Optical Double-resonance Spectra with Time-dependent Pulses

Abstract

The optical double-resonance spectrum for a three-level atom interacting with two monochromatic laser pulses with arbitrary temporal profiles is calculated by use of Light's perturbation theory. Unlike some earlier work, the theory is not restricted to exact resonance of the pump laser, or to pulse areas which are exact multiples of 2π. A variety of pulse profiles are investigated, and the spectra are found to depend strongly on the detuning of the pump laser.     

Equivalence of interaction hamiltonians in the electric dipole approximation

Abstract

The interaction of an atomic system with an externally applied electromagnetic field can be treated in the electric dipole approximation by means of either the minimal coupling (p · A) or direct coupling (d · E) Hamiltonian. It is shown that both methods lead to identical and unambiguous predictions for observable quantities as long as the atomic wavefunctions are transformed when used in the minimal-coupling formulation. The physical meaning of kinetic momentum is used to show that the atomic states must be described by wavefunctions calculated in the absence of an electromagnetic field when using the d · E (but not the p · A) form of the interaction Hamiltonian. When, however, observables are calculated using the common approximations of resonance atomic physics – the two-level approximation and the rotatingwave approximation – the two formulations can lead to measurably different results. This point is illustrated by calculating the induced polarization (and hence the refractive index) of an atomic system for the two exactly soluble cases of the harmonic oscillator and the hydrogen atom.     

Laser Pulse Shape Effects in Harmonic Generation from a Two-level Atom

Abstract

The harmonic spectrum emitted by a two-level atom driven by a resonant laser field is calculated. The spectrum is seen to depend on the shape of the pulse. In the case of an asymmetric pulse profile, harmonic emission is present also at a relatively low intensity field.     

Resonance Fluorescence in a Squeezed Vacuum

Abstract

Fluorescence from a coherently driven two-level atom that is damped by a squeezed vacuum is studied. We show that the mean atomic polarization depends on the relative phases of the squeezed vacuum and the coherent driving field. The fluorescent spectrum is calculated and shows several modifications over the spectrum for normal resonance fluorescence. In particular, the central peak of the Mollow triplet has a linewidth that depends on the phase of the driving field. For strong squeezing this peak can either be much narrower or much broader than the natural linewidth of the atom.     

Non-classical Features in the Three-level Jaynes-Cummings Model

Abstract

The eigenfunctions and eigenenergies of the system composed of a cascade three-level atom and bichromatic or monochromatic field with arbitrary detunings are presented. The development of the state vector of the system with arbitrary initial conditions is obtained. The development of the quantum fluctuations and the second-order coherence degree for the field is calculated. The dependence of the squeezing and antibunching on the detunings, initial intensities and initial squeezing is studied. The contribution of single-photon and two-photon transitions to, and the influence of, the a.c. Stark effect on the squeezing are discussed.     

Thermodynamic calculations for precipitation in maraging steels

Abstract

In the present work, thermodynamic calculations for several maraging systems have been carried out, and the results are compared with experimental data. The calculations were conducted using ThermoCalc. Excellent agreement is obtained between calculation and experimental measurements using mainly the atom probe. As a highlight, calculated equilibrium phases and their mole fractions in 1RK91 steel recently developed by Sandvik compare extremely well with atom probe microchemistry data, which showed the presence of copper rich particles, mixed Ni₃Al and Ni₃Ti, and molybdenum rich precipitates. Calculations also indicate the thermodynamic stability of μphase in the Fe–Ni–Mo and Fe–Ni–Co–Mo systems, Ni₃Al and Ni₃Ti in a chromium containing steel, and NiMn in a Fe–Ni–Mn system. However, it should be noted that thermodynamic calculations may only be used as a guideline for systems not in equilibrium.     

Atom probe characterisation of high temperature materials

Abstract

An atom probe is capable of quantitatively analysing materials at the atomic level. Modern atom probes are derived from the field ion microscope, and are coupled with time-of-flight mass spectrometers, permitting identification of individual atoms. The introduction of position-sensitive detectors enables the reconstruction of a small volume of the sample owing to simultaneous determination of the x, y, and zcoordinates and the mass to charge ratios of individual atoms. This paper focuses on the application of atom probe techniques to the microstructural analysis of high temperature materials. Illustrations include carbide precipitation in creep resistant power plant steels and analyses of model and commercial multicomponent nickel based superalloys. It is demonstrated that atom probe field ion microscopy and atom probe tomography are valuable techniques in the development and understanding of technologically important alloys for high temperature service.     

Level Crossing in a Frequency-dependent Photon Reservoir

Abstract

The level-crossing effect for a three-level atom placed into the resonant cavity (waveguide) and illuminated by a strong monochromatic laser light is discussed. The cavity plays the role of a frequency-dependent photon reservoir that modifies the spontaneous decay of the atom. The effect is studied by considering the modifications of the level-crossing (Hanle effect) signals. The non-Markovian character of spontaneous emission in frequency-dependent reservoirs is taken into account. Calculated signals are interpreted in terms of a dressed atom picture.     

Electron entrainment current in gases bombarded with beams of fast highly-charged ions

It is shown that asymmetry in the ejection of electrons in an elementary collision event between an atom and a fast highly-charged ion may lead to a macroscopic effect, the electron entrainment current, when a gas target is bombarded by a beam of fast highly-charged ions. The entrainment current is calculated for the bombardment of a helium target by a 25 MeV/u Mo⁴⁰⁺ beam. Pis’ma Zh. Tekh. Fiz. 24, 62–65 (September 26, 1998)     

The location of atomic hydrogen in NiTi alloy: A first principles study

A first principles density functional theory study to investigate the H defect in NiTi alloy is presented. We have determined the interstitial H atom position in bulk B2 phase NiTi alloy. H positions on both the Ti and Ni terminated NiTi surfaces are calculated. Surface adsorptions of H atom on Ni/Ti terminated surfaces are calculated for a low surface coverage of 1.96 × 10¹⁴ cm^?2. We have also calculated the penetration barrier energy for an H atom from the surface site to the bulk lattice site.     

Generalized master equation for a two-level atom in a strong field and tailored reservoirs

Abstract

The generalized master equation for a two-level atom driven by a strong classical field and damped into a ‘tailored’ reservoir with a non-flat density of modes is derived under the Born-Markov approximation. To derive the master equation the dressing transformation on the atomic operators is performed first and next the dressed operators are coupled to the reservoir and the corresponding damping rates are calculated. The modifications introduced by a strong field and/or by the reservoir with the non-flat density of modes lead to non-standard terms in the master equation, some of which are reminiscent of terms known for squeezed vacuum reservoirs. The optical Bloch equations based on this generalized master equation are obtained and solved for the steady state. The solutions are discussed from the point of view of both bare and dressed atoms. Analytical formulas for the fluorescence and probe absorption spectra are obtained and illustrated graphically.     

Preparation of two-mode anticorrelated photon-number state via atom de Broglie wave deflection

Abstract

It is shown that the deflection of an atom de Broglie wave at two adjacent cavities containing non-resonant weak fields can yield a highly entangled quantum state of the atom–field system in which discernible atomic beams are entangled to internal states of the atom and to two-mode photon-number states of the fields. Two-mode anticorrelated entangled photon-number states characterized by the total photon number can be prepared by the detection of the atom in given directions of the propagation.     

A scheme for the simultaneous measurement of atomic position and momentum

Abstract

We propose an optical scheme for the simultaneous measurement of the position and momentum of a single atom. The scheme involves the coupling of the atom of two light fields with different spatial and polarization characteristics. The proposed technique is closely related to the Arthurs-Kelly measurement scheme; the principal difference is that in the present case the values of the position and momentum are inferred from phase shifts in electromagnetic fields rather than from shifts in the position of a pointer.     

Carbon solubilities in iron at elevated temperatures analysed by statistical thermodynamics

Abstract

Carbon solubilities in iron at elevated temperatures (>1000 K) are analysed on the basis of statistical thermodynamics. A parameter Q which refers to the extent of stabilization of a carbon atom in the iron lattice is estimated for α-, γ-, and molten FeC_x phases. The results suggest that the carbon atom is most stable in molten FeC_x and least stable in (α-FeC_x. In addition, the value of Q_C^α for (α-FeC_x at high temperatures appears to be different from that at lower temperatures. This observation can be interpreted as the effect of the magnetic transition of the iron atom around the Curie temperature. The values for Q estimated for the other interstitial elements X (X = H, N, P, S) in iron lattices are compared.

MST/586     

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.     

Application of advanced analytical techniques to study structure–property relationship of hot rolled high strength low alloy steel

Abstract

The microstructure–property relationship in conventional high strength low alloy (HSLA) steel was evaluated using data obtained from transmission electron microscopy (TEM) and atom probe tomography (APT). Atom probe tomography allowed the characterisation of fine TiC particles with average radius of 3±1·2 nm that were not observed by TEM. The increase in the yield strength of steel due to the presence of fine precipitates was calculated to be 128 MPa.     

The Interaction of Displaced Number State and Squeezed Number State Fields with Two-level Atoms

Abstract

The time-evolution of a single two-level atom in a single-mode high-Q cavity is sensitive to the quantum fluctuations of the cavity radiation field and to its photon statistics: this sensitivity is realizable experimentally in the Rydberg atom micromaser. We study the effects of the interaction of a two-level atom with two new non-classical radiation fields: the squeezed number state and the displaced number state realizable by nonlinear and linear transformations of field number states which have an initially precise occupation number. The time-varying field fluctuations caused by the atomic interaction are described using the Q-function quasi-probability.     

Quantum effects in the transient dynamics of a many mode Jaynes-Cummings model

Abstract

Phenomenology and mechanisms of energy exchange, due to induced atomic processes of absorption and emission, are investigated in the evolution of a two-mode Jaynes-Cummings model. One field mode is initially in a highly coherent populated state and the other one is initially empty. The field mode exchanges energy with the atom by two mechanisms, related to very different atomic dynamics, which operate in complementary phases of the system evolution. One mechanism determines the energy exchanges which involve only the populated mode and the atom. The other is responsible for mode-mode photon exchanges and becomes relevant when the first mechanism is quenched. Thus there is no competition between the atomic emission in the empty mode and processes involving the atom and the highly populated mode. Quantum features related to entanglement of atom and field states are discussed. Cooperative effects between the two field modes and their incompatibility with the predictions of neo-classical theory are evidenced.     

Monte Carlo investigation of an atom laser with a modulated quasi-one-dimensional cavity

Abstract

The dynamics of a recently proposed atom laser scheme based on a modulated quasi-one-dimensional atom cavity are investigated. A three-mode model is developed which includes the effects of dipole–dipole collisions as well as pump and loss mechanisms. It is shown that the Monte Carlo wavefunction simulation technique is superior to a direct solution of the resulting master equation because of the existence of constants of motion which are present in the Monte Carlo wavefunctions but not in the full density operator. Under suitable parameter choices, the solution to the master equation leads to Poissonian atom statistics in the occupation of a single-atomic-cavity mode, analogous to the photon statistics of the optical laser. A threshold behaviour is predicted as the losses are varied relative to the gain for the laser mode.     

Wavelet analysis of short harmonics generated in presence of a two colour laser field

Abstract

The Morlet wavelet spectrum of the radiation emitted by a two level atom in presence of two laser pulses with very close frequency is obtained. The wavelet spectrum gives information on the time evolution of the full spectrum and of a particular line. The beating condition stimulates the atom to emit pulses of harmonics with duration of the order of a few optical cycles of the pumping radiation. Pulse trains of 3 optical cycles (FWHM) are observed.