Atomic, Molecular, and Optical Physics (1986) / Chapter Skim
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1 A Program of Research Initiatives
1 A Program of Research Initiatives
Pages 7-28
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. THE NATURE OF THE FIELD The central goals of atomic, molecular, and optical physics (AMO physics)
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The interplay between various streams of research within AMO physics and neighboring fields of science is demonstrated frequently throughout this volume: an experiment on the quantum electrodynamics of electrons and positrons spurs a new technique for making atomic clocks and optical frequency standards; a close connection is discovered between inner-shell processes in energetic atomic collisions and in elementary chemical reactions; laboratory experiments with low-energy ions cause a rethinking of a basic astrophysical process. The unity of science is manifest throughout the field of AMO physics.
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In preparing the Program of Research Initiatives we are aware that attempts to predict the most promising avenues of scientific advances are likely to miss the most important developments. For instance, if we had met 10 years ago we would have failed to mention, or would have seriously underestimated, many areas of major progress in the past decade: laser cooling of atoms and ions, low-energy highly charged ions, transient molecular states, Rydberg atoms, molecular clusters, four-wave mixing, phase conjugation, and ultrasensitive detection, for example.
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· Transient States of Atomic Systems to describe qualitatively and quantitatively the physical nature of intermediate, nonstationary states; the exchange of energy, angular momentum, and particles during atomic collisions; and to understand the role of highly correlated intermediate states. Fundamental Tests and High-Precision Techniques The styles of physics the theoretical and experimental techniques of the various fields of physics differ dramatically, but central to all of physics is the study of the elementary laws of nature.
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invariance with a precision of 1 part in 10~3. There are new opportunities to search for the breakdown of time-reversal symmetry with a hundredfold increase in the sensitivity of the search for the neutron's electric dipole moment, to study particle-antiparticle symmetries, and to study electroweak interactions in atoms.
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c) Parity Violations in Atomic Physics.
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Very slow neutrons from a neutron reactor are trapped in a cell by a valve, and their intrinsic magnetic moment is measured by the technique of radio-frequency magnetic resonance. A strong electric field is applied; an electric dipole moment would reveal itself by a change in the resonance frequency when the electric field is reversed.
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Doubly excited states have been discovered in two-electron multiphoton ionization experiments. Using multiple-laser techniques it is possible to create "planetary" atoms atoms with two very highly excited electrons that can display new types of electronic motion.
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Recent developments of high-intensity synchrotron light sources, hard ultraviolet lasers, and charged-particle beams open the way to major advances in this area. · Spectroscopy of Highly Charged Ions Studies of sequences of ions having the same number of electrons but ever-increasing nuclear charge provide a unique opportunity to investigate the dependence of relativistic and QED effects on nuclear charge.
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Study of the transient electronic states that occur during violent collisions between ions and other ions or atoms has led to the discovery of approximate conservation laws, such as the electron promotion model that was created to explain the unexpected x-ray emission during ion-atom collisions. Other approximate conservation laws govern the evolution of highly excited atoms in electric fields, and a wide range of other atomic-physics phenomena.
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The experiments can reveal the dynamics of electron pickup and loss in individual quantum states and open the way to the study of energy transfer under controlled conditions. · Collisions in Laser Light As tunable lasers are developed over a wider spectral range, and femtosecond pulse techniques become widely available, new opportunities will be created for probing the elementary encounter event in a collision, a process heretofore inaccessible.
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By using new laser- and molecular-beam methods, one can observe collisions on a quantum state-to-state basis, including the coupling between electric and nuclear motion and the evolution of energy during collisions involving atoms and molecules. The Physics of Isolated Molecules Laser methods, synchrotron light sources, modern molecular-beam techniques, and other experimental advances provide the opportunity for a major advance in basic molecular physics and in the host of disciplines that hinge on molecular behavior.
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The study of unusual molecular species, for instance molecular ions, van der Waals and Rydberg molecules, metal cluster molecules and metastable species present new opportunities for understanding molecular structure. One can hope to understand how the electronic properties of molecules evolve into those of bulk material as one progresses from isolated atoms, through dimers and trimers, and to high states of aggregation; to understand what determines the geometric structure of a molecule whose constituents are held together by the weak van der Waals bond, and how the geometry of van der Waals molecules relates to crystal structure; to understand how the level structure of molecular Rydberg states resects the interactions within the molecular ion core.
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Further discussion can be found in Chapter 5 in the sections on The New Spectroscopy and Molecular Photoionization and ElectronMolecule Scattering. Research opportunities include the following: · Transient Molecular Species Short-lived highly reactive species, including ions, free radicals, and metastable molecules, can now be produced in supersonic beams and studied in detail.
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Moreover, it is now possible to produce molecular beams of a wide variety of unusual molecules including highly vibrationally excited molecules and molecular ions, radicals, and van der Waals moleculesfor use in novel collision studies. Modern lasers can dissociate molecules so as to create a "half-collision'' in which dynamical interactions occur only during separation of the products.
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By causing two such beams to cross, the collision dynamics of the two species can now be studied. INITIATIVE IN OPTICAL PHYSICS The invention of new lasers and other novel light sources, the development of new methods of spectroscopy and nonlinear optics, and the continued discovery of scientific and practical applications for these new technologies have combined to promote optics and optical physics to a forefront area of contemporary physics.
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Nonlinear optics, which has been a major arena for scientific and technical advances in optical physics, is not identified in a separate initiative area since it plays a role in nearly every one of the optics initiatives, as well as in the atomic and molecular initiatives. New Light Sources During the last decade a host of new light sources has become available for research and for industrial applications and for use in national programs: semiconductor diode lasers whose applications range from high-resolution infrared spectroscopy to fiber-optic communication; the tunable dye laser, which has revolutionized spectroscopy by providing a thousandfold increase in resolution and by opening the way to the preparation and study of atoms, ions, and molecules in states never before achieved; excimer lasers for applications in photochemical processing; the free-electron laser, which holds the promise of providing intense coherent radiation from the infrared through the ultraviolet regions; neodymium/glass lasers that are powerful enough to ignite thermonuclear fusion reactions; and laser-based ultraviolet and x-ray sources.
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Surface science, chemistry, biology, materials processing, and holography are a few of the many scientific and technical applications that await the development of intense sources of coherent light in the extreme-ultraviolet and soft x-ray regions of the spectrum. The upper left drawing shows a recently developed method for generating extreme-ultraviolet light by harmonic generation of near-ultraviolet laser light in a pulsed supersonic jet of helium.
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From page 26... ...
Such sources are complementary to synchrotron light sources, providing extremely bright light in certain spectral regions with relatively small-scale equipment. New methods for image formation and optical processing based on phase conjugation and other nonlinear processes can have important applications in optical communication, in astronomy, and in the manufacture of integrated circuits.
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From page 27... ...
These include highly stabilized tunable lasers, methods for trapping ions and atoms, laser cooling of atomic beams and trapped particles, coherent spectroscopic techniques, and optical-frequency-counting methods. In addition to the application to high-precision spectroscopy, including the study of slow dynamical processes in molecules, these advances create opportunities for new types of optical-frequency standards and atomic clocks, with applications in high-precision measurements and optical communications.
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· Electrodynamics at Long Wavelengths New types of radiative processes can be seen at microwave or millimeter-wave frequencies using highly excited atoms. The evolution from irreversible to reversible motion can be observed, and the basic source of noise in naturespontaneous emission can be modified.
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