Physics Commons^™

Differential, Partial Cross Sections For Electron Excitation Of The Sodium 3p State, Xianming Han, G. W. Schwinn, A. Gallagher

Xianming Han

Using a powerful laser-based experimental method, the cross section for electron excitation of Na(3S) atoms to the Na(3P) state has been decomposed into partial components with respect to changes in the spin and angular momentum of the atomic electron, and these partial cross sections are further reduced to their differential character with respect to the electron scattering angle. Partial, differential cross sections are reported for electron collision energies from threshold 2.1 to 3.6 eV, and compared to available calculations.

Superfluorescence Polarization: Signature Of Collisional Redistribution, A. Kumarakrishnan, S. Chudasama, Xianming Han

Xianming Han

We have studied effects of magnetic sublevel degeneracy on the polarization of superfluorescent pulses generated on the Ca 4s4p1P1–3d4s1D2 transition at 5.5μm. These pulses were generated from a cell of length 50 cm by optically pumping calcium vapor on the 4s21S0–4s4p1P1 transition in the presence of Ar gas. The axis of ellipticity of superfluorescence (SF) polarization is oriented parallel to the axis of the pump-laser polarization at large detunings, and undergoes an abrupt rotation through 90° for detunings close to resonance. The distribution of populations in the magnetic sublevels of the 1P1 state can be estimated using a simple model …

Fine‐Structure Mixing Within The Zn(43pj) Multiplet By Collisions With The Noble Gases, Xianming Han, J. F. Kelly

Xianming Han

Measurements of rate coefficients for intramultiplet state transfer of Zn(4 ³ P ₁→4 ³ P _J’) by collisions with the rare gases are presented. The state‐to‐state binary rate coefficients are derived from least‐squares fittings of the time‐resolved triexponential behavior of the 4 ³ P ₁fluorescence. These rate coefficients were studied systematically over a temperature range of 690–1100 K in order to characterize the velocity dependence of the collisional coupling. The systematic behavior of the rate coefficients with varying temperature and noble gas species is qualitatively consistent with a nearly adiabatic coupling limit for noncrossing levels.

Spin-Exchange Cross Section For Electron Excitation Of Na 3s 3p Determined By A Novel Spectroscopic Technique, Xianming Han, G. W. Schwinn, A. Gallagher

Xianming Han

An experimental technique is described which enables determination of the partial cross sections for electron excitation of atoms as a function of changes in spin and orbital angular momentum. This method provides a good signal-to-noise ratio in the energy region near threshold, and could be used to study long- or short-lived excited states of many atomic systems. Measurements for Na 3S−3P, near-threshold excitation are reported here. The results are generally in good agreement with the close-coupling calculations of D. L. Moores and D. W. Norcross [J. Phys. B 5, 1482 (1972)] for the largest ΔmS and ΔmL components of the …

Superfluorescence From Optically Trapped Calcium Atoms, Xianming Han

Xianming Han

We have studied superfluorescence (SF) under highly unfavorable conditions of rapid collisional and radiative distribution in a Doppler-broadened medium. Nanosecond SF pulses at 5.5 μm were generated on the Ca 4s4p1P1–3d4s1D2 transition from a column of calcium vapor buffered with Ar by optically pumping the 4s21S0–4s4p1P1 transition. The Rabi frequency associated with the intense pump pulse prevents the occurrence of SF while the pump laser is on. As a result, the predicted scaling laws that describe the properties of SF in a transversely excited system, such as peak heights, pulse widths, and delay times, are shown to apply in our …

A Multilayer Surface Detector For Ultracold Neutrons

Robert W. Pattie Jr.

Monoclinic Optical Constants, Birefringence, And Dichroism Of Slanted Titanium Nanocolumns Determined By Generalized Ellipsometry, Daniel Schmidt, Benjamin Booso, Tino Hofmann, Eva Schubert, Andrew Sarangan, Mathias Schubert

Andrew Sarangan

Generalized spectroscopic ellipsometry determines the principal monoclinic optical constants of thin films consisting of slanted titanium nanocolumns deposited by glancing angle deposition under 85° incidence and tilted from the surface normal by 47°. Form birefringence measured for wavelengths from 500 to 1000 nm renders the Ti nanocolumns monoclinic absorbing crystals with c-axis along the nanocolumns, b-axis parallel to the film interface, and 67.5° monoclinic angle between the aand c-axes. The columnar thin film reveals anomalous optical dispersion, extreme birefringence, strong dichroism, and differs completely from bulk titanium. Characteristic bulk interband transitions are absent in the spectral range investigated.

Unimolecular Decomposition Of Formic And Acetic Acids: A Shock Tube/Laser Absorption Study, A. Elwardany, E. F. Nasir, Et. Es-Sebbar, A. Farooq

Dr. Et-touhami Es-sebbar

The thermal decomposition of formic acid (HCOOH) and acetic acid (CH3COOH), two carboxylic acids which play an important role in oxygenate combustion chemistry, were investigated behind reflected shock waves using laser absorption. The rate constants of the primary decomposition pathways of these acids: The thermal decomposition of formic acid (HCOOH) and acetic acid (CH3COOH), two carboxylic acids which play an important role in oxygenate combustion chemistry, were investigated behind reflected shock waves using laser absorption. The rate constants of the primary decomposition pathways of these acids: HCOOH→CO+H2O (R1) HCOOH→CO2+H2 (R2) CH3COOH→CH4+CO2 (R3) CH3COOH→CH2CO+H2O (R4) were measured using simultaneous infrared laser …

Laser-Wakefield Accelerators: Glass-Guiding Benefits, Donald P. Umstadter

Donald P. Umstadter

A main attraction of laser-driven electron accelerators is their absence of cavity walls, which can break down in the presence of intense electric fields. Now it seems that the inclusion of a hollow glass fibre cavity could lead to more efficient acceleration at lower laser intensities. ... Further research will reveal which of the above methods for guiding light will ultimately prove best for future accelerator designs. In any case, although it is perhaps ironic that the relatively old technology of glass waveguides may benefit next-generation accelerators, it is nonetheless satisfying to see such a classic photonic solution come to …

Gravitational And Electromagnetic Waves On The Null Cone, Maria Babiuc-Hamilton

Maria C. Babiuc-Hamilton

Gravitational radiation is properly defined only at future null infinity, but mathematically it is estimated at a finite radius, and then extrapolated. Our group developed a characteristic waveform extraction tool, implemented in an open source code, which computes the gravitational waves infinitely far from their source, in terms of compactified null cones, by numerically solving Einstein equation. We add electromagnetic waves to the null cone, by deriving a formulation of the Einstein-Maxwell equations suitable to be numerically implemented into a characteristic code, that will evolve and calculate both the gravitational waves and their electromagnetic counterparts all the way to infinity.

Well-Posedness Of Characteristic Evolution In Bondi Coordinates, Maria Babiuc-Hamilton, Jeff Winicour

Maria C. Babiuc-Hamilton

Gravitational waves carry information about their source, and their detection will uncover facets of our universe, otherwise invisible. Recently, we made publicly available a waveform computation tool, the PITT code, as part of the Einstein Toolkit open software for relativistic astrophysics. The code implements the “characteristic method,” which computes the gravitational waves infinitely far from their source in terms of compactified light cones. We proved that our code produces waveforms that satisfy the demands of next generation detectors. However, the main problem is that the well-posedness of the Einstein equations in characteristic formulation is not proven. Here we present our …

On-Chip Multi 4-Port Optical Circulators, Ramy El-Ganainy, Miguel Levy

Ramy El-Ganainy

We present a new geometry for on-chip optical circulators based on waveguide arrays. The optical array is engineered to mimic the Fock space representation of a noninteracting two-site Bose–Hubbard Hamiltonian. By introducing a carefully tailored magnetooptic nonreciprocity to these structures, the array operates in the perfect transfer and surface Bloch oscillation modes in the forward and backward propagation directions, respectively. We show that an array made of ð2N þ 1Þ waveguide channels can function as N 4-port optical circulators with very large isolation ratios and low forward losses. Numerical analysis using beam propagation method indicates a large bandwidth of operation.

Light Transport In Pt-Invariant Photonic Structures With Hidden Symmetries, M. H. Teimourpour, Ramy El-Ganainy, A. Eisfeld, A. Szameit, Demetrios N. Christodoulides

Ramy El-Ganainy

We introduce a recursive bosonic quantization technique for generating classical PT photonic structures that possess hidden symmetries and higher order exceptional points. We study light transport in these geometries and we demonstrate that perfect state transfer is possible only for certain initial conditions. Moreover, we show that for the same propagation direction, left and right coherent transports are not symmetric with field amplitudes following two different trajectories. A general scheme for identifying the conservation laws in such PT-symmetric photonic networks is also presented.

Exceptional Points And Lasing Self-Termination In Photonic Molecules, Ramy El-Ganainy, M. Khajavikhan, Li Ge

Ramy El-Ganainy

We investigate the rich physics of photonic molecule lasers using a non-Hermitian dimer model.We show that several interesting features, predicted recently using a rigorous steady-state ab initio laser theory (SALT), can be captured by this toy model. In particular, we demonstrate the central role played by exceptional points (EPs) in both pump-selective lasing and laser self-termination phenomena. Due to its transparent mathematical structure, our model provides a lucid understanding for how different physical parameters (optical loss, modal coupling between microcavities, and pump profiles) affect the lasing action. Interestingly, our analysis also confirms that, for frequency mismatched cavities, operation in the …

On-Chip Non-Reciprocal Optical Devices Based On Quantum Inspired Photonic Lattices, Ramy El-Ganainy, A. Eisfeld, Miquel Levy, Demetrios N. Christodoulides

Ramy El-Ganainy

We propose integrated optical structures that can be used as isolators and polarization splitters based on engineered photonic lattices. Starting from optical waveguide arrays that mimic Fock space (quantum state with a well-defined particle number) representation of a non-interacting two-site Bose Hubbard Hamiltonian, we show that introducing magneto-optic nonreciprocity to these structures leads to a superior optical isolation performance. In the forward propagation direction, an input TM polarized beam experiences a perfect state transfer between the input and output waveguide channels while surface Bloch oscillations block the backward transmission between the same ports. Our analysis indicates a large isolation ratio …

Supersymmetric Mode Converters, Matthias Heinrich, Mohammad-Ali Miri, Simon Stützer, Ramy El-Ganainy, Stefan Nolte, Alexander Szameit, Demetrios N. Christodoulides

Ramy El-Ganainy

Originally developed in the context of quantum field theory, the concept of supersymmetry can be used to systematically design a new class of optical structures. In this work, we demonstrate how key features arising from optical supersymmetry can be exploited to control the flow of light for mode division multiplexing applications. Superpartner configurations are experimentally realized in coupled optical networks, and the corresponding light dynamics in such systems are directly observed. We show that supersymmetry can be judiciously utilized to remove the fundamental mode of a multimode optical structure, while establishing global phase matching conditions for the remaining set of …

Application Of Transfer Matrix Method To Secondharmonic Generation In Nonlinear Photonic Bandgap Structures: Oblique Incidence, Han Li

Han Li

No abstract provided.

Early Rayleigh-Scatter Lidar Temperature Measurements From The Lower Thermosphere, Leda Sox, Vincent B. Wickwar

Leda Sox

Rayleigh-scatter lidar observations were made on many clear nights at the Atmospheric Lidar Observatory (ALO) at Utah State University (USU) from 1993 to 2004 in the altitude range 45–90 km. An upgraded facility, 66 times more sensitive, has been brought on line. It has resulted in temperature measurements with maximum altitudes that extend into new territory—the lower thermosphere. All-night temperature averages have been recorded up to an altitude of 114 km. Temperatures from each month, starting in June 2014, are presented and discussed. They are compared to each other, to the ALO-USU climatology from the original lidar, and to temperatures …

Nanoparticle Plasmonics: Going Practical With Transition Metal Nitrides, U. Guler, V. M. Shalaev, A. Boltasseva

U. Guler

Promising designs and experimental realizations of devices with unusual properties in the field of plasmonics have attracted a great deal of attention over the past few decades. However, the high expectations for realized technology products have not been met so far. The main complication is the absence of robust, high performance, low cost plasmonic materials that can be easily integrated into already established technologies such as microelectronics. This review provides a brief discussion on alternative plasmonic materials for localized surface plasmon applications and focuses on transition metal nitrides, in particular, titanium nitride, which has recently been shown to be a …

Sucralose Destabilization Of Protein Structure.Pdf, Nimesh Shukla

Nimesh Shukla

No abstract provided.

Sucralose Destabilization Of Protein Structure, Lee Chen, Nimesh Shukla, Inha Cho, Erin F. Cohn, Erika A. Taylor, Christina M. Othon

Erika A. Taylor, Ph.D.

Sucralose is a commonly employed artificial sweetener that behaves very differently than its natural disaccharide counterpart, sucrose, in terms of its interaction with biomolecules. The presence of sucralose in solution is found to destabilize the native structure of two model protein systems: the globular protein bovine serum albumin and an enzyme staphylococcal nuclease. The melting temperature of these proteins decreases as a linear function of sucralose concentration. We correlate this destabilization to the increased polarity of the molecule. The strongly polar nature is manifested as a large dielectric friction exerted on the excited-state rotational diffusion of tryptophan using time-resolved fluorescence …

Sensitive And Ultra-Fast Species Detection Using Pulsed Cavity Ringdown Spectroscopy, Et-Touhami Es-Sebbar

Dr. Et-touhami Es-sebbar

Pulsed cavity ringdown spectroscopy (CRDS) is used to develop a novel, ultra-fast, high-sensitivity diagnostic for measuring species concentrations in shock tube experiments. The diagnostic is demonstrated by monitoring trace concentrations of ethylene in the mid-IR region near 949.47 cm−1. Each ringdown measurement is completed in less than 1 μs and the time period between successive pulses is 10 μs. The high sensitivity diagnostic has a noise-equivalent detection limit of 1.08 x 10−5 cm−1 which enables detection of 15 ppm ethylene at fuel pyrolysis conditions (1845 K and 2 bar) and 294 ppb ethylene under ambient conditions (297 K and 1 …

Importance And Reliability Of Small Basis Set Ccsd(T) Corrections To Mp2 Binding And Relative Energies Of Water Clusters, Berhane Temelso, Carla Renner, George Shields

Berhane Temelso

MP2 describes hydrogen-bonded systems well, yet a higher-order electron correlation correction in the form of a CCSD(T) calculation is usually necessary to achieve benchmark quality energies. We evaluated the importance and reliability of small basis set CCSD(T) corrections to MP2(δCCSD(T)) both on the binding (ΔE) and relative (ΔΔE) MP2 energies for a large number of systems including four water dimer stationary points and 57 other clusters up to undecamers, (H2O)11. By comparing the MP2 energies with CCSD(T) and the explicitly correlated MP2-F12 energies with variants of CCSD(T)-F12 using different basis sets, we were able to establish that the correction to …

Plasmonics On The Slope Of Enlightenment: The Role Of Transition Metal Nitrides, U. Guler, A. Kildishev, A. Boltasseva, V. Shalaev

U. Guler

The key problem currently faced by plasmonics is related to material limitations. After almost two decades of extreme excitement and research largely based on the use of noble metals, scientists have come to a consensus on the importance of exploring alternative plasmonic materials to address application-specific challenges to enable the development of new functional devices. Such a change in motivation will undoubtedly lead to significant advancements in plasmonics technology transfer and could have a revolutionary impact on nanophotonic technologies in general. Here, we report on one of the approaches that, together with other new material platforms, mark an insightful technology-driven …

Second-Harmonic Generation At Oblique Angles In Photonic Bandgap Structures, Han Li

Han Li

No abstract provided.

Spin-Exchange Optical Pumping At High Xenon Densities And Laser Fluxes: Principles And Practice, Boyd M. Goodson, Nicholas Whiting, Hayley Newton, Jason G. Skinner, Kaili Ranta, Panayiotis Nikolaou, Michael J. Barlow, Eduard Y. Chekmenev

Nicholas Whiting

Hyperpolarization Methods For Mrs, Boyd M. Goodson, Nicholas Whiting, Aaron M. Coffey, Panayiotis Nikolaou, Fan Shi, Brogan M. Gust, Maxwell E. Gemeinhardt, Roman Shchepin, Jason G. Skinner, Jonathan R. Birchall, Michael J. Barlow, Eduard Y. Chekmenev

Nicholas Whiting

Photodissociation Of Bulk Nitrobenzene At 250, 266, And 280 Nm Using A Picosecond Laser.Pdf, Chakree Tanjaroon, Christopher J. Lue, Scott Reeve, Susan D. Allen, J. Bruce Johnson

Scott Reeve

No abstract provided.