Atomic, Molecular, and Optical Science An Investment in the Future (1994) / Chapter Skim
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2 Recent Major Advances and Opportunities in AMO Science and Applications to the Needs of Society
2 Recent Major Advances and Opportunities in AMO Science and Applications to the Needs of Society
Pages 36-107
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From page 36... ...
AMO science has enabled major technological advances in manufacturing, materials, communications, space, defense, energy, the environment, health, and transportation that have had a major impact on the nation's economic productivity, competitive position, security, and technological infrastructure and on the general well-being of its people. This chapter provides examples that highlight recent advances in AMO science and its applications and that illustrate the promise of the field.
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From page 37... ...
In suitably chosen systems, such precision measurements can probe physics far beyond the confines of what is customarily considered AMO science. For example, precision AMO measurements are testing our basic concepts of space and time, revealing new details about nuclear structure, probing the existence and properties of elementary particles, and exploring our fundamental understanding of the forces of nature.
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From page 38... ...
The study of the neutral weak force remains one of the best methods of testing the standard model of electroweak unification and probing the many unexplained features of this model. By themselves, the experimental atomic PNC data are not sufficient to probe the nature of the neutral weak force.
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From page 39... ...
Work is now under way to incorporate laser cooling techniques into these searches, which promises to lead to dramatic improvements. Efforts to improve special relativity tests and atomic PNC experiments have led to developments in laser stabilization and optics that are now spreading throughout the field of AMO science and, in particular, have had a substantial impact on techniques for laser cooling and trapping of atoms.
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From page 40... ...
This laser action occurs because in a micro-optical cavity, where one dimension is of the order of half a wavelength long, photons are emitted into a single mode, without spontaneous emission into all nonlasing modes, as in a conventional laser. Increased pumping then results in a gradual transition from predominantly spontaneous to predominantly stimulated emission, without a sharp threshold.
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From page 41... ...
Highly Perturbed Atoms in Intense Laser and Microwave Fields The interaction between laser light and atoms has been an active area of experimental and theoretical research since the discovery of the laser. By the early 1980s, these interactions were thought to be reasonably well understood, based on well-characterized perturbation theory.
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From page 42... ...
The universality of the ideas of chaos and nonlinear dynamics links these studies to recent investigations of such seemingly unrelated areas of atomic physics as the spectrum of the diamagnetic hydrogen atom, the doubly excited spectrum of the helium atom, Rydberg charge transfer, and the motion of charged particles in traps. These well-characterized and controlled studies in atomic physics can then serve as paradigms for higher-dimensional problems in other areas, including atomic or molecular collisions that are not weak and cannot be considered slow or fast, driven quantum wells, and other mesoscopic solid-state systems.
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From page 43... ...
Collisions at Ultralow Temperatures. Recent advances in laser cooling and manipulation of alkali, alkaline earth, and rare-gas metastable atoms have opened up many new opportunities in atomic collision studies.
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The enhanced long-range Coulomb forces between highly charged ions and other charged particles give rise to large cross sections for some processes. The electronic potential energy carried by the ion can overshadow kinetic effects in slow collisions.
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From page 46... ...
In some of the first experiments, the energy flow out of surface-adsorbed molecules has been observed directly. These approaches provide new details about charge transfer in molecules adsorbed on electrode surfaces, and nonlinear spectroscopy using the high fields created by ultrashort pulse lasers permits entirely new measurements that reveal the nature of molecules adsorbed on surfaces.
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From page 47... ...
The machinery for these fundamental studies is becoming sophisticated enough to allow modeling of practical systems, some of which urgently require a thorough understanding. Better state and time resolution will incisively test theoretical models and validate their application to ever more complex systems, many with important practical applications and impact.
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From page 48... ...
One nonlinear phenomenon of great interest is the soliton, a wave that propagates without distortion. Soliton pulses ranging from several hundreds of femtoseconds to a few picoseconds have been generated in optical fibers.
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From page 49... ...
Nonlinear optical processes have also been employed to produce states of light that display distinctly quantum mechanical properties. In the quantum theory of a mode of the electromagnetic field, two in-quadrature components are defined that play the role of canonical variables.
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From page 50... ...
The same basic concepts of nonlinear dynamics are found in work on atoms and molecules in electric and magnetic fields and in the dynamics of lasers and nonlinear optical interactions. Laser Cooling and Trapping Laser cooling is a technique for transferring momentum, and therefore kinetic energy, from an atom or atomic ion to the photons of a laser beam, as described in Chapter 1.
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From page 51... ...
It may also be possible to create a weakly interacting degenerate Fermi gas by laser cooling atoms with half-integral spin, which obey Fermi-Dirac statistics. Laser cooling techniques are being used in conjunction with "particle optics," as discussed in Chapter 1, to produce atomic beams of unprecedented intensity.
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From page 52... ...
Although many attempts had been made to achieve the required conditions, it was not until laser cooling was brought to bear on the problem that success was achieved (Figure 2.3~. Stable "solid" structures were observed with between 2 and approximately 30 ions.
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From page 53... ...
Questions concerning the nature of molecular adsorption and the dynamics of particle-surface interactions remain to be answered. Studies of particle-surface interactions have resulted in the observation of new atomic species, including so-called "hollow atoms." These are formed by resonant neutralization of slow, highly charged ions incident at grazing angles on a metal surface and comprise essentially neutral atoms having most of their electrons in high-lying Rydberg levels.
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From page 54... ...
Experimental techniques and measurement procedures that derive from AMO studies are widely used in other areas of science, including astrophysics, space science, atmospheric and environmental science, plasma physics, exotic atoms and nucle
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From page 55... ...
Providing these data is a major challenge. Experimental laboratory studies are essential for high precision and to test theoretical procedures, but the huge and growing volume of data that are needed can be provided only by theoretical calculations.
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From page 56... ...
Maximizing the sodium fluorescence requires a detailed understanding of the dynamics of the atomic interaction with the laser radiation (Figure 2.4~. Hyperfine splitting, Doppler broadening, coherent excitation, saturation, optical pumping, and radiation pressure are all important.
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From page 57... ...
Greatly improved data on X-ray spectra are expected to flow from spacecraft launched in the next several years. Except in a few cases, the collision cross sections, recombination rate coefficients, and radiative transition probabilities are currently available only as estimates of limited reliability.
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From page 58... ...
AMO science provides the atomic and molecular energy levels, optical transition probabilities, cross sections, and rate coefficients that are the central parameters in quantitative models. A recent example of the important role of AMO science in space is the discovery of the molecular ion H3+ and the explanation of unidentified lines in the Jovian aurora.
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From page 59... ...
This includes measuring quantities such as rate constants, cross sections, line shapes, scattering and extinction albe
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From page 60... ...
Theoretical molecular structure and molecular dynamics studies can often yield valuable information, particularly for species and/or physical conditions that pose experimental difficulties. The third research front is the development of sensitive physical and chemical sensors and their use in field measurements to quantify the current state of critical environmental parameters such as trace species concentrations, temperatures, and phase distributions.
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From page 61... ...
Atmospheric modeling and the interpretation of atmospheric diagnostics require accurate knowledge of molecular and atomic energy levels, transition probabilities, photodissociation and photoionization cross sections, reaction rates, and collision cross sections. The available data are incomplete, especially as concerns infrared and ultraviolet transitions in trace molecules and free radicals and reaction rates involving free radicals.
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From page 62... ...
The quest for inertial and magnetic confinement thermonuclear fusion demands an extensive database describing atomic phenomena in high-temperature plasmas in which intense electromagnetic fields and shock waves may be present. Conventional energy production devices, such as magnetohydrodynamic generators, have spurred extensions of our understanding of complex atomic interactions in external electromagnetic fields.
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From page 63... ...
In dense plasmas, the simple picture of atoms in a plasma breaks down, and methods similar to those developed in condensed matter physics and the physics of liquids must be invoked. Numerous opportunities and challenges for AMO science can be identified in plasma physics.
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From page 64... ...
and presents a method to achieve nuclear fusion without the high-temperature and confinement difficulties inherent in plasma fusion concepts. However, although a yield of ~150 fusions per muon has been experimentally observed in deuterium-tritium mixtures, this is still well short of that required for energy production.
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From page 65... ...
It may even prove possible to catalyze antihydrogen production via reactions of the metastable atoms with positrons or positronium. Surface and Condensed Matter Physics A rapidly expanding arsenal of analytical methods based on particle-surface interactions has been developed for use in surface and materials characterization.
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From page 66... ...
The advent of ultrashort pulse lasers and time-resolved optical measurement methods has contributed substantially to condensed matter physics and has enabled the direct study of dynamical phenomena in solids and at surfaces on time scales typical of the phenomena themselves. Accordingly, much new information has been obtained, primarily in the areas of surface dynamics, nonequilibrium heating of metals, carrier dynamics in semiconductors, and relaxation phenomena in amorphous materials.
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From page 67... ...
To that end, the lifetimes of image states at metal surfaces have been measured directly, and the extremely short lifetimes observed point to the importance of electronic deexcitation mechanisms in, for example, chemical processes occurring at surfaces. The nonequilibrium electronic properties of bulb solids is an active research area.
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From page 68... ...
The light forces associated with a focused laser beam are sufficient to hold and move individual microspheres and allow manipulation of individual DNA strands. In another optical approach to the Human Genome Project, genome sequencing using direct imaging X-ray color holography is being explored.
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From page 69... ...
Only the kilogram remains artifact-based and hierarchically disseminated. Even in the case of mass, however, AMO scientists are taking promising steps toward a possible atomic standard and replacement of this last vestige of artifact-based measurement.
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From page 70... ...
· High-resolution optical spectroscopy based on lasers, including Raman and other nonlinear optical spectroscopic techniques, with applications ranging
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From page 71... ...
AMO research and trained AMO scientists are essential in the invention of customized chemical analytical instruments such as the gas and liquid chromatographs, visible and infrared spectrometers, and mass spectrometers that are used in industry. The design and engineering of such instruments require a thorough training in molecular and optical science at all stages.
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From page 72... ...
industries maintain a competitive edge and successfully compete in world markets. Contributions of AMO science to industrial productivity include advances in lasers in manufacturing, plasma processing of materials, and chemical manufacturing.
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From page 73... ...
This minimizes thermal distortion in objects during cutting or welding operations and permits highly accurate micromachining (Figure 2.61. With an appropriate choice of wavelength, lasers can be used to process a wide FIGURE 2.6 Nd:YAG laser beam mills precise three-dimensional undamaged patterns in a lithium tantalate crystal.
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From page 74... ...
In recent years, there has been considerable interest in the etching and ablation properties of a variety of polymers and ceramics processed in air using excimer lasers. The mechanisms that give rise to polymer ablation are complex and wavelength sensitive, but research has advanced to the point that it is now possible to utilize the ablation process of manufacturing, specifically to pattern polymer films.
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The area has been reviewed recently and is discussed in a recent National Research Council (NRC) report, Plasma Processing of Materials: Scientific Opportunities and Technological Challenges (National Academy Press, Washington, D.C., 1991~.
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From page 76... ...
industries. (Reprinted from Plasma Processing of Materials: Scientific Opportunities and Technological Challenges, National Academy Press, Washington, D.C., 1991.)
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From page 77... ...
This, coupled with the recent availability of massive computational power, should advance the design of plasma reactors from an art to a science, further enhancing their effectiveness in manufacturing. Chemical Manufacturing Many AMO spectroscopic techniques, including atomic absorption spectroscopy, Fourier transform infrared spectroscopy, Raman spectrometry, and electron spin resonance spectrometry, are widely used in chemical manufacturing.
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From page 78... ...
The foundations for the physical aspects of these industries lie in the AMO sciences. AMO research on laser sources and optical detectors as well as optical pulse propagation in fibers has provided the basic knowledge base for optical communications and optical data storage.
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From page 79... ...
and simultaneous amplification of multi-optical-channel signals in a single fiber amplifier system. The fiber-optic amplifier has also been shown to be suitable for amplifying optical signals with various formats, including telephone, high-speed data, and television signals.
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From page 80... ...
There are a number of research opportunities in this area. For example, many optical communications systems operate with laser radiation having a wavelength of 1.3 ~m, which is not in the 1.5-pm operating regime of the erbium-doped fiber amplifier, and AMO research aimed at developing optical amplifiers in the 1.3-,um regime could have great impact on this installed base of systems.
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From page 81... ...
AMO science offers the potential for dramatic improvements in optical storage technology. Information storage densities can be improved by using shorter optical wavelengths in the optical recording and reading head because shorter wavelengths can be focused to a smaller spot size.
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From page 82... ...
Spectroscopic investigations provide the detailed knowledge of energy levels and intramolecular processes needed to begin to understand the
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From page 83... ...
RECENT MAJOR ADVANCES AND APPLICATIONS 83 FIGURE 2.9 Detailed diagnostics of various forms of combustion chambers are extremely important to interpret the combustion process in terms of atomic and molecular processes occurring in the chamber. Atomic and molecular data are then needed to properly model the process and point to ways to optimize combustion.
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From page 84... ...
The rapid increase in computational power suggests that now is the time to begin thinking seriously about what new molecular physics is required to support the development of these models. As an example, it will be necessary to know in detail the range of validity of statistical theories of chemical reaction rates, which entails understanding how quickly energy moves through molecules and whether the end result is random.
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From page 85... ...
These energy loss mechanisms require new knowledge of the spectroscopy and excitation-recombination cross sections of atomic ions and information about the effects of strong electromagnetic fields on atomic properties and processes. A valuable contribution of atomic theory to the design of magnetic fusion reactors has been the demonstration that the presence of small fractions of highly charged heavy ions can lead to significant energy loss.
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From page 86... ...
Studies of Thompson scattering of laser light and the photons emitted following electron capture by impurity ions from neutral hydrogen beams have been particularly valuable in this respect. Fusion: Inertial Confinement.
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From page 87... ...
In addition, the contributions of atomic physics to the understanding of interactions in plasmas of highly stripped atoms particularly for advanced targets employing complex mixtures of elements to control energy transport and hydrodynamics during the implosion are important not only for laser-driven targets, but also for heavyion drivers, which are viewed as attractive candidates for commercial energy production. Correlation of theoretical models with experimental data from existing laser target facilities, or from the next-generation laser driver proposed for reaching thermonuclear ignition, will be crucial to evaluating the feasibility of inertial confinement fusion for energy production as experiments push into regimes of higher plasma density than have been explored to date.
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From page 88... ...
There is increasing international concern about the impact on Earth of human activities, in particular in the areas of global warming, depletion of the ozone layer, and pollution problems such as acid rain (Figure 2.11~. As discussed in the section on atmospheric and environmental science, AMO science plays a pivotal role in the development of computer models to analyze the effects of changes in atmospheric composition and in the provision of reaction rates, collision cross sections, line shapes, and so on, for inclusion in such models.
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From page 89... ...
, microprocessor-based control electronics, and other technologies have recently spurred the development of highly sensitive, real-time spectroscopy-based measurement techniques for many key atmospheric trace species. FIGURE 2.11 The ozone hole is expanding in size, as indicated here, with attendant risks that plants, animals, and humans will be exposed to excessive amounts of ultraviolet light.
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From page 90... ...
, a form of remote laser spectroscopy, provides a graphic example of the use of AMO science in field measurements and is the oldest field application of laser spectroscopy in atmospheric remote sensing. In its simplest form, fluorescence LIDAR, a laser is tuned to a resonance excitation of the species of interest.
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From page 91... ...
In addition, atomic and molecular processes and spectroscopy play an important role in such areas as radio propagation in the ionosphere, atmospheric infrared transmission, infrared background emissions, radiation trapping in nuclear bursts, nuclear blackout of electromagnetic propagation, and missile plume detection and analysis.
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From page 92... ...
There have been few experimental measurements of the opacity, that is, the degree of absorption of transmitted light, for plasmas at moderate or high temperatures and density. The calculation of opacities requires a large atomic or molecular database, with information on the energy levels of several ionic stages of each species in the plasma and of the corresponding radiative transition probabilities and line shapes.
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From page 93... ...
, heat-seeking missiles, and infrared lasers. Data on atomic and molecular processes are vital to the understanding of atmospheric and meteorological phenomena that affect military scenarios.
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From page 94... ...
C3~ommunication, Command, and Control Fiber optics are being used increasingly in military communication, command, and control systems because of their high bandwidth, small size, freedom from noise and cross talk, ability to withstand electromagnetic impulses, and the security provided by their low radiant emission. They interconnect computer systems within command centers, within aircraft and within ships.
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From page 95... ...
The description of its evolution and its return to the undisturbed state depends on a complex variety of atomic and molecular processes involving ions, neutral atoms, and charged and neutral molecules in abnormal distributions of energy levels. With the atmospheric test ban ulna the mnr~torilim on ~'n~l~.rsrro~ln(1 testing lahoratorv simulations of the highly The increase in ~ ace_ I., ~^ am...
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From page 96... ...
Lasers have become indispensable tools in numerous therapeutic and diagnostic medical procedures. A laser beam can be precisely focused at discrete lesions in the eye, the skin, or other exposed areas and can also be directed through thin flexible optical fibers, allowing, in principle, laser treatment of any body organ through a minimally invasive procedure (Figure 2.121.
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From page 97... ...
Cancerous tumors are poorly supplied by blood vessels compared to normal tissues and cannot readily disperse heat. Thus, it is possible to locally heat and destroy a tumor using laser radiation introduced by an optical fiber.
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From page 98... ...
The laser radiation serves as a scalpel, cutting adhesions and endometrial tissue with minimum damage to surrounding healthy tissue. (Courtesy of Coherent, Inc., Palo Alto, Calif.)
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From page 99... ...
The acoustic shock waves that result from pulsed-laser ablation are used to clinical advantage in the treatment of kidney stones. Stones lodged in the urinary tract are often fragmented by shock waves when illuminated with visible pulsed dye laser light.
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From page 100... ...
(These spectroscopic techniques can also be used to monitor heavy metals and other species present in the blood.) Studies using isotopic tracers require the availability of large amounts of isotonically enriched material, but these can be obtained by using laser isotope separation.
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From page 101... ...
Analyzing the subsequent chain of events and their possible effects requires a detailed spectroscopic knowledge of the pertinent excited and ionized states and the cross sections for all the major collision processes operative, remembering that the predominant chemical reactions in ground and excited-state collisions may be different. Further research is required to establish a more complete database of cross sections for collisions of electrons, protons, and heavy ions with molecules, especially polyatomic molecules of biological importance such as water and the hydrocarbons.
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From page 102... ...
However, improved quantum mechanical methods for treating larger systems by semiempirical or ah initio techniques are required, together with development of improved parallel molecular dynamics algorithms to allow for more realistic simulations and for treatment of supramolecular systems such as biological mem branes. AMO science is important in a number of health-related areas, especially medicine.
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From page 103... ...
Research is under way to connect several microwave antennas with lasers by means of fiber-optic systems, but achieving this goal requires a detailed understanding of the noise properties of semiconductor lasers modulated by ultrastable microwave sources and the effects of fiber-optic transmission. Spacecraft Navigation and Communication Satellite-based laser communication links are being explored because they can be made very directional.
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From page 104... ...
For example, the cesium atomic clock is used on the Global Positioning System satellites. Recent developments in the field of atom-ion trapping and cooling suggest that with further research greatly improved spacecraft clocks can be developed that will offer much higher accuracies.
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From page 105... ...
High-sensitivity light scattering techniques developed by AMO researchers are being applied to the detection of wind shear. For instance, a LIDAR system can measure wind velocity through minute frequency shifts of laser light scattered from moving aerosol particles in the atmosphere.
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From page 106... ...
Inexpensive and localized laser radar systems may be used to assist in collision avoidance. Optical fiber sensors are being developed to monitor combustion within the cylinders of an automobile engine.
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From page 107... ...
RECENT MAJOR ADVANCES AND APPLICATIONS \ ,~ / \1~, \ ~ 107 FIGURE 2.14 The extremely accurate timing made possible by atomic clocks has made the Global Positioning System a reality. An affordable receiver gets timing signals from satellites, and a built-in computer triangulates from the satellite locations to give locations on (or above)
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