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Technical Highlights

Precision Measurement of Lasing Lines for Deep UV Photolithography. In the near future, the production of integrated circuits for computer chips is expected to utilize microlithography based on a fluorine (F2) excimer laser operating at 157 nm. Because the index of refraction of materials to be used for projection optics varies rapidly with wavelength, the wavelength of the laser must be known to high accuracy. In a collaboration with a leading manufacturer of these lasers, the Lambda Physik Corp. of Ft. Lauderdale, FL, we utilized the unique capabilities of the NIST spectroscopy facilities and applied our 10 m vacuum spectrograph together with a well-characterized Pt/Ne hollow-cathode lamp to measure the wavelengths of six lasing lines from one of their developmental F2 lasers to an accuracy of 1 part in 107. For this experiment a novel beam line was designed that eliminated shifts in wavelength that might have been caused by slightly different illumination of the optics by the laser and the Pt/Ne lamp. We also investigated the variation of the wavelengths and intensities of the lasing lines with the operating conditions of the laser. A tracing of a portion of the recorded spectrum is shown in Fig. 1. Our measured wavelengths for three of the F2 lines are given here. The line at 157.402 33 nm was one of three newly observed lasing lines. (C. Sansonetti and J. Reader)

Figure 1. Tracing of lasing spectral lines of an F2 laser together with lines of a reference Pt/Ne hollow cathode lamp.       Measured wavelengths for three of the prominent lines are 157.402 33 nm, 157.524 33 nm, and 157.630 94 nm.

• Spectroscopic Measurements for Lighting Applications. About 20 % of all electricity generated in the United States is used for lighting, and improvement of the energy efficiency of lighting systems is a national priority. We are assisting the Electric Power Research Institute (EPRI) in its program to develop more efficient light sources with better color rendering. Our studies of rare earth elements that are used as additives in high-intensity discharge lamps have been centered on holmium. Comprehensive data on energy levels and transition probabilities for the neutral and singly-ionized spectra of this element were needed to realistically model the performance of new lamp designs. The spectrum of holmium is very dense and characterized by broad hyperfine structure patterns with as many as 24 components which frequently overlap. But our high-resolution Fourier transform spectrometer is one of the few instruments capable of handling such complex cases. Also, we have developed software that can simultaneously analyze the structure of up to 3 overlapping hyperfine patterns, obtaining accurate centers of gravity and intensities for each. With this new capability, we have determined branching fractions and transition probabilities for about 250 lines of Ho I and we are extending the very incomplete energy level analysis of Ho II. (G. Nave, C. Sansonetti, and J. Reader)

• High Resolution Spectroscopy for Fusion Research and Space Astronomy. To provide data for spectra of medium charged ions of interest for diagnostics of edge regions of tokamak plasmas, we have carried out a new analysis of the spectrum of five-times-ionized zirconium (Zr⁵⁺). Zirconium is a highly refractory material that may play a role in the design of future tokamaks. For this analysis high resolution spectra of Zr were observed with the NIST 10 m vacuum spectrograph in the 15 nm to 250 nm region. The analysis was performed with the aid of atomic structure codes that calculate the expected energy levels and relative intensities of the lines in this region. We determined line identifications for about 400 lines belonging to the excited configurations 4p⁴4d, 5s, 5p, 5d, and 6s. Most of these levels were newly established in this work. We also completed our extensive measurements for singly-ionized mercury, Hg⁺. Along with our previous measurements for other elements they are being used to determine abundances of heavy elements in chemically peculiar stars observed with the Hubble Space Telescope (HST). These data are also applied to better understand properties of the Hg⁺ ion for the development of a highly accurate atomic clock based on trapping Hg⁺ ions in a magnetic trap. (M. Lindsay, C. Sansonetti, and J. Reader)

• Electron-Impact Ionization Cross Sections. Ionization cross sections of atoms and molecules are a critical input in modeling applications in magnetic fusion research, plasma processing of semiconductors, and atmospheric science. The binary-encounter-dipole (BED) model and its simpler version, the binary-encounter-Bethe (BEB) model, has been developed by us to provide accurate ionization cross sections in compact analytic form. The BEB model is the only ab initio theory that can provide reliable ionization cross sections for fairly large molecules such as C₃F₈ and SF₆. During the last year, these theoretical models have been applied to many new molecules, and an updated version of the ionization cross section website, which contains almost 70 molecules, was made public in September. The BED and BEB models were extended to relativistic incident electrons for applications to heavy atoms and inner-shell ionization of light and heavy atoms. The relativistic BEB cross sections for K-shell ionization of light atoms and the total ionization cross sections for heavy rare gases agree well with known experimental results (Fig. 2). For atoms with half-filled electron shells or fewer valence electrons, autoionization of inner orbital excited states - 3s3p³ in Al for example - nearly doubles the total ionization cross section. This discovery resolved a long-standing discrepancy between theory and experiment for Al, Ga, and In. (Y.-K. Kim, P.M. Stone, and M.A. Ali)
  

  Figure 2. Total ionization cross section of Xe. _i = total ionization cross section; T = incident electron energy; BEB = present theory; Wetzel, Nagi, and Nishimura = experiments; gross = total number of electrons produced; count = total number of ions produced.

       

• Data Compilation of Atomic Spectra. Comprehensive tables of the spectra of numerous highly ionized atoms have been published as Monograph 8 of the J. Phys. Chem. Ref. Data and will be soon added to the NIST Atomic Spectra Database on the Web. This data volume contains critically evaluated reference data for about 16 000 transitions from the soft x-ray to the visible spectral regions for most ions of the iron-group elements, as well as Cu, Kr, and Mo. The Monograph should be a valuable resource for fusion energy researchers as well as for astronomers working with the new generation of x-ray space observatories, such as Chandra, XMM-Newton and Astro E, since it contains the largest collection of spectral data available for soft x-ray lines (6000 transitions). We also contributed tables of spectral data of astrophysical interest to a new edition of "Allen's Astrophysical Quantities," a handbook widely used by astronomers. (J. Fuhr, A. Robey, J. Sugar and W.L. Wiese).

• Complex Quantum Nanostructures. Quantum nanostructures are being studied by many labs to realize their promise for enhanced optoelectronic devices, quantum optics, and classical and quantum information processing. We have implemented realistic empirical tight-binding models with Coulomb effects into our theory for quantum dot structures and used these models to study InAs and Si nanoparticles and CdS/HgS and CdS/ZnS quantum dot quantum wells. Our atomistic models allow us to study nanostructures down to the smallest sizes and to consider quantum dot molecules and solids, made by coupling many dots into complex architectures. These complex systems of nanostructures are necessary to provide the practical functionality needed for real devices. Comparison with optical experiments on these systems allows us to provide a detailed understanding of the spectroscopy and optics of these structures. (G.W. Bryant, W. Jaskolski)

• Quantum logic gates with neutral atoms. We have started a new program to simulate quantum logic gates based on neutral atoms in optical lattices. For this purpose it is necessary to develop computational tools for describing the quantum dynamics of two atoms interacting in the presence of an external confining potential. We have developed both grid and configuration interaction methods for calculating the quantum states and time dependent dynamics for such conditions. One specific case we investigated is whether the ground and first excited motional states of an atom in a single optical lattice cell can be used as a quantum bit (or qubit) for logic gate operations. We considered a double-well lattice that could be made using a CO₂ laser and its first harmonic frequency. If a single atom occupies each side of a double well superlattice cell, and the barrier between the two sides is lowered by changing the intensity of one of the lattice lasers, the atom-atom interaction will be conditional on the motional states of the two atoms. We show that logic gates with fidelities greater than 99 % are possible using such a scheme. (C.J. Williams, P.S. Julienne, E. Tiesinga, F.H. Mies, E. Charron)

• Cold Cesium Mysteries Solved. Atomic cesium is an important species that has been the object of numerous cooling and trapping experiments. Laser cooled cesium is the basis of the new NIST F1-cesium atomic fountain clock. In spite of many studies, a quantitative understanding of collisions of cold cesium atoms has proved elusive. It is important to understand these collisions, since collisional shifts in the cesium transition frequency can adversely affect the performance of the fountain clock. In addition, the collisional properties of cesium atoms have prevented the achievement of Bose-Einstein condensation in cold cesium atomic gases. We have constructed a collision model with only four key parameters to characterize the full quantum dynamics of cold cesium collisions. Two of these parameters are known as scattering lengths, which determine clock shifts and the stability of a Bose-Einstein condensate. One is the coefficient that gives the magnitude of the long-range force between the two atoms. The other expresses the effective interaction between the two electron spins as modified by chemical bonding effects in the cesium dimer molecule. The four model parameters were determined by analyzing new experiments at Stanford University that use a magnetic field to tune a number of cesium dimer bound states to be in resonance with the colliding atoms. The resulting quantitative model not only accounted for all previously existing data on ground state cold cesium atom collisions but also accurately predicted locations for a number of resonances in the Stanford experiment prior to measurement. The new model, contrary to previous expectations, predicts that the collisional shift in a cesium fountain clock could be greatly reduced if the clock could be operated at a much lower temperature in the range of 50 nanokelvin. The model also makes specific predictions of magnetic field strengths for which Bose-Einstein condensation of cesium might be possible. (P.S. Julienne, C.J. Williams, P. Leo)

• Theory of Nanooptics. Detailed modeling of nanooptics is needed to provide the theoretical foundation for imaging and metrology with near-field scanning optical microscopy (NSOM) and for near-field optical interaction and optical manipulation of matter. We have continued development of our coupled dipole method and implementation of finite-difference time domain and finite element methods for nanooptics modeling. Our simulations show how NSOM can provide nanoscale local optical metrology of optical waveguides. Our modeling of recent NSOM measurements on semiconductor photonic crystals reveals how multiple scattering and interference critically affect image contrast. Nanooptics modeling applied to optical waveguides shows that the evanescent near-fields outside the guides can be used to trap and manipulate atoms. This raises the possibility of using complex waveguide structures in applications, such as quantum computing and single-atom chemistry, where controlled coherent atom manipulation is critical. The local optics of sources in nanocavities has been modeled to show how optical near-fields can be engineered to tailor optical coupling to and between nanostructures. (G.W. Bryant, P.S. Julienne, J. Burke, A. Rahmani, S.-T. Chu, R. Owen)

• Trapped-Ion Dynamics Studied in EBIT. EBIT facilities, now in operation or under construction at nearly a dozen locations around the world, use ion-trapping techniques to enable new studies in atomic physics and nano-scale surface science. Although the first such facilities have been in operation for over a decade, virtually no data is available concerning the actual spatial distribution and dynamical motion of the ions inside the traps. Previous knowledge of this sort has either been inferred from indirect measurements or was based on complicated models of ion production, loss and interaction. We have now used a sensitive CCD camera to directly image highly charged ions inside our EBIT, study their dynamical motion, and determine the thermal distribution within the trap. The results have been combined with modeling efforts in order to more accurately describe the ion behavior within the trap. In addition to being a valuable tool to aid experiments in the two areas of atomic physics and ion-surface studies, the ion imaging work opens up a third area of inquiry with EBITs that is interesting in its own right. The dynamics of highly charged ion clouds in the combined electric and magnetic fields of an EBIT provide information about a variety of physical processes such as cross-field diffusion and electron-ion heating rates within plasmas. In addition, with knowledge gained from these studies it should be possible to dramatically cool the ions, allowing for the study and control of dense, highly charged ion clouds. Related long-term applications involving the manipulation of trapped highly charged ions to realize quantum computing schemes have already been discussed. (J.D. Gillaspy, J.V. Porto, and I. Kink).

• GEC-ICP RF Plasma Source. High-density, low-pressure plasma sources are being widely used to meet the demands of reducing the critical dimensions of etched structures in the semiconductor industry. As the wafer diameters used in etching increase, monitoring and control of plasma uniformity also becomes increasingly important. In order to address these issues, a new type of fiber optic based optical tomography sensor has been developed. Optical tomography derives the two-dimensional distribution of species in a plasma from multiple optical emission measurements without assuming a radially symmetric plasma. This new sensor simultaneously acquires optical emission measurements from 82 different directions through two small windows in less than a second. One initial application of the sensor was to demonstrate the influence of a quartz confinement ring in the GEC-ICP plasma source, which is used to increase the stable operating range of electronegative plasmas. The confinement ring reduces the effective radius and improves the radial symmetry of the discharge. In order to more effectively utilize the data obtained from the sensor, we have also developed a new type of inversion algorithm to convert the optical signals into the actual plasma distribution. This new algorithm has been designed to operate on a desktop computer and combines an algebraic recombination technique (ART) with a curve fitting algorithm to provide the necessary smoothing to the inversion process. (E. Benck and K. Etamadi)

• Key Progress on 157 nm Lithography Materials. We exploited our high-accuracy UV index of refraction measurement capabilities to solve a key materials issue in the development of 157 nm optical lithography, which has been embraced by the semiconductor microelectronics industry as the technology to enable integrated circuit critical-feature-sizes to 100 nm and below. Though initial production with this technology has been projected to begin around 2003, a potential show-stopping problem has been the lack of a second UV material that could be combined with calcium fluoride in the optics to correct for chromatic aberrations, due to the finite band width of the 157 nm excimer laser illumination source. Using the facilities that enabled us to determine the first accurate measurements of the index properties of calcium fluoride at 157 nm, we surveyed the index properties of the most promising candidate second materials. On the basis of our 157 nm index, index dispersion, and thermal coefficient measurements, we established that barium fluoride well satisfies the criteria for a color-correcting second material. This result demonstrated the feasibility of all-refractive 157 nm lithography systems. Based on these measurements, all-refractive 157 nm lithography system designs using combined calcium fluoride and barium fluoride optics are now being pursued by the major lithography companies. (J.H. Burnett, U. Griesmann, with R. Gupta, Div 844).

• Nanoscale features created with highly charged ions. It has been shown that impacts of slow, very highly charged ions (for example Xe⁴⁴⁺) create nanoscale protrusions on mica surfaces. Furthermore, the size of these features increases rapidly as the charge state (and therefore the potential energy) is increased, but is insensitive to changes in the projectile kinetic energy over a large range. In all of these studies, the ion-bombarded surfaces were imaged in air, allowing the possibility that the ion-induced features are modified by atmospheric contamination. Such contamination could drastically alter the morphology of these features. The goal of the present work was to image highly charged ion-induced features in such a way that the observations reflect, as closely as possible, the morphology of the surface as formed by the ion impacts. This will allow us to better understand the nature of these features, and ultimately, the mechanism of their creation. To that end, our experiments were performed in vacuum, imaging the ion-bombarded mica with AFM (atomic force microscopy), before they were exposed to air. The observed features are protrusions, and their diameter is about 20 nm. Our measured heights are larger than those that have been measured previously in air. Also, we do not find that the features are modified after repeated AFM scanning as was previously observed when imaging with AFM in air. We interpret these differences as being due to water that is adsorbed when the samples are in air. The capillary forces due to this water layer increase the force between the sample and the probe, possibly deforming the surface. Therefore, the new images, which were taken in vacuum, are more likely to reflect the true morphology of the features as created by the highly charged ion impacts. This improved understanding of the morphology of these features is a step toward understanding the physical mechanisms that underlie their creation. (L.P. Ratliff, R. Minniti, and J.D. Gillaspy).

• EBIT Used to Simulate Cosmic Plasmas for Quantum Calorimeters. The Chandra x-ray observatory, launched into orbit by NASA in 1999 after more than 15 years of planning, was designed to revolutionize astronomy by providing an unprecedented view of the universe. With 100 times the sensitivity of previous x-ray telescopes as well as much higher resolution, the multi-billion dollar Chandra is now producing such high quality data that it is challenging the ability of astrophysicists to interpret it. Furthermore, one of NASA's top priority scientific missions for the next decade is Constellation X, an even more powerful orbiting array of x-ray instruments based on quantum calorimetry. In support of these present and future missions, we are working with scientists from the Harvard-Smithsonian Center for Astrophysics and the Naval Research Laboratory to improve the understanding of fundamental processes occurring in hot cosmic plasmas, and to test quantum calorimeters at our EBIT facility. Ion temperatures in excess of ten million degrees Kelvin are readily achieved with our EBIT, under conditions that can be precisely controlled to sort out the dependencies of key diagnostic x-ray lines on density, temperature, and other excitation conditions. We have now recorded detailed spectra from half a dozen highly ionized species, including the particularly relevant case of iron. The measurements in iron were repeated at half a dozen different electron beam energies in order to unravel the temperature dependence of the line intensities. We have analyzed the spectra to provide quantitative tests of the models used to interpret astrophysical plasmas. In some cases we find good agreement, and in other cases we find that the existing models give erroneous results. We are working to include more physics in the models in order to improve the agreement. (J.D. Gillaspy, E. Takacs, I. Kink, and J.V. Porto).

• Ultracold Collisions. Using one laser to photoassociate slowly colliding atoms into bound states of excited diatomic molecules, we then use further lasers to take these molecules into either doubly-excited states or to bound ground-state molecules. New spectroscopy of the 0_g^- (S+P_1/2) state and several doubly-excited states in Na₂ has been obtained. Spectra of several never-before seen states in the triplet ground state of Na₂ have also been obtained. In particular, we have observed v = 12-15 (the last four triplet bound states) and we are devising ways in which we might extend these measurements down to v = 0. We have also detected the stable formation of triplet ground state Na₂ molecules, created by spontaneous emission from an excited state. Optical Feshbach resonances have been observed and their effects on the scattering properties of cold atoms measured. This technique could represent a new way to modify the scattering length in Bose-Einstein condensates. (F. Fatemi, K. Jones, P. Lett)

• Ultracold Plasmas. In the laser-cooled xenon experiment, we have continued to study ultracold plasmas created by photoionization. We have produced the coldest neutral plasma ever created, with electron temperatures as low as 1 K and ion temperatures that are much lower. We developed a simple model to explain the plasma creation, and found excellent quantitative agreement with experimental results. We have excited a collective mode, the plasma oscillation, and used it to monitor the time-dependent density of the expanding, unconfined plasma. We found an expansion rate dominated by the pressure the electrons exert on the ions, and find good agreement with a hydrodynamic model at high (>100 K) temperatures. At low temperatures and high densities, we find an anomalously large expansion rate, which is currently under study, and is believed to be due to electron-ion correlations. (R. Dumke, T. Killian, M. Lim, S. Rolston)

• Optical tweezers. We have developed a technique, using optical tweezers, to measure stochastically-driven on and off rates of adhesion to biomolecules immobilized on surfaces. We have measured the distribution of times for formation and dissociation of antigen-antibody bonds and initiated theoretical modeling of the experimental results. We have constructed a new apparatus incorporating both optical tweezers and an "optical scalpel" to cut into biological objects. We have now initiated studies of liposome manipulation using both the optical tweezers and scalpel. We have also begun construction of a new apparatus for microassembly of mechanical structures using optical tweezers. With this apparatus we have demonstrated 3-D trapping of micron-sized gold particles in single-focus optical tweezers. These trapped particles are far larger than any reflective particles that have been previously reported being trapped, and the trapping mechanism is not understood theoretically. (J. Hall, K. Helmerson, R. Kishore, S. Kulin)

• Optical Interactions in Bose-Einstein Condensates. We have demonstrated the adiabatic loading of condensate atoms into the ground state of a 1-D optical lattice and the coherent transfer of these atoms into higher-band states. Such experiments are important to evaluate the possibility of using neutral atoms held in off-resonant optical lattice potentials for quantum manipulation and information processing. Recently we have also begun to measure the loss rates of atoms from a BEC due to photoassociation and compare these rates with theoretical predictions. We have developed an interferometric method of spatially imaging the phase of a BEC, and used the method to study the expansion of the condensate driven by the mean-field interactions. We confirmed the theoretical predictions of a quadratic phase variation across the condensate and made the first direct observation of mean-field repulsion between two condensate clouds. (D. Cho, J. Denschlag, K. Helmerson, F. Fatemi, J. Simsarian, K. Jones, P. Lett, W. Phillips, S. Rolston, P. Julienne, C. Williams, E. Tiesinga)

• Atom Optics. We have measured the coherence length, or coherence time, for atoms outcoupled from our BEC. By implication, this gives us information about the coherence of the parent condensate. For the case of a condensate that has the output coupling applied with the trapping potential on, we find that we have the full expected coherence. When we release the condensate before coupling out the wavepackets, we find that the coherence is reduced because the mean-field expansion produces a phase gradient across the condensate. Our investigations of Bose condensates have inaugurated the new discipline of "nonlinear atomic optics." Soon after the prediction and achievement of four-wave mixing in these systems at NIST, another fundamental manifestation of nonlinear materials -- the propagation of solitons -- was also observed in trapped condensates. Solitons are localized traveling waves that preserve their spatial profile due to a balance between the wave dispersion and the nonlinearity of the medium. In confined geometries such as optical fibers, solitons of light can propagate long distances (hundreds of meters) without decaying. In an interacting Bose condensate, the solitons appear as dark kinks that travel more slowly than the speed of sound. The experiment was substantially motivated by our theoretical studies initiated in 1997. These studies found that, for condensates with repulsive interactions, solitons could be generated by imposing gradients in the phase of the condensate wavefunction. In our experiments the condensate is exposed to a spatially inhomogeneous light field, which induces a local variation of phase that is proportional to the value of the AC Stark shift. We obtain very good agreement between computational solutions of the Gross-Pitaevskii equation and the experiments (as shown in Fig. 3). Indeed, the calculations (performed by collaborating groups in Electron and Optical Physics Division) are essential for interpreting the combination of soliton and phonon modes produced in the experiments. (J. Denschlag, K. Helmerson, W. Phillips, J. Simsarian, S. Rolston, with D. Feder and C. Clark, Div. 841)
  

  Figure 3. Experimental (top row) and theoretical (bottom row) propagation of a soliton in the Bose condensate. A positive density wave moves in the +x direction at the speed of sound, and a dark soliton moves in the opposite direction with a speed less than that of sound. Since the imaging technique destroys the condensate, each image shows a different condensate.

• Quantum Computing. We have recently begun an experimental effort to investigate quantum information processing using neutral atoms. We have begun to build-up a new lab in which rubidium atoms will be cooled and trapped and made to form a Bose-Einstein condensate. These atoms will then be loaded into a 3-D optical lattice for manipulation with the goal of investigating quantum gates for quantum information processing. In recent experiments using our existing sodium BEC we have demonstrated the adiabatic loading of condensate atoms into the ground state of a 1-D optical lattice and the coherent transfer of these atoms into higher-band vibrational states. (K. Helmerson, B. King, P. Lett, S. Peil, W. Phillips, S. Rolston)

• International Workshop on Gamma-Ray Spectroscopy featured in NIST Journal of Research. The January-February 2000 issue of the NIST Journal of Research was devoted to the proceedings of an International Workshop on High Resolution Gamma-Ray Spectroscopy and Applications. The guest editors for this special issue are Professor A. Aprahamian of Notre Dame and Dr. R.D. Deslattes of the NIST Physics Laboratory. Most contributions to the workshop were based on work carried out at the High Flux Reactor of the Institut Laue-Langevin (ILL) in Grenoble, France, using the ultra-high resolution crystal diffraction spectrometer GAMS4. The spectrometer was designed and built at NIST and is currently operated as a joint ILL-NIST facility in a program led by E. Kessler of NIST and H. Börner of ILL. This program not only addresses issues of importance to NIST and the ILL but also serves the needs of users from a variety of disciplines, all of which are represented in contributions to this special issue. The distinctive features of GAMS4 are its accuracy and its exceptionally high spectroscopic resolving power. The accuracy achieved has been an essential contributor to NIST work on the properties of fundamental particles, the determination of fundamental constants, and gamma-ray energy standards. The exceptional resolution capability is exploited for the determination of nuclear excited state lifetimes between the picosecond and femtosecond levels. In the course of modeling these spectra, significant information has emerged on the form of the interatomic potential function in the range 10 eV to 100 eV, a region not accessible by other means. Since its installation in the mid-80's, the GAMS4 collaboration has been a model of productive international cooperation. (R. Deslattes and E. Kessler)

• Si SRM-640c certified and released for sale. Standard Reference Material (SRM) 640c, a silicon powder standard, was released to the scientific and industrial community in September 2000. This SRM is intended for use as a standard for calibration of diffraction line positions and line shapes, determined through powder diffractometry. NIST is the world's principal source of powder-diffraction reference materials that are used as standards in crystal structural investigations. SRM-640c replaces SRM-640b whose reserve was depleted and whose certification was inadequate for the more advanced powder diffraction structural determinations. The production and certification of SRM-640c was a collaboration between the Materials Science and Engineering Laboratory and the Physics Laboratory. We verified the uniformity of the single-crystal silicon starting material and developed a diffractometer for first principles lattice parameter measurements which are linked to the International System of Units (SI) through the wavelength of the Cu K radiation. In addition, we collected all the data from random samples of the 640c powder. The relative uncertainty of the lattice parameter is 1.7 x 10^-6 (95 % confidence limit). (J.L. Staudenmann, L. Hudson, R. Deslattes, and E. Kessler)

High Energy X-ray Spectrometer (HXS) successfully installed at OMEGA. The Division fielded a curved-crystal spectrometer system at the University of Rochester's Laboratory for Laser Energetics (LLE). There it will be used as a core diagnostic to study the plasmas produced by the OMEGA laser by acquiring x-ray spectra in the energy range of 12 keV to 60 keV. The spectrometer was designed, built, and calibrated at NIST, and the backplane sensor and drive electronics were provided by collaborators from the Naval Research Laboratory. Recently, these two halves of the HXS system were mated and tested at NIST using a microfocus x-ray source to mimic the direct-drive targets that will be studied at LLE. Initial field testing registered high-resolution CCD spectra from individual 1 ns laser shots (60 convergent beams totaling around 23 kJ of energy) of krypton-filled CH targets. First results, shown below, measured the variability of the first resonance lines of highly charged Kr under different plasma conditions. The ratio of He- to Li-like Kr signals as well as the slope of the continuum can be used to derive the electron temperature of the plasmas created. (L. Hudson)

Figure 4. Highly-charged krypton spectra from three shots (numbered) of the OMEGA laser exciting plasmas with decreasing electron temperature.       In spectra from the lower energy laser shots, signatures from lower-charge-state species become more apparent.

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"Technical Activities 2000" - Table of Contents