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Electrons in graphene are described by relativistic Dirac Weyl spinors with a two-component pseudospin. The unique pseudospin structure of Dirac electrons leads to emerging phenomena such as the massless Dirac cone, nomalous quantum Hall effect, and Klein tunnelling, in graphene. The capability to manipulate electron pseudospin is highly desirable for novel graphene electronics, and it requires precise control to differentiate the two graphene sublattices at the atomic level. Graphene/boron nitride moir superlattices, where a fast sublattice oscillation due to boron and nitrogen atoms is superimposed on the slow moire period, provides an attractive approach to engineer the electron pseudospin in graphene., Published in Nature Physics, v10 p743-747, October 2014.

Relativistic quantum mechanics predicts that when the charge of a super-heavy atomic nucleus surpasses a certain threshold, the resulting strong Coulomb field causes an unusual atomic collapse state which exhibits an electron wave function component that falls toward the nucleus as well as a positron component that escapes to infinity. In graphene, where charge carriers behave as massless relativistic particles, it has been predicted that highly charged impurities should exhibit resonances corresponding to these atomic collapse states. We have observed the formation of such resonances around artificial nuclei (clusters of charged calcium dimers) fabricated on gated graphene devices via atomic manipulation with a scanning tunneling microscope (STM). The energy and spatial dependence of the atomic collapse state measured using STM revealed unexpected behavior when it is occupied by electrons., Published in Sciencexpress, 7 Mar 2013. Prepared in collaboration with the Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, the School of Physics, University of Exeter, UK, the Department of Physics, Massachusetts Institute of Technology, Cambridge, and the Department of Physics and Astronomy, University of California, Riverside.

Graphene has extremely low mass density and high mechanical strength, and key qualities for efficient wide-frequency-response electrostatic audio speaker design. Low mass ensures good high frequency response, while high strength allows for relatively large free-standing diaphragms necessary for effective low frequency response. Here, we report on construction and testing of a miniaturized graphene-based electrostatic audio transducer. The speaker/earphone is straightforward in design and operation and has excellent frequency response across the entire audio frequency range (20 Hz 20 kHz), with performance matching or surpassing commercially available audio earphones, Published in Applied Physics Letters, v102 p223109-1/223109-5, 2013.

For many types of superconducting qubits, magnetic flux noise is a source of pure dephasing. Measurements on a representative dc superconducting quantum interference device (SQUID) over a range of temperatures show that S(phi)(f) = A(2)/(f/1 Hz)(alpha), where S(phi) is the flux noise spectral density, A is of the order of 1 micron/phi(0) Hz(-1/2), 0.61 is less than or equal to alpha less than or equal to 0.95, and phi(0) is the flux quantum. For a qubit with an energy level splitting linearly coupled to the applied flux, calculations of the dependence of the pure dephasing time Tau(phi) of Ramsey and echo pulse sequences on alpha for fixed A show that Tau(phi) decreases rapidly as alpha is reduced. We find that Tau(phi) is relatively insensitive to the noise bandwidth, f(1) is less than or equal to f less than or equal to f2, for all alpha provided the ultraviolet cutoff frequency f2 greater than 1/Tau(phi). We calculate the ratio Tau(phi), Epsilon/Tau(phi), R of the echo (epsilon) and Ramsey (R) sequences and the dependence of the decay function on alpha and f2. We investigate the case in which S(phi) (f0) is fixed at the pivot frequency f0 not equal to 1 Hz while alpha is varied and find that the choise of f0 can greatly influence the sensitivity of Tau(phi), Epsilon and Tau(phi), R to the value of alpha. Finally, we present calculated values Tau(phi) in a qubit corresponding to the values of A and alpha measured in our SQUID., Published in Physical Review, v85 n22 p224505/1-6, 2012. Sponsored in part by ODNI and IARPA.

Surface plasmon has the unique capability to concentrate light into subwavelength volume. Active plasmon devices using electrostatic gating can enable flexible control of the plasmon excitations,6 which has been demonstrated recently in terahertz plasmonic structures. Controlling plasmon resonance at optical frequencies however, remains a significant challenge because gate-induced free electrons have very weak responses at optical frequencies. Here we achieve efficient control of nearinfrared plasmon resonance in a hybrid graphene-gold nanorod system. Exploiting the uniquely strong and gate-tunable optical transitions of graphene, we are able to significantly modulate both the resonance frequency and quality factor of gold nanorod plasmon. Our analysis shows that the plasmon-graphene coupling is remarkably strong: even a single electron in graphene at the plasmonic hotspot could have an observable effect on plasmon scattering intensity. Such hybrid graphene-nanometallic structure provides a powerful way for electrical control of plasmon resonances at optical frequencies and could enable novel plasmonic sensing down to single charge transfer events., Published in Nano Letters, v12 p5598-5602, 2012.

The efficient conversion of an electrical signal to an optical signal in nanophotonics enables solid state integration of electronics and photonics. The combination of graphene with photonic crystals is promising for electro-optic modulation. In this paper, we demonstrate that by electrostatic gating a single layer of graphene on top of a photonic crystal cavity, the cavity resonance can be changed significantly. A 2 nm change in the cavity resonance line width and almost 400% (6 dB) change in resonance reflectivity is observed. In addition, our analysis shows that a graphene photonic crystal device can potentially be useful for a high speed and low power absorptive and refractive modulator, while maintaining a small physical footprint., Published in Nano Letters, 2012. Prepared in collaboration with the E. L. Ginzton Laboratory, Stanford University, Stanford, CA, and the Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA. Sponsored in part by DoE DE-AC02-05CH11231.

Photovoltaics (PV) are a promising source of clean renewable energy, but current technologies face a cost-to-efficiency trade-off that has slowed widespread implementation. We have developed a PV architecture--screening-engineered field-effect photovoltaics (SFPV)--that in principle enables fabrication of low-cost, high efficiency PV from virtually any semiconductor including the promising but hard-to-dope metal oxides, sulfides, and phosphides. Prototype SFPV devices have been constructed and are found to operate successfully in accord with model predictions., Published in Nano Letters, 2012. Sponsored in part by DoE.

Boron nitride nanoribbons (BNNRs), the boron nitride structural equivalent of graphene nanoribbons (GNRs), are predicted to possess unique electronic and magnetic properties. We report the synthesis of BNNRs through the potassium-intercalation-induced longitudinal splitting of boron nitride nanotubes (BNNTs). This facile, scalable synthesis results in narrow (down to 20 nm), few sheet (typically 2-10), high crystallinity BNNRs with very uniform widths. The BNNRs are at least 1 micro m in length with minimal defects within the ribbon plane and along the ribbon edges., Published in Nano Letters, v11 p3221-3226, 24 May 2011. Sponsored in part by AFRL, ONR, DoE DE-AC02-05CH11231 and NSF EEC-0425914.

Plasmons describe collective oscillations of electrons. They have a fundamental role in the dynamic responses of electron systems and form the basis of research into optical metamaterials. Plasmons of two-dimensional massless electrons, as present in graphene, show unusual behaviour that enables new tunable plasmonic metamaterials and, potentially, optoelectronic applications in the terahertz frequency range. Here we explore plasmon excitations in engineered graphene microribbon arrays. We demonstrate that graphene plasmon resonances can be tuned over a broad terahertz frequency range by changing micro-ribbon width and in situ electrostatic doping. The ribbon width and carrier doping dependences of graphene plasmon frequency demonstrate power-law behaviour characteristic of two-dimensional massless Dirac electrons. The plasmon resonances have remarkably large oscillator strengths, resulting in prominent room-temperature optical absorption peaks. In comparison, plasmon absorption in a conventional two-dimensional electron gas was observed only at 4.2 K. The results represent a first look at light plasmon coupling in graphene and point to potential graphene-based terahertz metamaterials., Published in Nature Nanotechnology, v6 p630-634, Oct 2011. Sponsored in part by DoE DE-AC02-05CH11231.

Inelastic light scattering spectroscopy has, since its first discovery been an indispensable tool in physical science for probing elementary excitations, such as phonons,magnons and plasmons in both bulk and nanoscale materials. In the quantum mechanical picture of inelastic light scattering, incident photons first excite a set of intermediate electronic states, which then generate crystal elementary excitations and radiate energy-shifted photons. The intermediate electronic excitations therefore have a crucial role as quantum pathways in inelastic light scattering, and this is exemplified by resonant Raman scattering and Raman interference. The ability to control these excitation pathways can open up new opportunities to probe, manipulate and utilize inelastic light scattering. Here we achieve excitation pathway control in graphene with electrostatic doping. Our study reveals quantum interference between different Raman pathways in graphene: when some of the pathways are blocked, the one-phonon Raman intensity does not diminish, as commonly expected, but increases dramatically. This discovery sheds new light on the understanding of resonance Raman scattering in graphene. In addition,we demonstrate hot-electron luminescence in graphene as the Fermi energy approaches half the laser excitation energy. This hot luminescence, which is another form of inelastic light scattering, results from excited-state relaxation channels that become available only in heavily doped graphene., Published in Nature, v471 p617-620, 31 Mar 2011. Sponsored in part by DoE DE-AC02-05CH11231 and DE-AC02-05CH11231.

Chemical vapor deposited (CVD) graphene is often presented as a scalable solution to graphene device fabrication, but to date such graphene has exhibited lower mobility than that produced by exfoliation. Using a boron nitride underlayer, we achieve mobilities as high as 37 000 cm(expn 20)/ V s, an order of magnitude higher than commonly reported for CVD graphene and better than most exfoliated graphene. This result demonstrates that the barrier to scalable, high mobility CVD graphene is not the growth technique but rather the choice of a substrate that minimizes carrier scattering., Published in Applied Physics Letters, v98 article no. 242105, 13 Jun 2011. Sponsored in part by DoE.

The use of boron nitride (BN) as a substrate for graphene nanodevices has attracted much interest since the recent report that BN greatly improves the mobility of charge carriers in graphene compared to standard SiO2 substrates. We have explored the local microscopic properties of graphene on a BN substrate using scanning tunneling microscopy. We find that BN substrates result in extraordinarily flat graphene layers that display microscopic Moir e patterns arising from the relative orientation of the graphene and BN lattices. Gate-dependent dI/dV spectra of graphene on BN exhibit spectroscopic features that are sharper than those obtained for graphene on SiO2. We observe a significant reduction in local microscopic charge inhomogeneity for graphene on BN compared to graphene on SiO2., Published in Nano Letters, v11 p2291-2295, 9 May 2011. Sponsored in part by DoE and NSF DMR-0906539.

We have fabricated and tested large scale arrays of Josephson junctions. Some devices have as many as 150,000 junctions in a single device. To aid in device design we have also developed a numerical simulation program in Matlab to simulate voltage magnetic field characteristics for these arrays. Our numerical simulation code supports the modeling of 2 dimensional array structures and takes into account mutual interactions between all of the squids in the array. The results are in excellent agreement with our experimental measurements. We have also performed measurements of the critical current noise in our Josephson junctions and have been testing arrays in flux locked loops.

We report what we believe is the first experimental limit placed on plant biomagnetism. Measurements with a sensitive atomic magnetometer were performed on the Titan arum (Amorphophallus titanum) inflorescence, known for its fast biochemical processes while blooming. We find that the magnetic field from these processes, projected along the Earth s magnetic field, and measured at the surface of the plant, is 0.6 muG., Published in Journal of Applied Physics, v109 p074701-1/074701-5, 2011.

Recent theoretical proposals suggest that strain can be used to engineer graphene electronic states through the creation of a pseudo magnetic field. This effect is unique to graphene because of its massless Dirac fermion-like band structure and particular lattice symmetry (C[sub 3v]). Here, we present experimental spectroscopic measurements by scanning tunneling microscopy of highly strained nanobubbles that form when graphene is grown on a platinum (111) surface. The nanobubbles exhibit Landau levels that form in the presence of strain-induced pseudo magnetic fields greater than 300 tesla. This demonstration of enormous pseudo magnetic fields opens the door to both the study of charge carriers in previously inaccessible high magnetic field regimes and deliberate mechanical control over electronic structure in graphene or so-called strain engineering., Published in Science, v329 p544-547, 30 Jul 2010. Prepared in collaboration with the Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, Instituto de Ciencia de Materiales de Madrid, Spain, and the Department of Physics, Boston University, MA.

We demonstrate a process for batch production of large-area (100-3000 sq microns) patterned freestanding graphene membranes on Cu scaffolds using chemical vapor deposition (CVD)-grown graphene. This technique avoids the use of silicon and transfers of graphene. As one application of this technique, we fabricate transmission electron microscopy (TEM) sample supports. TEM characterization of the graphene membranes reveals relatively clean, highly TEM-transparent, single-layer graphene regions ( 50% by area) and, despite the polycrystalline nature of CVD graphene, membrane yields as high as 75-100%. This high yield verifies that the intrinsic strength and integrity of CVD-grown graphene films is sufficient for sub-100 m width membrane applications. Elemental analysis (electron energy loss spectroscopy (EELS) and X-ray energy-dispersive spectroscopy (EDS)) of the graphene membranes reveals some nanoscaled contamination left over from the etching process and we suggest several ways to reduce this contamination and improve the quality of the graphene for electronic device applications. This large-scale production of suspended graphene membranes facilitates access to the two-dimensional physics of graphene that are suppressed by substrate interactions and enables the widespread use of graphene-based sample supports for electron and optical microscopy., Published in ACA Nano, v4 n8 p4762-4768, 2010.

A facile method is reported for the direct (polymer-free) transfer of layer-area graphene from metal growth substrates to selected target substrates. The direct route, by avoiding several wet chemical steps and accompanying mechanical stresses and contamination common to all presently reported layer-area graphene transfer methods, enables fabrication of layer-area graphene devices with unprecedented quality. To demonstrate, we directly transfer layer-area graphene from Cu growth substrates to holey amorphous carbon transmission electron microscopy (TEM) grids, resulting in robust, clean, full-coverage graphene grids ideal for high resolution TEM., Published in Applied Physics Letters, v96 p113102-1/113102-3, 2010.

Electrons moving in graphene behave as massless Dirac fermions, and they exhibit fascinating low-frequency electrical transport phenomena. Their dynamic response, however, is little known at frequencies above one terahertz (THz). Such knowledge is important not only for a deeper understanding of the Dirac electron quantum transport, but also for graphene applications in ultrahigh speed THz electronics and IR optoelectronics. In this paper, we report the first measurement of high-frequency conductivity of graphene from THz to mid-IR at different carrier concentrations. The conductivity exhibits Drude-like frequency dependence and increases dramatically at THz frequencies, but its absolute strength is substantially lower than theoretical predictions. This anomalous reduction of free electron oscillator strength is corroborated by corresponding changes in graphene interband transitions, as required by the sum rule. Our surprising observation indicates that many-body effects and Dirac fermion-impurity interactions beyond current transport theories are important for Dirac fermion electrical response in graphene., Performed in cooperation with Fudan University, Shanghai, China; and Lawrence Berkely National Laboratory, Berkely, CA. Sponsored in part by Department of Energy contracts DE-AC02-05CH11231, DE-AC03-76SF0098, and DE-AC02-05CH11231.

We present transport measurements of unshunted dc superconducting quantum interference devices (SQUIDs) consisting of 30 nm wide aluminum nanobridges of varying length L contacted with two and three dimensional banks. 3D nanobridge SQUIDs with L less than or equal to 150 nm (approximately 3-4 times the superconducting coherence length) exhibit approx. 70% critical current modulation with applied magnetic field, approaching the theoretical limit for an ideal short metallic weak link. In contrast, 2D nanobridge SQUIDs exhibit significantly lower critical current modulation. This enhanced nonlinearity makes 3D nanobridge Josephson junctions well suited to optimize sensitivity in weak link SQUID magnetometers as well as realize ultra low-noise amplifiers and qubits.

A new experimental platform for studies of transport and quantum-limited measurements of cold, trapped atomic gases was constructed. Using microfabrication processes, a silicon wafer was micromachined to allow for deposition of micrometer-scale electromagnet wires and for the integration of closely spaced, highly reflective optical mirrors. With this device, nanokelvin-temperature atomic gases were produced and placed with nanometer precision within a high-finesse optical resonator, and to construct a cavity optomechanical system with ultracold atomic gases, with the goals of understanding how to conduct quantum-limited measurements of the motion of a macroscopic mechanical object and characterizing the new phenomena arising in such a hybrid optomechanical quantum system. Key results include the tuning between linear and quadratic optomechanical regimes, allowing one to measure either the displacement or the strain of a compressible cantilever; the first characterization of optomechanical effects in the quadratic coupling regime; and quantitative matching between experimental observations and simple theoretical predictions that establish the validity of this innovative use of cold atomic gases.

We show by pump-probe spectroscopy that the optical response of a fishnet metamaterial can be modulated on the femtosecond time scale. The modulation dynamics is dominated by pump-induced changes in the constituting dielectric medium, but the strength of modulation is dramatically enhanced through the plasmon resonance. The pump-induced spectral responses of the metamaterial provide understanding on how the resonance is modified by pump excitation. Our study suggests that metamaterials can be used as high-speed amplitude/phase modulators with terahertz-bandwidth., Published in the OPTICS EXPRESS, v17 n20 p17652-17657, 2009. Prepared in cooperation with Hewlett-Packard Laboratories, Palo Alto, California, and with Lawrence Berkeley Laboratory, Berkeley, California.

The overall objective of this seedling grant was to integrate high-finesse optical cavities onto atom chips so as to advance the application of cavity quantum electrodynamics (CQED) to ultracold atoms for applications in sensing quantum information technology exploration and basic science. We have accomplished all of the experimental objectives for this project. Extensive research and testing of various microfabrication methods yielded a robust recipe for integrating small-scale high-finesse mirrors onto sapphire and glass substrates. The challenges of temperature variations on and vibrational coupling to the chip were addressed effectively. We fabricated a sapphire-substrate atom chip with integrated Fabry-Perot cavity and a temperature stabilization system. The high-finesse cavity achieving the single-atom strong-coupling regime for rubidium atoms, and was kept locked during a simulated operation of the atom chip.

Atmospheric density fluctuations which affect 'seeing' have been studied to examine details of their characteristics and ways of at least partial compensation. Work involved two 60 ft erectable masts, each with five fast temperature sensors, and also measuring equipment set up on a pole at a height of 160 feet on the top of a rather narrow 160 ft building. Wind speed measuring equipment was also installed. Extensive data has been taken as a function of height, horizontal separation, wind speed, and time of day. It has been found that the Kolmogorov-Taylor approximation has validity, but that there are important deviations from it. The power law of fluctuations as a function of frequency devices somewhat from this KT model. The Taylor approximation for movement of fluctuations by wind is a reasonable approximation for modest distances but the time length of its validity is no longer than about 13 seconds. Major turbulences are shown to have similar vertical and horizontal sizes, and to vary in size approximately linearly with wind speed. Correction of approximately one half of the path length fluctuations of light passing through the earth's atmosphere appear to be possible from measurements monitoring fluctuations near the earth's surface.

The decay of the diocotron rotation was studied in a new regime in which trap asymmetries dominate. The decay does not conserve angular momentum, and is strongest for small, low-density columns. For such columns decay of the diocotron mode within few diocotron periods was observed, orders of magnitude faster than the rotational pumping prediction. However, transition to decay dominated by rotational pumping was observed for larger and denser columns. The new regime is characterized by magnetron-like" rotation in the trap, dominated by the end confinement fields. The asymmetry-dominated transport was also studied, and found to depend linearly on the line density (and not the density) over nearly 4 orders of magnitude., This article is from CP606, Non-Neutral Plasma Physics IV, p422-432, 2001. Pub. in AIP Conference Proceedings: volume 606. Prepared in cooperation with Ernst-Moritz-Arndt-Universitaet, Greifswald, Germany; NRCN Beer Sheva, Israel. This article is from ADA404831 Non-Neutral Plasma Physics 4. Workshop on Non-Neutral Plasmas (2001) Held in San Diego, California on 30 July-2 August 2001

We performed experiments with electrons in a Malmberg-Penning trap, as well as 2D fluid simulations, and found conditions that lead to off-axis equilibrium states. We found that unstable initial distributions whose average distance from the axis is larger than about half the wall radius end up in off-axis states. These states consist of a small strong vortex and a large diffuse background, each having about half of the initial charge. We present a simple model showing that for small initial distributions, on-axis solutions maximize the background radius and thus the entropy. For extended initial distributions, no on-axis solutions are available and staying off-axis is necessary for the conservation of angular momentum, This article is from CP606, Non-Neutral Plasma Physics IV, p433-439, 2001. Pub. in AIP Conference Proceedings: volume 606. Prepared in cooperation with Ernst-Moritz-Arndt-Universitaet, Greifswald, Germany; NRCN, Beer Sheva, Israel; West Virginia Univ. Morgantown, WV. This article is from ADA404831 Non-Neutral Plasma Physics 4. Workshop on Non-Neutral Plasmas (2001) Held in San Diego, California on 30 July-2 August 2001

Electron plasma columns continuously injected into a Malmberg-Penning trap display a rich evolution. Electrons emitted from an illuminated photocathode are trapped in the electrostatic well formed by the negatively biased photocathode and the trap end cylinder. Initially, the injections form cylinders of uniform density. As the density increases, the columns hollow in an attempt to match the potential profile of the equipotential cathode. The hollow columns are subject to the diocotron instability, and as the evolution becomes increasingly turbulent, the columns slowly expand to the trap wall. We present preliminary results and analysis of the trapping mechanism and the 2D dynamics of a continuously injected system., This article is from CP606, Non-Neutral Plasma Physics IV, p453-458, 2001. Pub. in AIP Conference Proceedings: volume 606. Prepared in cooperation with Ernst-Moritz-Arndt-Universitaet, Greifswald, Germany. This article is from ADA404831 Non-Neutral Plasma Physics 4. Workshop on Non-Neutral Plasmas (2001) Held in San Diego, California on 30 July-2 August 2001

The merging of an intense localized vortex with an extended vortex is investigated by means of an experimental analysis performed on a Malmberg-Penning trap with photocathode, and numerical simulations with a two-dimensional (2D) particle in cell (PIC) code. The study is restricted to highly nonlinear conditions, where the perturbative approach does not hold. A very good agreement between experimental results and simulations is obtained. It is found that the localized vortex is firstly wrapped around by the extended vortex, then moves towards the center of the system, eventually approaching an almost stationary state of rotation characterized by the formation of vorticity holes. During the whole evolution the extended vortex gains energy from the field surrounding the vortices, while the energy of the localized vortex remains constant., This article is from CP606, Non-Neutral Plasma Physics IV, p459-463, 2001. Pub. in AIP Conference Proceedings: volume 606. Prepared in cooperation with Ernst-Moritz-Arndt-Universitaet, Greifswald, Germany; I.N.F.M. (U.d.R. Milano Universita) and Dipartimento di Fisica, Universita degli Studi di Milano, Italy. This article is from ADA404831 Non-Neutral Plasma Physics 4. Workshop on Non-Neutral Plasmas (2001) Held in San Diego, California on 30 July-2 August 2001

We use electrostatic force microscopy and scanned gate microscopy to probe the conducting properties of carbon nanotubes at room temperature. Multiwalled carbon nanotubes are shown to be diffusive conductors, while metallic single-walled carbon nanotubes are ballistic conductors over micron lengths. Semiconducting single-walled carbon nanotubes are shown to have a series of large barriers to conduction along their length. These measurements are also used to probe the contact resistance and locate breaks in carbon nanotube circuits., Published in the Journal of Physical Review Letters, v84 n26 p6082-6085, 26 June 2000. Supported in part by DOE.

The research has been directed toward understanding the physics of superfluid phase slippage. The central goal is to observe and quantify acoustic fields radiated from the phase slip microaperatures. The sound field contains information about the stochastic processes driving phase slippage. The velocity dependent energy barrier for these processes has been determined. Understanding the acoustic pulses associated with phase slips has led to a demonstration of a superfluid Helium rotation sensor.

A central problem in forecasting and controlling nonlinear processes is quantifying the trade-off between available computational resources, model complexity, and prediction error. A more subtle, but important issue that strongly affects success is the choice of representation, or model class. Should one use Fourier or wavelet transforms, neural networks, hidden Markov models, or fuzzy logic, as modeling frameworks? As a tool for answering the questions of representation dependence, brittleness, and resource requirements, we introduced hierarchical e-machine reconstruction. This led to a number of detailed analyses of intrinsic computational capability in low-dimensional and spatially-extended nonlinear dynamical systems. This Final Technical Report outlines our investigations of the computational mechanics of learning complex systems during the period beginning 1 April 1991 and ending 29 February 1996. This project was supported under AFOSR grant number 91-0293. The report reviews the activities, personnel, and research highlights and lists the published papers and those currently under review.

The nature of inhomogeneous broadening in rare earth systems plays an important role in the dynamical optical -properties of ions in crystals. For this reason much of the work on the nature of the inhomogeneous broadening in rare earth doped systems has concentrated on the investigation of ion-ion interactions such as spectral transfer and up conversion processes. Variations in homogeneous optical dephasing times across the inhomogeneous optical line have also been reported. These studies concentrate on the variations of collective effects of ion- ion interactions at different positions in the inhomogeneous optical line in relatively heavily doped rare earth systems. We report variations in optically detected NQR (ODNQR) linewidths and shifts of Pr3+ hyperfine transitions in the optical ground state as a function of position in the inhomogeneous optical line and for satellite transitions of the 1D2-3H4 transition in lightly doped (0.5 at.%) Pr3+:LaF3. A systematic increase in the broadening of the Pr hyperfine transitions is observed as the laser is tuned toward the wings of the inhomogeneous optical transition without a shift of the NQR center frequency. The principle contribution to the 200KHz (FWHM) inhomogeneous width of the Pr hyperfine levels is explained by magnetic dipole-dipole interactions between the Pr nuclei and the neighboring fluorine spins. This contribution remains constant across the Stark broadened optical transition. Thus we show the existence of an additional broadening mechanism.

Photon echo measurements made at 2 OK on the 3H4 - ID2 transition in pr3+:LaF3 show that magnetic dipolar couplings between the Pr and F nuclei account for the 56 kHz homogeneous linewidth of this transition. The homogeneous broadening arises from the enhanced 141 Pr nuclear moment (I=5/2) interacting with the local field fluctuations of the 19 F nuclear moments undergoing mutual spin flip transitions. Such resonant fluctuations should, in the absence of a fluorine spin diffusion barrier, produce a homogeneous linewidth of about 200 kHz which is, in fact, roughly what is observed for the inhomogeneous broadening of the Pr3+ hyperfine levels and is considerably broader than that obtained by the photon echo measurements. Shelby et al 2 proposed a simple model analogous to the spin diffusion barriers responsible for narrowing the homogeneous lines in certain electron paramagnetic resonance transitions. In such systems, the field produced by the electron magnetic dipole moment (orders of magnitude larger than the enhanced nuclear moment associated with the ground state of Pr3+ in LaF3) de-tunes the nearest neighbors from each other, prohibiting mutual spin flips among them. Thus, the Fields produced by the neighboring spins are static and their interaction with the paramagnetic ion contributes to the inhomogeneous linewidth and not to homogeneous broadening.

Ultrashort duration, high-energy laser pulses have been generated using a titanium-doped-sapphire oscillator and amplifier system. The pulses have an energy of 0.45 Joules with a duration of 95 femtoseconds, and 0.23 Joules with a duration of 60 femtoseconds. We have constructed a titanium-aluminum oxide based laser system which uses chirped pulse amplification (CPA) and multipass amplifiers. Pulses are produced with a peak power of 3 TW, an energy of 0.45 J and a duration of 95 fs. The oscillator is a mode-locked Ti:A12O3 laser pumped by an Argon(+) laser.

This note provides a brief summary of the use of Fourier-Fresnel imaging to neutral atom interferometry. In applications of neutral-atom interferometry not requiring the interferometer to have an open (multiply connected) topology, the use of this imaging has significant advantages, notably ease of alignment, significantly increased through-put flux, ability to work with very short wavelength (and/or high velocity atoms). The results are primarily interesting in that they span the boundary between trapezoidal moire fringes and sinusoidal wave-interference fringes. Their limited applicability, perhaps accounts for the relative obscurity of many of the results to typical curricula of modern-day optics. The emphasis in this note is thus to put existing results (along with some additions that are needed for clarity) in a form suitable for use by techniques available for neutral-atom interferometry.

The research program is to study the spatial wave-like character of freely propagating neutral-atom matter-waves (deBroglie waves). To do so, we are constructing and using a neutral-atom matter-wave interferometer. An atomic beam will be decelerated and cooled by conventional laser spontaneous cooling. It will be extracted from the laser cooling apparatus and fed through a series of micro-fabricated transmission gratings, which will serve as an interferometer, and thence to a detector.

This note provides a brief summary of vibration isolation techniques and their application to our neutral atom interferometry experiments. Naturally, the difficulty in achieving acceptable vibration isolation for any given experiment depends largely upon the noise background of the laboratory, the noise generated by the experimental apparatus itself, as well as the tolerable noise sensitivity of the experiment. Since neutral atom interferometers may be configured to act as ultra-sensitive inertial sensors, their vibrational noise sensitivity is inherently high. The initial experiments are to simply demonstrate neutral atom interference. For these experiments any deviations from an inertial reference frame for the apparatus represent a potential noise source. Even the quasi-constant earth's gravitational field and rotation can be considered as very low frequency noise components, although subsequent experiments will consider these as known test signal's to be measured.

This contract terminates nearly ten years of Navy support for the invention and development of superconducting quasiparticle heterodyne receivers for millimeter wavelength radiation. Quantum effects such as mixer conversion gain and noise comparable to the limit set by the Heisenberg uncertainty principle have been experimentally observed. Mixer response at 36 and 90 GHz has been studied as a function of parameters such as RF and IF embedding impedance, local oscillator power, bias voltage, junction I-V curve, and operating temperature. Comparisons have been made with SIS mixer theory and good agreement has generally been found. These mixers are being used full time in heterodyne receiver systems at several radio astronomical observatories. They are the lowest noise millimeter wave receivers available today.

The goal of this research is to produce quantum limited SIS quasiparticle heterodyne receivers at submillimeter wavelengths. The approach used is to build prototype matching structures for 90 GHz and test them thoroughly. These matching structures will then be scaled to smaller dimensions to investigate their performance at submillimeter wavelengths. Substantial progress has been made toward these goals during the first grant year.

This contract has been directed at the examination of the bandwidth and sensitivity of semiconducting heterodyne detectors for far infrared radiation (FIR). Germanium detectors variously doped with gallium have been of prime interest. However, HeCdTe detectors have also been tested. While efforts to find good FIR heterodyne detectors have been slow, towards the end of the contract period substantial success was achieved and measurements have continued even past the contract period to round out what we regard as important quantitative measurements of improved detection. We have measured faster more responsive detectors and have reduced our system temperature. We have also seen for the first time, a change in detector bandwidth with bias voltage. We believe we have proceeded in the correct direction in detector fabrication and doping levels to produce faster detectors while retaining high responsivity.

The purpose of this project was to test whether the relative positions of stars could be measured with an infrared spatial interferometer to high accuracy--that is, 0.1 seconds of arc or better. For such a test, a number of measurements were made on the relative hour angles of three stars, omicron Ceti, alpha Orionis, and R Leonis, each separated by about 50 deg. About ten measurements of omicron Ceti and alpha Ori were made each night for 10 nights during a two-week period. The RMS deviation between measurements on a single night was approximately .07 arc seconds and the RMS variation from night to night among the 10 different nights was 0.08 arc seconds. Similar but less extensive results were obtained on R Leonis. This night-to-night positional accuracy is somewhat better than is normally achieved with the best optical techniques, and clearly of value for the Navy's task of assembling accurate stellar positions. The errors encountered appear to be largely due to mechanical instability of the telescopes used. These telescopes were not designed for astrometry, and had both bearing variations and temperature distortions which are estimated to be comparable with the errors found. Errors due to atmospheric seeing appeared to be substantially smaller than these. We believe this series of tests successfully achieved its objective and demonstrated the usefulness of infrared spatial interferometry for very precise astrometric measurements over large angular separations. (Author)

Quasiparticle mixers have shown strong quantum effects, conversion gain, and noise levels approaching the quantum limit, but only in tunnel junctions with very low sub-gap 'leakage' conductance. It has been suggested that SIS' tunnel junctions, made from two different coductors with unequal gaps, will function as high gain mixers since the dynamic conductance below the gap is nagative., Presented at the Applied Superconductivity Conference (1982). Prepared in cooperation with National Bureau of Standards, Boulder, CO. and Yale Univ., New Haven, CT.

We have measured the properties of a superconductor-insulator-superconductor (SIS) quasiparticle mixer which is operated in the quantum limit. Single sideband conversion gain larger than +4 dB was observed at 36 GHz with a mixer noise temperature T=9 + or - 6K, which is to be compared with the (Planck) quantum limit h-bar omega/(kln2) approx. 2.5K. Complete 3-port mixer calculations are presented which are in good agreement with the gain measurements. Negative resistance was observed which implies that arbitrarily large gain is available., Prepared in cooperation with Yale Univ., New Haven, CT. Dept. of Engineering and Applied Science.

The physical mechanisms which give rise to conversion gain in SIS quasiparticle mixers are studied. It is shown that the S-shape tunneling structure at the gap voltage of the I-V curve is essential in achieving conversion gain. In the development of SIS quasiparticle mixers, a new approach is used to analyse the embedding network of the mixing experiment. This method as described in this paper has the advantage over conventional methods that no separate measurements are necessary. In order to obtain a complete picture of the performance of SIS quasiparticle mixers, the photon-assisted tunneling theory used by Tucker to describe quasiparticle mixing is extended here to include pair current contribution. Based on this complete quantum theory the effects of the Josephson noise on SIS quasiparticle mixing is discussed and an upper frequency limit of SIS quasiparticle mixing is estimated. (Author)

Single particle (quasiparticle) tunneling through an insulating barrier between two superconductors or between a superconductor and a normal conductor is being used to make very low noise detectors and mixers for millimeter wavelengths. The nonlinearity of the I-V curve obtained from tunneling between two superconductors can be so strong that classical theory breaks down and photon assisted tunneling theory must be used to understand device performance. Quantum theory predicts that a quasiparticle tunnel junction can be operated as a microwave photon detector with quantum efficiency close to unity or as a heterodyne mixer with conversion gain and with mixer noise temperature comparable with the quantum noise limit T sub M = h omega/k. Both of these predictions have been experimentally realized at 36GHz using superconductor-insulator-superconductor junctions. It appears probable that these quasiparticle detectors and mixers will supersede the corresponding Josephson effect devices at millimeter wavelengths. (Author)

The strong nonlinearity of the quasiparticle tunneling current in superconductor-insulator-superconductor junctions near the full gap voltage 2 Delta/e can be used for direct detection of microwave signals. Measurements at 36 GHz yielded a current responsivity of 3,5000 A/W, which is within a factor of 2 of the quantum limited value e/h-bar omega. The measured NEP of 2.6 + or - 0.8 x 10 to the -16th power W/sq-rt. Hz is the lowest value reported to date and can probably be improved significantly. The experimental results are compared with both the standard classical analysis and photon assisted tunneling theory. (Author)

A comparison is made between several different methods for calculating energy transport within a wave field. Two Langevin techniques are developed. The first is based on the fluctuation dissipation theorem and provides relaxation rates nu(F)and a transport equation. The second method is an application of the Krylov-Bogoliubov-Mitropolsky perturbation theory and provides a Langevin rate constant nu(P) at lowest order. The two formulations are shown to be closely related to the radiative transfer (Boltzmann) equation whose rate is the difference between nu(F) and nu(P). Specific application of the Langevin methods is to internal waves in the ocean. Computations show that the GM-76 spectrum is approximately an equilibrium spectrum except for frequencies near the inertial frequency and at the lowest vertical mode numbers. The sensitivity of nu(F) and nu(P) to spectral form is also discussed. Simple analytic expressions for the rates are derived for the induced diffusion, elastic scattering, and parametric subharmonic instability mechanisms. Only the first of these mechanisms is ever of much numerical significance. Finally, net energy flow in the non-equilibrium portion of the GM-76 spectrum is discussed.

See also report dated 1975, AD-A056 301.