Comparisons of spectra determined using detector atoms and spatial correlation functions

Abstract

We show how two level atoms can be used to determine the local time dependent spectrum. The method is used in a one-dimensional cavity. The spectrum obtained is compared with the mode spectrum determined using spatially filtered second-order correlation functions. The spectra obtained using two level atoms give identical results with the mode spectrum. One benefit of the method is that only one time averages are needed. It is closely related to a realistic spectrum measurement.     

A simple demonstration of the Pancharatnam phase as a geometric phase

Abstract

To demonstrate the Pancharatnam phase as a geometric (Berry's) phase, each polarization state must be obtained by projecting the previous state on it. We describe a simple interferometric arrangement for such a demonstration which only uses a single rotation linear analyser to introduce a continuously variable phase difference between the two beams.     

Emission Spectra of a Two-level Atom Under the Presence of Another Two-level Atom

Abstract

We investigate the spectrum of light emitted by a two-level atom interacting with another two-level atom inside an ideal cavity within the frame of generalized Jaynes-Cummings model. The influence of various ratios of the coupling constants of the atoms to the field on the spectrum of the emitted light is studied in detail for the case when the atoms are supposed to be initially in the excited state and the field in a Fock state as well as their superposition.     

The Evolution of Correlations in a Dissipative System

Abstract

We examine the decay of two correlated atoms to a reservoir prepared in its ground state and in a squeezed multimode vacuum state. We calculate the entropies for the atoms and use the index of correlation to show the decay and regeneration of correlations between the atoms as they interact with the reservoir.     

An Optical Lock-in Technique as Applied to an Acousto-optic Integrated Spectrum Analyser

Abstract

A new signal coding technique is presented here for use with the existing integrated optical spectrum analyser structure. Modifications to the basic device are implemented, and shown to have a theoretical and an experimental dynamic range increase of 10–20 decibels (dB). Such an increase would bring the overall device dynamic range to 40–50 dB.     

Possible ionization of mercury atoms by elastic reflection in hyperthermal surface ionization experiments

An elastic collision model baed on data given by Danon et al. [Phys. Rev. Lett. 65, 2038 (1990)] was used to calculate the ionization potential of mercury atoms (V′) at the critical charge transfer distance as a function of the kinetic energy of the atoms (E). The linear dependence V′(E) obtained supports the model of surface ionization of mercury atoms by elastic reflection from a surface. Pis’ma Zh. Tekh. Fiz. 25, 42–45 (July 26, 1999)     

He Atoms Adsorbed in Carbon Nanotubes and Nanotube Bundles

We calculate the energetics of ⁴He and ³He atoms in the presence of one, two, and three carbon single-walled nanotubes (SWNTs). The spectrum is obtained for three characteristic sites: inside a tube in the presence of other tubes, within an interstitial channel, and in a groove. Calculations have been performed using both an axially symmetric averaged helium-carbon potential and for a potential constructed as a sum of individual carbon-helium interactions. Thermodynamic properties of helium atoms adsorbed in carbon nanonotube bundles are then studied using the single-particle spectrum. A range of one-dimensional (1D) to two-dimensional (2D) behavior is observed.     

Bragg Cell Diffraction in Resonant Cavities

Abstract

Steier et al. [1] have shown that the diffraction efficiency of a stationary grating may be improved by placing the grating in a resonant cavity. In this paper we describe the diffraction of light by a Bragg cell in a resonant cavity. Large improvements in diffraction efficiency are shown to be possible if scattering losses on the surface of the cell can be kept small. The effects of introducing gain into the cavity are calculated and the changes in bandwidth, resolution and dynamic range are discussed for the system when used as a radiofrequency spectrum analyser. A multichannel fibre optic system has been designed and is described.     

Quantum evaporation from the free surface of superfluid4He

The scattering of atoms and rotons at the free surface of superfluid⁴He is studied in the framework of linearised time dependent mean field theory. The phenomenological Orsay-Trento density functional is used to solve numerically the equations of motion for the elementary excitations in presence of a free surface and to calculate the flux of rotons and atoms in the reflection, condensation, and evaporation processes. The probability associated with each process is evaluated as a function of energy, for incident angles such that only rotons and atoms are involved in the scattering (phonon forbidden region). The evaporation probability forR ⁺ rotons (positive group velocity) is predicted to increase quite rapidly from zero, near the roton minimum, to 1 as the energy increases. Conversely the evaporation fromR ^– rotons (negative group velocity) remains smaller than 0.25 for all energies. Close to the energy of the roton minimum, , the mode-change processR ⁺ R ^– is the dominant one. The consistency of the results with general properties of the scattering matrix, such as unitarity and time reversal, is explicitly discussed. The condensation of atoms into bulk excitations is also investigated. The condensation probability is almost 1 at high energy in agreement with experiments, but it lowers significantly when the energy approaches the roton minimum in the phonon forbidden region.     

Low-noise bimodal all-fibre sensor using depolarized light

Abstract

A low-noise scheme for an all-fibre bimodal sensor is presented. Depolarized excitation of the sensor from a lower coherency source is used to eliminate polarimetric noises which inevitably arise due to polarizer/analyser and fibre-to-fibre misalignments. The sensor features simplicity and simultaneous detection of the X- and Y-polarized interference signals. Overall noise level as low as 0.8% is achieved.     

Energy-Band Structure Features of Some Crimped-Shape Nanotubes

Abstract

Energy spectra of four stereoregular carbon quasi-1D-macromolecules with polyhedral elementary units containing 60 or 58 atoms were calculated by the crystalline orbital method in the valence approach. The EHT (see R. Hoffmann, J. Chem. Phys. 1963, 39, 1397) with standardized weighted non-diagonal elements of the matrix Hamiltonian was used. Atomic coordinates of the elementary units of carbon systems under consideraton were determined as a result of energy optimization of conforming trimers by the MNDO/PM3 methods. Geometries of inner monomers were used for modeling macromolecule structures. It was found that the widths of energy gaps of three systems [C₆₀]_n under consideration are located in the interval from 1.3 to 1.5 eV. Besides, quasi-localized energy levels were found in the spectrum gaps of these carbon quasi-1D-systems.     

Calculation of voltage fluctuation caused by intermittent loads

Abstract

Intermittent loads, such as grinders and welders, are the main factors that degrade the power quality in the distribution system. Intermittent loads will result in voltage fluctuations with stochastic characteristics, which may lead to malfunction of other sensitive loads. This paper uses cumulant method to calculate the bus voltage fluctuation using the algebraic addition and multiplication. The probability density function of the voltage fluctuation can be further expressed by the Gram‐Charlier series expansion. Compared with traditional methods, computation complexity can be simplified and computation time can be markedly reduced by the proposed method. The simulation results from an 11‐bus industrial distribution system with grinders show the applicability of the proposed method.     

THE REACTION OF C60F20 WITH ANTHRACENE: FORMATION OF AN OXIDISED-ANTHRACENE 1 : 1 COMPLEX

ABSTRACT

The reaction of C₆₀F₂₀ (“Saturnene”) with anthracene yields a white 1?:?1 cycloadduct (1) in which two oxygen atoms have inserted into the anthracene framework due to fullerene-catalysed oxidation; the ¹⁹F NMR spectrum of the product shows evidence of through-cage homoconjugation.     

Determination of the ordered distribution of aluminum atoms in a zeolitic framework. Part II

The connectivity-configuration matrices method, developed in Part I, is applied to mordenite (Na₈Al₈Si₄₀O₉₆) to determine the ordered distribution of Al atoms in its framework. There are, in such a high-siliceous zeolite, hundreds of candidates which well describe an observed ²⁹Si MAS n.m.r. spectrum. By utilizing dependencies of various properties of mordenite on the Al content, only one configuration pattern of Al atoms can be selected from these candidates.The reason is sought for why only one pattern is realized out of hundreds of candidates. For this purpose a new rule is introduced complementing Loewenstein's AlOAl avoidance rule, i.e., that a five-membered ring cannot contain two Al atoms. The new rule directly gives a correct configuration of Al atoms as the unique solution using ²⁹Si MAS n.m.r. spectrum alone. The rule is further applied to ferrierite and others, giving correct values for the maximum amounts of Al atoms contained in them. The limitation of applicability of the new rule is discussed.     

A comparison of methods for the computer modelling of crystal structures

Summary Two different methods have been used to simulate the structures of three-dimensional polymeric systems and tested on silica sodalite SiO, and nine metal oxides (VO, VO₂ (rutile and distorted rutile), V₂O₃ (corundum), TiO, TiO₂ (rutile), TiO, (anatase), -PbO₂ and NiNb₂O₆). The first method uses traditional molecular mechanics. The structure is considered to be covalent and a large fragment is built consisting of ca. 500 atoms. Force-field parameters are then derived to reproduce the structure as accurately as possible. The edge atoms are fixed during the simulation. The second method employs the ionic structure model, where no bonds are included. Periodic boundary conditions are used and the Ewald summation is employed to calculate Coulombic energy. Van der Waals parameters are optimised to reproduce the crystal structure. Results show that the ionic structure model is more successful for oxides with distorted or irregular bonding. However, simple regular structures are modelled equally well by both methods.Supplementary material available from the authors: One table with nonbonded parameters, associated with formal charges, for the metal oxides, optimised via the PARAM program.     

Second Harmonic Generation as a Tool for Measuring Mode Coupling,Pulse Length and Mode Size in Short Laser Pulses

Abstract

We report on a detailed analysis of second harmonic generation with a multi-modal beam for a non-collinear geometry. As a result some improvements for a picosecond pulse width analyser are suggested. Experimental results relative to both a free electron laser and to a mode locked Nd: YAG laser are discussed. This modified version of the pulse analyser is able to monitor, in real time, the relative pulse-to-pulse change of mode size, pulse length and mode mixing effect independently of the pulse length from femtoseconds to milliseconds.     

The Fabry-Perot Interferometer. History,Theory, Practice and Applications

Abstract

A simple algebraic algorithm is proposed as a computational tool for the thin-lens design of a triplet which consists of a singlet and a cemented doublet. The triplet is required to yield specified amounts of lens power, primary spherical aberration, central coma, longitudinal chromatic aberration and secondary spectrum. The three element powers of the triplet are first obtained by solving the simultaneous linear equations of the total lens power, longitudinal chromatic aberration and secondary spectrum. A quadratic equation is obtained by combining the equations of spherical aberration and central coma, and the lens shapes are then obtained by solving this quadratic equation. The solving process is purely algebraic and is therefore easy to calculate and guarantees that all the solutions can be found.     

The Casimir Effect in Dielectrics

Abstract

The Casimir force in one dimension between two dielectrics with arbitrary position-dependent refractive index is calculated. A numerical procedure is developed, including renormalization and regularization, to calculate this force and the temperature correction. The force is directly derived from the electromagnetic mode structure and the corresponding eigenenergy spectrum. Some essential differences between one- and three-dimensional results are discussed.     

The Effect of Roton Backflow on Quantum Evaporation from Superfluid 4He

We investigate the effect of roton backflow on the scattering of atoms, rotons and phonons at the free surface of superfluid ⁴ He at T=0 K by including backflow semi-phenomenologically in the form of a backflow potential in the theory of Sobnack et al. [M. B. Sobnack, J. C. Inkson, and J. C. H. Fung, Phys. Rev. B 60, 3465 (1999)]. We assume that all the surface scattering processes are elastic and that the quasiparticles and atoms are incident obliquely to the free surface. We calculate probabilities for the various one-to-one surface scattering processes allowed for a range of energies and compare the scattering rates with those obtained when backflow is neglected.     

Intracavity Optical Bistability Driven by Squeezed Light from a Parametric Amplifier

Abstract

We describe the theory of optical bistability when atoms are collectively excited within the cavity of a parametric oscillator. Both optical bistability and parametric amplification can squeeze significantly the cavity-field quantum noise. When they are coupled together we find significant changes both on the mean value bistability and on the spectrum of squeezing as the parametric coupling increases. These are calculated directly from the appropriate master equation for the density matrix using a quantum distribution function (positive P) to develop Fokker—Planck and Ito equations.