to transmit and process quantum bits. Exciton coherence in GaAs is strongly influenced by many-body and phonon scattering effects and is complex to measure and to model theoretically. Likewise, spin coherence is lost through a variety of mechanisms operative in a range of doping and excitation conditions. Experiments in the Quantum Physics Division seek to provide fundamental measurements of these processes that would facilitate advances toward useful quantum information processing concepts and toward the realization of "spin- tronic" devices, which use the spin of the carriers rather than the charge for the transport of information. Femtosecond Comb A major development is under way to exploit the frequency techniques developed in JILA in order to effect quantum control in a unique way. In contrast to the electronics arena, in the optical field, phase control of pulses has been difficult to achieve and employ. Through outside support, the comb methods are being used to enable the relative phases of ultrashort pulses (e.g., 6 fs) to be controlled, ultimately allowing the synthesis of arbitrary pulsed optical fields. These methods will be useful in new approaches to quantum control and nonlinear optical processes. Biological Physics Biological physics is a relatively new area for the Quantum Physics Division. It is an inherently cross-disciplinary field, offering a significant opportunity for JILA to interact strongly with other members of the University of Colorado community. There are basically four projects that have a biological emphasis at JILA: 1. Single Molecule Imaging and Sub-nanometer Resolution. Measurement of the position of pro- teins bound to DNA in a time-dependent manner is being pursued in a newly constructed laboratory facility at JILA, and a number of collaborations have been developed with biologists on the University of Colorado campus who have interesting systems to study. The way should now be clear for exciting studies on the single-molecule dynamics of highly sophisticated proteins that process DNA molecules, allowing studies of the detailed manner in which single molecules interact with DNA and perform some of the fundamental steps of gene expression and control. 2. CARS on Single Cells. CARS is a potentially zero-background, spectrally sensitive imaging technique that can produce images of the distributions of molecules on a microscopic surface or volume. The molecules are selected by resonant scattering of unique vibrational transitions. JILA investigators have demonstrated the imaging of lipid molecules on cell surfaces, a very important subject in under-
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204 AN ASSESSMENT OF THE NIST MEASUREMENT AND STANDARDS LABORATORIES: FY 2003 standing signal transduction in cells. This technique is enabled by the availability of synchronized, frequency-stabilized femtosecond lasers developed at JILA, which allows near shot-noise-limited detec- tion sensitivity. This project is a collaboration with Harvard University. 3. Biomolecular Fluorescence Microscopy and Conformational Dynamics. The use of a high-nu- merical-aperture confocal microscope is enabling the conformational dynamics of single biomolecules to be probed employing polarization resolved fluorescence detection. The dynamics of the molecules are extracted via time-correlated single-photon counting. Particularly valuable and detailed information is being gained on the fluorescence-resonant-energy transfer between donor and acceptor dyes on a single DNA strand, and by time-resolved polarization effects. 4. Dynamics of Single DNA Molecules in Gels. The dynamics of DNA molecules is being studied using high-speed, single-molecule imaging. Gel electrophoresis is a cornerstone technology of molecu- lar biology, and key aspects of how electrophoresis of long DNA molecules occurs are still not under- stand in detail. Program Relevance and Effectiveness The Quantum Physics Division, along with its JILA partners, provides innovative fundamental advances at the frontier of science that are of interest because they have high potential for future advances in measurement science and technology. The division also continues to refine technology of proven utility to NIST measurement science programs, such as advanced laser stabilization methods. Further, the division provides a pool of talent that can respond to special needs in response to homeland security. For instance, one NIST fellow is actively pursuing methods for the sensitive laser-based detection of anthrax spores. By virtue of its association with the University of Colorado, the division has access to a talented pool of graduate students and postdoctoral researchers, and among the most valuable products of the division are the talented and capable scientists that it graduates into positions with other divisions of NIST, in industry, and on university faculties. At least 47 JILA graduates have moved on to employment within NIST. The division has been effective in strengthening its existing core areas of emphasis, with continued pursuit of the frontiers of understanding through experimental programs, including those in the areas of cold atoms, precision spectroscopy and frequency standards, quantum phenomena such as BEC, and advanced laser control and stabilization. New areas of potential importance have been identified (e.g., biophysics, quantum information), and strategies have been developed for making significant initial contributions toward ultimate leadership. The panel perceives a general overall evolution of the strengths of the division in response to changing needs for measurement science and the fundamental research needed to support future measurement science. The Quantum Physics Division is active in collaborations with university groups, industry, and other NIST sites. Examples include the development of CARS imaging of living cells with a Harvard group, the advancement of short-pulse generation by means of laser stabilization and control with an MIT group, and the comparison of optical frequency standards with the Time and Frequency Division, made possible by a fiber link to that division. The Quantum Physics Division is fundamentally a basic research and student education facility, and it performs these functions very well, as shown by its excellent record of scientific publications and presentations and by awards recognizing its accomplishments. In addition to the past Nobel Prize in physics, division researchers have recently been awarded the Max Born Award of the Optical Society, the Presidential Rank Award from the U.S. Office of Personnel Management, the William O. Baker
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PHYSICS LABORATORY: DIVISION REVIEWS 205 Award of the National Academy of Sciences, the Maria Gooppert-Mayer Award of the American Physical Society, and the Presidential Early Career Award for Scientists and Engineers, and one was named among the "100 Top Young Innovators" by Technology Review. The development of the stabilization and synchronization of femtosecond pulses from two lasers has had an immediate impact with the commercial femtosecond laser producers, which have enthusias- tically adopted the technology. The importance of mode-locked laser stabilization to the many applica- tions of these lasers in chemistry, physics, and biological science and to the manufacturers of these laser systems has emphasized the need for a clear intellectual property policy that is known and understood by the NIST scientists. The lack of such a policy has been a significant impediment to the dissemination of this technology to the laser community, and it has resulted in significant misunderstanding among JILA scientists as to the ownership of intellectual property. The division has taken the initiative in opening a dialogue with NIST intellectual property lawyers to clarify these issues, but much work remains to be done in order to define a set of principles that can guide NIST scientists in these matters on a routine basis. This panel cannot emphasize too greatly the need for clear intellectual property policies and procedures to facilitate elective interactions with industrial partners. Intellectual property information should be summarized in a simple set of guidelines that staff members can understand and follow. The staff should also have direct access to Intellectual Property Department personnel for the resolution of specific issues that arise during the patenting process. Biological Physics has three basic sectors: fundamental research, applied biotechnology, and bio- medicine. The four projects now under way at JILA are in the fundamental research sector, although there are certainly avenues that will lead to applications in biotechnology and biomedicine. However, the training of a new generation of biological physicists is very important as biology becomes ever more sophisticated; JILA will act as an important source of young scientists with strong "hard science" backgrounds, moving into biology using the tools of physics and related fields. The effort in biological physics clearly identifies a new area of potential importance and a strategy for making significant initial contributions toward ultimate leadership. There are few physicists at present who have significant training in biological problems, and they will be essential for future growth in this discipline as biology continues to grow in sophistication. Collaboration among JILA projects is an important component of the division' s environment. Such collaborations exist in the areas of cold atoms and quantum condensates, application of stabilized femtosecond lasers, and biophysics. In biophysics, there are strong efforts to collaborate with the very strong programs in biology at the University of Colorado, and the potential is great for the biologists to begin to address important questions about how biomolecules function at the level of life processes. Closer collaborations within JILA of the three people involved in biological physics would be benefi- cial. Division Resources The Quantum Physics Division continues to nourish and build a highly qualified staff for the performance and extension of its capabilities. A new NIST fellow was hired this year with expertise in the physics of electrical circuits, quantum coherence effects, and quantum computing with supercon- ducting tunnel junctions. This new endeavor brings another potentially important perspective to the division. Building on recent past accomplishments, it has been demonstrated that at low temperature, electrical circuits can be modeled in terms of quantum coherence for high-impedance objects. The ability to make transitions between states with varying numbers of Cooper pairs has been shown. Promising activities that are being pursued offer the prospect of producing entangled states of electrical
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206 AN ASSESSMENT OF THE NIST MEASUREMENT AND STANDARDS LABORATORIES: FY 2003 circuits, the ability to do single-electron counting, the development of faster electron-counting methods, and achieving new developments in nanoscale circuits such as circuits that could be assembled using carbon nanotubes. In last year's assessment, the panel raised important and disconcerting issues about the relationships between the Chemistry Department at the University of Colorado and JILA, brought to the fore by the loss of a valued senior NIST-JILA fellow. The panel was very pleased to find that both organizations have made a concerted effort to address this issue and that past problems have been very amicably resolved, to the benefit of both parties. The current level of job satisfaction among NIST fellows seems very good. The 10 NIST fellows interviewed in this assessment uniformly praised JILA as a wonderful environment in which to do science, to the extent that those most sought after have rejected excellent offers from other prestigious institutions because they feel that JILA offers the optimum atmosphere, infrastructure, and opportunities for interactions with colleagues and for collaborations that allow them to be more creative and efficient in following up on their ideas than would be possible elsewhere. Recruitment efforts have been very active in identifying strong candidates in biophysics and cold atom condensates that would add breadth and creativity to the JILA programs in both these areas. It is apparent to the panel that the division has been proactive in strengthening its core activities. Recruitment of top-flight researchers will remain a priority as several senior NIST JILA fellows reach retirement age . . In comma years. The lack of sufficient laboratory space continues to be a concern for JILA. When the existing building was originally constructed, provision was made to create additional space by adding stories. Partial funding for this project from NIST and the university seems to be in place. The panel strongly recommends that this expansion be aggressively pursued. Biological physics as practiced at JILA provides a rather challenging combination of facility sup- port issues. JILA is well prepared to address some aspects of this challenge: that is, vibrationally quiet spaces for high-resolution imaging, very well managed clean air flow, and room temperature control. More difficult challenges will be the development of an appropriate wet-lab space, to include placement of chemical fume hoods, incubator space for cell cultures, adequate provisions for glassware cleaning and storage, and wet chemical benches. Ultimately, issues of homeland security involving biowarfare may require the construction of secure biological rooms with controlled access and guaranteed negative air pressure. It might well prove useful for future growth in such a broad field to consider putting biological physics facilities in a well-defined floor of JILA to facilitate interactions, to share common facilities, and to restrict access to potential biohazard areas.
Representative terms from entire chapter: