Kerr nonlinearity and optical multi-stability in a four-level Y-type atomic system

The nonlinear response to applied fields of a four-level Y-type atomic system is investigated. The effect of laser intensity and quantum interference induced by spontaneous emission on optical bistability, optical multi-stability and Kerr nonlinearity is then discussed. It is found that the threshold of the optical bistability can substantially be reduced by the quantum interference. So, an enhanced Kerr nonlinearity with reduced absorption can be achieved.     

Exhibition of subluminal solitons in a four-level atomic system with two-folded levels

With one weak probe, one strong pumping and one control field, the group velocity dispersion can be balanced by the Kerr effects in a lifetime-broadened four-level atomic medium with two folded levels with proper parameters. This results from the subluminal optical solitons that are formed. Additionally, the conditions for which subluminal solitons occur are given.     

Three-dimensional atom localization in a five-level M-type atomic system

By using three mutually perpendicular standing-wave fields, we propose a scheme for three-dimensional (3D) subwavelength atom localization in a five-level M-type atomic system. Based on the electromagnetically induced transparency, position probability distribution of the atom in 3D space could be determined via measuring the probe absorption which is proportional to the filter function. It is shown that patterns of 3D atom localization depends sensitively on the coupling schemes of the standing-wave fields. When the standing-wave fields couple three different transitions, the same atom localization patterns are formed in the eight subspaces of the 3D space. While all the standing-wave fields are applied on one transition, we can realize different atom localization patterns in the eight subspaces. From the view of the xy plane, various symmetric or asymmetric atom localization patterns could be formed at different z positions by adjusting the parameters of the laser fields.     

Control of spontaneous emission in a four-level system

Spontaneous emission in a four-level atomic system coupled by two coherent driven fields is investigated. Using a wave function technique, an explicit expression of the spontaneous emission spectrum is derived. The influence of driven fields on spontaneous emission spectra of k and q photons are investigated. The interesting phenomena including spectral line narrowing, enhancement, suppression and quenching, are observed by adjusting driven fields and detunings.     

Enhanced gain and narrow linewidth of an optical cavity by the Doppler effect in a four-level atomic system

Abstract

A scheme for high gain and narrow linewidth of an optical cavity with a four-level atomic system is proposed by the Doppler effect via active Raman gain (ARG) process. Atomic motion leads to Doppler frequency shift which induces constructive interference for the linear susceptibility. The enhanced normal dispersion greatly narrows the cavity linewidth, and the amplified gain gives rise to a high cavity transmission. Simulation results show that the cavity linewidth based on ARG is about one order of magnitude narrower than that based on electromagnetically-induced transparency under the same conditions, and the cavity transmission intensity could be enhanced by nearly 30 times.     

Coherent control of spontaneous emission in a four-level system

Abstract

In this article we study the potential for coherently control spontaneous emission in a four-level scheme. Our control parameter is the relative phase of two laser fields having the same angular frequency. We investigate in detail the trapping conditions, the population dynamics and the behaviour of the (long time) spontaneous emission spectrum, which are now phase dependent. Inhibition of spontaneous emission and extreme spectral narrowing are shown as the relative phase is varied. Our results are interpreted using a dressed state analysis of the dynamics.     

Crystal growth of alkaline earth fluorides in a reactive atmosphere

Crystal growth of MF₂ (M = Ca, Sr, or Ba) is carried out in a reactive atmosphere consisting of HF and a carrier gas (He). Single-crystal Bridgman ingots, with the axis oriented at 〈111〉, are grown up to 5.2 cm in diameter. The mechanical strength of these specimens is found to be higher than what has been reported.     

Efficient atom localization via probe absorption in an inverted-Y atomic system

The behaviour of atom localization in an inverted-Y atomic system is theoretically investigated. For the atoms interacting with a weak probe field and several orthogonal standing-wave fields, their position information can be obtained by measuring the probe absorption. Compared with the traditional scheme, we couple the probe field to the transition between the middle and top levels. It is found that the probe absorption sensitively depends on the detuning and strength of the relevant light fields. Remarkably, the atom can be localized at a particular position in the standing-wave fields by coupling a microwave field to the transition between the two ground levels.     

Divalent chromium in alkaline earth silicate systems

Journal of Materials Science -     

Phase time delay and Hartman effect in a one-dimensional photonic crystal with four-level atomic defect layer

The Hartman effect is revisited using a Gaussian beam incident on a one-dimensional photonic crystal (1DPC) having a defect layer doped with four-level atoms. It is considered that each atom of the defect layer interacts with three driving fields, whereas a Gaussian beam of width w is used as a probe light to study Hartman effect. The atom–field interaction inside the defect layer exhibits electromagnetically induced transparency (EIT). The 1DPC acts as positive index material (PIM) and negative index material (NIM) corresponding to the normal and anomalous dispersion of the defect layer, respectively, via control of the phase associated with the driving fields and probe detuning. The positive and negative Hartman effects are noticed for PIM and NIM, respectively, via control of the relative phase corresponding to the driving fields and probe detuning. The advantage of using four-level EIT system is that a much smaller absorption of the transmitted beam occurs as compared to three-level EIT system corresponding to the anomalous dispersion, leading to negative Hartman effect.     

Modification of Kerr nonlinearity in a four-level quantum system near a plasmonic nanostructure

We present a theoretical study for the Kerr nonlinearity of a four-level double-V-type quantum system near a two-dimensional array of metal-coated dielectric nanospheres. In the quantum system under study one V-type transition is influenced by the interaction with surface plasmons while the other V-type transition interacts with free-space vacuum. The quantum system interacts with a linearly polarized weak laser field that couples the lowest state with the upper states in the free-space transitions. We show that the Kerr nonlinearity is strongly influenced by the presence of the plasmonic nanostructure and is particularly sensitive to the distance between the quantum system and the plasmonic nanostructure.     

Several metastable alkaline earth feldspar modifications

Various metastable crystalline forms of alkaline earth feldspars were produced by the method of catalysed crystallisation of glass. Results obtained by differential thermal analysis and thermal expansion measurements suggest the existence of low-high displacive transformations in SrAl₂Si₂O₈ and CaAl₂Si₂O₈. The former is rapid and analogous to the one known in BaAl₂Si₂O₈ and the latter is rather sluggish. This study was carried out while the author was an employee at Corning Glass Works.     

Heterogeneous nucleation of alkaline earth feldspars in glasses

Though suitable conditions of structural geometry favouring epitaxy were demonstrated, yet it was observed that epitaxy was not a dominant and, possibly, not even an important factor in the nucleation processes studied. Indeed, the mere presence of close structural geometrical fit between the catalyst and the nucleus does not necessarily lead to epitaxy. Other factors such as the concentration of the nucleating agent in the glass and variations in the chemical composition of the glass, and their effects on the nucleation are discussed. Also the effect of the feldspar structure on the kinetic barrier for its nucleation, and several specific liquid phase separation phenomena, are evaluated.     

Valence stability of molybdenum in alkaline earth molybdates

Presence of oxygen stability range in ternary oxides was experimentally verified for molybdenum(IV) perovskites, and the widths of stability range were determined of BaMoO₃, SrMoO₃ and CaMoO₃. Moreover, the tetravalent state of molybdenum was found to be more strongly stabilized in these compounds than in its binary oxide. A concept of lattice self-potential was examined in order to explain this phenomenon. Contribution of A-cation to the retention of high valence state of B-cation in the perovskite ABO₃ was also discussed.     

Structure, nucleation and Eu luminescence in alkaline earth rare earth borate glass

In La₂O₃-MO-B₂O₃ ternary system, various glasses/ glass ceramics with M=Ca, Sr and Ba have been prepared. In this ternary system, homogeneous nucleation occuring in the B₂O₃ melt appears to be the cause for the formation of nanocrystallites, hence glass ceramics. The nucleation process is very much dependent on the alkaline earth used viz., with smaller alkaline earths like Ca, boron prefers (BO₄)⁵⁻ tetrahedral coordination with oxygen, while in the case of bigger alkaline earths like Ba and Sr, (BO₃)³⁻ triangular coordination seems to be predominant. Eu³⁺ in this glass system yields intense ⁵D₀→⁷F_j emission. A cursory view on the dependence of the various Judd-Ofelt parameters (Ω_k) indicates that Ω₂ parameter is very much dependent on the immediate vicinity of the luminescent ion (Eu³⁺) while Ω₄ is not. Various results based on these are discussed.     

The optical absorption edge of rare earth sesquisulfides and alkaline earth - rare earth sulfides

Optical band gaps were measured by diffuse reflectance spectroscopy on a series of Ln₂S₃ compounds of α, δ, ε and τ structure types and on a series of ternary sulfides MLn₂S₄ (M = Sr, Cd, Mg) of Th₃P₄, CaFe₂O₄ and spinel structure types. Sharp absorption edges are observed with band gaps ranging from 2.2 to 3.5 eV. Systematic changes occur with rare earth radii. Analysis of some of the absorption edges suggests direct forbidden transitions.     

Homogeneous and heterogeneous polymorphic transformations in alkaline earth feldspars

The displacive transformations in quartz, hexacelsian and the strontium equivalent of the latter, are homogeneous incipient transformations. These transformations are carried out mostly as a second (or higher) order reaction, and are finally completed abruptly as a first-order reaction which results from a sudden release of strain accumulated due to bond stretching. In such transformations the first-order mode of reaction seems to be eliminated to various extents by the introduction of impurities as solid solution to the structure. Such impurities promote heterogeneous transformations. The extent of sluggishness of displacive transformations and of stability relationship in alkaline earth feldspars is correlated with the various ionic sizes of barium, strontium and calcium. Displacive and diffusive transformations in alkali feldspars are also homogeneous incipient transformations, but due to the high mobility of the alkali ions, building up of strain is prevented and no abrupt change in symmetry occurs at the transformation. The hexacelsian ⇌ celsian and monotropic transformations in SrAl₂Si₂O₈ and CaAl₂Si₂O₈ are heterogeneous incipient reconstructive transformations. Differences in melting temperatures reported in the past for BaAl₂Si₂O₈ may probably be correlated with the grain size, crystalline modification and extent of Al/Si order in the sample investigated.     

Crystal growth of alkaline earth fluorides in a reactive atmosphere: Part III

A comparison of CF₄ and C₂F₄ as agents of reactive atmosphere processing (RAP) in the crystal growth of alkaline-earth fluorides is given. At temperatures much below the melting point of these metal fluorides, C₂F₄ decomposes into CF₄. CF₄ converts H₂O to HF, but has a much slower action on the dry metal oxides at ?1000°C, and, therefore, it is preferred as a secondary RAP agent to the fast-acting HF.     

Structural variations in layered alkaline earth metal cyclohexyl phosphonates

Two series of alkaline earth metal cyclohexyl phosphonates, M(C₆H₁₁PO₃H)₂(H₂O) (M = Ca, Sr and Ba) (1–3) and M(C₆H₁₁PO₃)(H₂O) (M = Mg, Ca, Sr, and Ba) (4–7) have been synthesized under mild reaction conditions. All new compounds have been characterized using elemental analysis, IR, TGA and powder X-ray diffraction techniques. The molecular structure of compound 2 determined using single crystal X-ray diffraction technique reveals a layered polymeric structure.