Matter-radiation Interactions Research Articles

Infinite Order Hydrodynamics: An Analytical Example.

We construct a kinetic model for matter-radiation interactions whose hydrodynamic gradient expansion can be computed analytically up to infinite order in derivatives, in the fully nonlinear regime, and for arbitrary flows. The frequency dependence of the opacity of matter is chosen to mimic the relaxation time of a self-interacting scalar field. In this way, the transient sector simulates that of a realistic quantum field theory. The gradient series is found to diverge for most flows, in agreement with previous findings. We identify, for the model at hand, the mechanism at the origin of the divergence, and we provide a successful regularization scheme. Additionally, we propose a universal qualitative framework for predicting the breakdown of the gradient expansion of an arbitrary microscopic system undergoing a given flow. This framework correctly recovers all previously known instances of gradient expansion divergence. As a new prediction, we show that the gradient expansion diverges when the energy-dependent mean free path is unbounded above.

Dynamical Coupling between Particle and Antiparticle in Relativistic Quantum Mechanics: A Multistate Perspective on the Energy–Momentum Relation

A molecular formalism based on a decomposed energy space constructed by a modular basis of matter and radiation is proposed for relativistic quantum mechanics. In the proposed formalism, matter radiation interactions are incorporated via the dynamical transformation of the coupled particle/antiparticle pair in a multistate quantum mechanical framework. This picture generalizes relativistic quantum mechanics at minimal cost, unlike quantum field theories, and the relativistic energy–momentum relation is interpreted as energy transformations among different modules through a multistate Schrödinger equation. The application of two-state and four-state systems using a time-dependent Schrödinger equation with pair states as a basis leads to well-defined solutions equivalent to those obtained from the Klein–Gordon equation and the Dirac equation. In addition, the particle–antiparticle relationship is well manifested through a particle conjugation group. This work provides new insights into the underlying molecular mechanism of relativistic dynamics and the rational design of new pathways for energy transformation.

Estimation of radioactive activity by gamma spectroscopy

Radioactive sources of isotopes 22Na, 137Cs, 60Co, 133Ba and decay chains of Th and U are analyzed by means of gamma spectroscopy. The instrument used, a cylindrical NaI(Tl) scintillator from Mirion Technologies (Canberra) with dimensions of 2 × 2, is characterized by its calibration and absolute efficiency. The peak energies of the gamma spectra obtained are identified and related to corresponding isotopes and matter-radiation interactions according to nuclear and atomic databases. From these data, spectroscopic methods are implemented to compute radioactive activities for each source.

X-ray Free Electron Laser Accelerator Lattice Design Using Laser-Assisted Bunch Compression

We report the start-to-end modeling of our accelerator lattice design employing a laser-assisted bunch compression (LABC) scheme in an X-ray free electron laser (XFEL), using the proposed Matter-Radiation Interactions in Extremes (MaRIE) XFEL parameters. The accelerator lattice utilized a two-stage bunch compression scheme, with the first bunch compressor performing a conventional bulk compression enhancing the beam current from 20 A to 500 A, at 750 MeV. The second bunch compression was achieved by modulating the beam immediately downstream of the first bunch compressor by a laser with 1-μm wavelength in a laser modulator, accelerating the beam to the final energy of 12 GeV, and compressing the individual 1-μm periods of the modulated beam into a sequence of microbunches with 3-kA current spikes by the second bunch compressor. The LABC architecture presented had been developed based on the scheme of enhanced self-amplified spontaneous emission (ESASE), but operated in a disparate regime of parameters. Enabled by the novel technology of the cryogenic normal conducting radiofrequency photoinjector, we investigated an electron beam with ultra-low emittance at the starting point of the lattice design. Our work aimed at mitigating the well-known beam instabilities to preserve the beam emittance and suppress the energy spread growth.

High-Brightness Beam Technology Development for a Future Dynamic Mesoscale Materials Science Capability

A future capability in dynamic mesoscale materials science is needed to study the limitations of materials under irreversible and extreme conditions, where these limitations are caused by nonuniformities and defects in the mesoscale. This capability gap could potentially be closed with an X-ray free-electron laser (XFEL), producing 5 × 1010 photons with an energy of 42 keV, known as the Matter–Radiation Interactions in Extremes (MaRIE) XFEL. Over the last few years, researchers at the Los Alamos National Laboratory have developed a preconceptual design for a MaRIE-class XFEL based on existing high-brightness beam technologies, including superconducting L-band cryomodules. However, the performance of a MaRIE-class XFEL can be improved and the risk of its operation reduced by investing in emerging high-brightness beam technologies, such as the development of high-gradient normal conducting radio frequency (RF) structures. Additionally, an alternative XFEL architecture, which generates a series of high-current microbunches instead of a single bunch with uniformly high current along it, may suppress the most important emittance degradation effects in the accelerator and in the XFEL undulator. In this paper, we describe the needed dynamic mesoscale materials science capability, a MaRIE-class XFEL, and the proposed microbunched XFEL accelerator architecture in detail.

Magnetizing the Cosmic Web during Reionization

Increasing evidence suggests that cosmological sheets, filaments, and voids may be substantially magnetized today. The origin of magnetic fields in the intergalactic medium (IGM) is, however, currently uncertain. It seems well known that non-standard extensions to the physics of the standard model can provide mechanisms susceptible of magnetizing the universe at large. Perhaps less well known is the fact that standard, classical physics of matter–radiation interactions actually possesses the same potential. We discuss a magnetogenesis mechanism based on the exchange of momentum between hard photons and electrons in an inhomogeneous IGM. Operating in the neighborhood of ionizing sources during the epoch of reionization, this mechanism is capable of generating magnetic seeds of relevant strengths over scales comparable to the distance between ionizing sources. In addition, summing up the contributions of all ionizing sources and taking into account the distribution of gas inhomogeneities, we show that this mechanism leaves the IGM, at the end of reionization, with a level of magnetization that might account, when amplification mechanisms take over, for the magnetic fields strengths in the current cosmic web.

Dark matter–radiation interactions: the impact on dark matter haloes

Interactions between dark matter (DM) and radiation (photons or neutrinos) in the early Universe suppress density fluctuations on small mass scales. Here we perform a thorough analysis of structure formation in the fully non-linear regime using N-body simulations for models with DM-radiation interactions and compare the results to a traditional calculation in which DM only interacts gravitationally. Significant differences arise due to the presence of interactions, in terms of the number of low-mass DM haloes and their properties, such as their spin and density profile. These differences are clearly seen even for haloes more massive than the scale on which density fluctuations are suppressed. We also show that semi-analytical descriptions of the matter distribution in the non-linear regime fail to reproduce our numerical results, emphasizing the challenge of predicting structure formation in models with physics beyond collisionless DM.

Journal of Dynamic Behavior of Materials: A New Forum for Knowledge Exchange on Dynamic Material Response, High Strain-Rate Effects, Shock, and Materials Under Extreme Loading

We are excited to introduce the Journal of Dynamic Behavior of Materials (JDBM) as the new journal of the Society for Experimental Mechanics (SEM). We wish to invite you to submit your best work on the study of the dynamic behavior of materials to the journal and help in getting the word out to your colleagues. Information on the journal can be found at http://springer.com/40870. The field of dynamic behavior of materials is undergoing a revolution with increasing interdisciplinary focus and unprecedented new level of diagnosis at the bench scale and numerous user facilities. Classic loading techniques including split Hopkinson pressure (Kolsky) bar, gas/ powder guns, and high-explosives are being pushed to increased levels of precision, linked with new and novel diagnostics enabling previously unattainable levels of in situ measurement combined with advanced high resolution and three-dimensional post-mortem observation. National User Facilities are enhancing their capacities for studying materials in extremes with new facilities being developed ranging from SLAC’s Linac Coherent Light Source, the Dynamic Compression Sector at the Advanced Photon Source at Argonne National Laboratory, the Z-Machine at Sandia National Laboratories, the National Ignition Facility at Lawrence Livermore National Laboratory, and Matter-Radiation Interactions in Extremes at Los Alamos National Laboratory. An exciting collaboration at GSI in Darmstadt is incorporating expertise from pRad and LANSCE at Los Alamos National Laboratory in the USA and the Institute for Theoretical and Experimental Physics in Russia using the PRIOR microscope with great potential for studying dynamic materials processes. The Diamond Light Source located at the Harwell Science and Innovation Campus in the UK has been offering great levels of postmortem investigation of damage from dynamic loading. Exciting capabilities exist at these and other facilities around the world to advance the state-of-the-art for studies of dynamic behavior of materials. Advances in modeling & simulation of dynamic loading and material response have paralleled these experimental advances. Continued evolution in computing hardware is enabling calculations with extraordinary fidelity in representation of highly coupled complex physics. Great advances have been made in density functional theory, molecular dynamics, and dislocation dynamics based material models. Simulations based on these theories have historically had to be performed at very high strain-rates and in very short time and length scales. Advances in these models and the hardware on which these simulations are performed have brought them into line with the regimes of many platforms for dynamic experiments. New theories and models of material behavior are being developed to take advantage of understanding material at the mesoscale. Continuum level constitutive models are being proposed and developed with greater levels of physical underpinning and predictive ability. The state-of-the art in modeling & simulation and experiments along with the interdisciplinary approach to modern science and engineering have lead to significant payoff from hybrid experimental-computational approaches. Advances in simulation are enabling the development and optimization of experiments, with better understanding of the underlying physics and data capture. Conversely, advances in experimentation are pushing better models, codes, and simulations. The JDBM offers a single source to bring this broad, vibrant international community together. This peer E. N. Brown (&) Los Alamos National Laboratory, Los Alamos, NM 87545, USA e-mail: en_brown@lanl.gov

The science of dynamic compression at the mesoscale and the Matter-Radiation Interactions in Extremes (MaRIE) project

A scientific transition is underway from traditional observation and validation of materials properties to a new paradigm where scientists and engineers design and create materials with tailored properties for specified functionality. Of particular interest are the regimes of materials' response to thermo-mechanical extremes including materials deforming under imposed strain rates above the quasi-static range (i.e. > 10−3 s−1), material subjected to imposed shocks, but also material response to static, high-pressures. There is a need for the study of materials at the "mesoscale," the scale at which sub-granular physical processes and inter-granular organization couple to determine microstructure, crucially impacting constitutive response at the engineering macroscale. For these reasons Los Alamos is proposing the MaRIE facility as a National User Facility to meet this need. In particular, three key science challenges will be identified: Link material microstructure to macroscopic behavior under dynamic deformation conditions; Make the transition from observation and validation to prediction and control of dynamic processes; and Develop the next generation of diagnostics, dynamic drivers, and predictive models to enable the necessary, transformative research.

Enhancing nanoparticle electrodynamics with gold nanoplate mirrors.

Mirrors and optical cavities can modify and enhance matter-radiation interactions. Here we report that chemically synthesized Au nanoplates can serve as micrometer-size mirrors that enhance electrodynamic interactions. Because of their plasmonic properties, the Au nanoplates enhance the brightness of scattered light from Ag nanoparticles near the nanoplate surface in dark-field microscopy. More importantly, enhanced optical trapping and optical binding of Ag nanoparticles are demonstrated in interferometric optical traps created from a single laser beam and its reflection from individual Au nanoplates. The enhancement of the interparticle force constant is ≈20-fold more than expected from the increased intensity due to standing wave interference. We show that the additional stability for optical binding arises from the restricted axial thermal motion of the nanoparticles that couples to and reduces the fluctuations in the lateral plane. This new mechanism greatly advances the photonic synthesis of ultrastable nanoparticle arrays and investigation of their properties.

Congratulations Larry!

It is with great pleasure that I compose this editorial in celebration of our Editor in Chief's 2013 Pittsburg Spectroscopy Award. If this Editorial goes to plan, this will be the only article in recent years not to have been vetted by our illustrious Editor in Chief, so Larry, I apologize for circumventing your solid Editorial system but…SURPRISE! The 2013 Pittsburg Spectroscopy Award is presented by the Spectroscopy Society of Pittsburgh and presented in honor of an individual who has made outstanding contributions in the field of spectroscopy. Since before I was born, a younger then ‘Dr.’ Nafie was shaking things up in the world of vibrational spectroscopy; his 1972 paper Reorientation and vibrational relaxation as line broadening factors in vibrational spectroscopy has received a remarkable 228 citations to date. Just one of the many classic articles from Larry's early career. Since these extraordinary beginnings, Larry has amassed a bibliography of 274 articles from 1969 to 2012 (as indexed by the Web of Science) having attracted an impressive 341 citations in 2011 alone. Plus, of course, there is his infamous book, Vibrational Optical Activity – Principles and Applications. Larry is perhaps the world's most foremost expert on vibrational circular dichroism (VCD) and Raman optical activity (ROA). He has pioneered the use of these spectroscopic techniques for addressing questions of structure and function for a wide range of biological or model biological molecular systems. Most recently, demonstrating their use, combined with state of the art computations, for investigations of protein structure function relationships. In part, Larry's recognized success and impact derives from his in-depth theoretical knowledge and understanding of matter–radiation interactions coupled with his experimental prowess in the clever design and implementation of instrumentation. In addition, he has identified important problems in biophysics where these novel spectroscopic methodologies can be applied. It is accurate to say that Larry has built both the theoretical as well as instrumental machinery that the current fields of VCD and ROA are built on. Larry's scientific impact has been further enhanced by his efforts to make state-of-the-art instrumentation required for these circularly polarized measurements commercially accessible for laboratories throughout the world via Biotools, Inc., the company he founded offering VCD and ROA instrumental platforms. This recognition by the Pittsburgh Conference is not the first award that recognizes his creative and significant scientific achievements. Larry's previous awards in recognition of his innovative contributions to the modern techniques and current applications of molecular spectroscopy including an Alfred P. Sloan Fellowship, the Coblentz Award, the Bomem Michelson Award, the Meggars Award, and he is a Fellow of the Society of Applied Spectroscopy. Thank you Larry and congratulations!

Analysis of the Spatial Distribution of Free Radicals in Ammonium Tartrate by Pulse EPR Techniques

Using pulse electron paramagnetic resonance (EPR) on a series of l(+)-ammonium tartrate (AT) dosimeters exposed to radiations with different linear energy transfer (LET), we assessed the ability of pulse EPR spectroscopy to discriminate the quality of various radiation beams such as (60)Co gamma-ray photons, protons and thermal neutrons at various doses by analyzing the local radical distributions produced by the different beams. We performed two types of pulse EPR investigations: two-pulse electron spin echo decay obtained by varying the microwave power, and a double electron-electron resonance (DEER) study. Both methods provide information about the dipolar interactions among the free radicals and about their spatial distributions. The first method provided information on the instantaneous diffusion and hence the microscopic concentration of the radicals that is compared with the macroscopic one obtained by CW-EPR. The DEER spectra yielded the distributions of distances between pairs of radicals two to five crystal cells apart produced by the same radiation event, a result reported here for the first time. The inter-radical distributions given by the DEER results have been simulated by modeling the radical distributions according to the details of the matter-radiation interactions for the various beams. The results of both types of pulse experiments are strongly dependent on the radiation quality. This was also observed for samples giving indistinguishable CW-EPR spectral profiles. We conclude that the pulse EPR measurements can be valuable tools for distinguishing the LET of the radiation beams, an important parameter for radiobiological considerations.

Review Article

We present a review of theoretical and experimental aspects of multiphoton quantum optics. Multiphoton processes occur and are important for many aspects of matter–radiation interactions that include the efficient ionization of atoms and molecules, and, more generally, atomic transition mechanisms; system-environment couplings and dissipative quantum dynamics; laser physics, optical parametric processes, and interferometry. A single review cannot account for all aspects of such an enormously vast subject. Here we choose to concentrate our attention on parametric processes in nonlinear media, with special emphasis on the engineering of nonclassical states of photons and atoms that are relevant for the conceptual investigations as well as for the practical applications of forefront aspects of modern quantum mechanics. We present a detailed analysis of the methods and techniques for the production of genuinely quantum multiphoton processes in nonlinear media, and the corresponding models of multiphoton effective interactions. We review existing proposals for the classification, engineering, and manipulation of nonclassical states, including Fock states, macroscopic superposition states, and multiphoton generalized coherent states. We introduce and discuss the structure of canonical multiphoton quantum optics and the associated one- and two-mode canonical multiphoton squeezed states. This framework provides a consistent multiphoton generalization of two-photon quantum optics and a consistent Hamiltonian description of multiphoton processes associated to higher-order nonlinearities. Finally, we discuss very recent advances that by combining linear and nonlinear optical devices allow to realize multiphoton entangled states of the electromagnetic field, either in discrete or in continuous variables, that are relevant for applications to efficient quantum computation, quantum teleportation, and related problems in quantum communication and information.

Nanophotonics: a new multidisciplinary frontier

Nanophotonics, defined as nanoscale optical science and technology, is a new multidisciplinary frontier. This article presents our studies on nanoscale matter–radiation interactions utilizing nanoscale confinement of radiation as well as on nanoscale photochemical transformations, particularly nanoscale nonlinear optical interactions. The selected examples of our studies include nanoscopic optical harmonic generation, multiphoton fluorescence, transient absorption dynamics, surface-plasmon-enhanced two-photon fluorescence, and nonlinear optical information storage.

Charge transfer in He++-He collisions at keV energies in an intense laser field: A theoretical close-coupled study using a diabatic molecular representation

We carry out a theoretical study of the effect of a strong laser field on charge transfer in collisions of doubly charged helium ions with helium at keV energies, using a close-coupled treatment with a diabatic molecular wave function basis in the semiclassical impact parameter approximation. Our results show significant effects of the laser intensity, wavelength and the orientation of the (linear) laser polarization on the charge transfer cross-sections. Our results also indicate the possibility of an experimental test for differentiating between the effects of the minimal coupling and the multipolar matter-radiation interactions on ion-atom collision processes.

What is the contribution of electrical field to the microwave sintering of YBCO

The possibility of heating and sintering a YBCO superconductor in a single-mode cavity has been discussed by various authors and is thought to be related to the interaction between the electrical field and matter. New results are presented here that show different behaviour of matter-radiation interactions for cylindrical samples aligned parallel to the electrical field in the microwave cavity. Only bars smaller than the width of the cavity can be heated in their central zone in spite of a uniform distribution of the electrical field around the sample. The limited heated zone and the discrepancy between the temperature of this zone versus the applied electrical field show that the law P=KEa2 does not describe the real heating process, suggesting that the electrical field is not the only factor that governs the heating of YBCO.

Fractional gauge transformations of the first kind: Optimization of cross-section calculations

A theory of matter-radiation interactions is presented that incorporates a fractional gauge transformation. The transformation is achieved with the Göppert-Mayer generator multiplied by a continuously variable gauge parameter. The derived Hamiltonian contains a mixture of A⋅p and E⋅x interaction terms: The field and matter variables within the full gauge-invariant, matter-radiation Hamiltonian are intermixed. Practical implications for calculating accurate transition cross sections using convenient, but inexact, matter eigenstates are developed by interpreting gauge-generalized perturbation theory as a gauge-variational theory. By minimizing the matter/field/interaction ground state energy with respect to gauge variations, the optimum matter-radiation basis for the chosen set of inexact matter states is obtained. The gauge optimization technique is demonstrated quantitatively for the 2pσu –1sσg electronic transition of H+2 using the simple LCAO-MO basis.

Accretion onto magnetic neutron stars: Radiative transport

Three different levels of approximation are considered in an attempt to simplify scattering terms in radiation transfer equations for the matter-radiation interactions of accretion by a neutron star. An Eddington approximation eliminates the directional dependency of the specific intensity and yields a set of moment equations for the spectral energy density and flux vector. An analytical approximation is also made for the photon frequency redistribution function. Second, a Fokker-Planck aproximation limit is used to describe the scattering process in the nonmagnetic case. Planck mean values for frequency averaged interaction coefficients can be used in a hydrodynamical description of the energy field. A mean coefficient for the total momentum exchange is derived which is consistent with the diffusion approximation and is therefore valid for an optically thick field. 13 references.

A generalized Franck–Condon principle for vibronic bands of diatomic molecules

The traditional Franck–Condon principle is limited in usefulness because empirical electronic transition matrix elements are not generally constant across a vibronic molecular transition band. Empirical generalizations that preserve the utility of the Franck–Condon overlap integral account for variations of the electronic matrix elements for diatomic bands in terms of transition frequency, as in a frequency-generalized Franck–Condon approximation [G. W. Robinson and R. A. Auerbach, J. Chem. Phys. 74, 2083 (1981)], or in terms of internuclear distance, as in the well-known r-centroid approximation. This paper illustrates empirically the validity of the Robinson–Auerbach method, and its relationship to the r-centroid approximation, for vibronic bands of some diatomic molecules. Most importantly, the former empirical method is derived from a gauge-invariant theory of matter-radiation interactions developed recently by Brown and Robinson [C. W. Brown and G. W. Robinson, J. Chem. Phys. (submitted)]. Both the empirical method and the gauge-invariant theory utilize continuous variability between dipole length and velocity matrix elements Rμν and Pμν/m, respectively. Using a gauge parameter ξ, the value of which is immaterial with exact molecular eigenstates, this variability is fixed in the empirical method by the ratio (im ωμνRμν/Pμν)ξ, which is unity with exact eigenstates, and in the theory by the difference ξ(im ωμνRμν−Pμν), which vanishes with exact eigenstates. The empirical form of the variability is obtained from the theory when the difference im ωμνRμν −Pμν small. The generalized Franck–Condon principle presented here has never before been successfully derived from theory.