Transport of Nonautonomous Solitons in Two‐Dimensional Disordered Media

Transport of localized nonlinear excitations in disordered media is an interesting and important topic in modern physics. Investigated in this work is transport of two‐dimensional (2D) solitons for a nonlinear Schrödinger equation with inhomogeneous nonlocality and disorder. We use the variational method to show that, the shape (size) of solitons can be manipulated through adjusting the nonlocality, which, in turn, affects the soliton mobility. Direct numerical simulations reveal that the influence of disorder on the soliton transport accords with our analysis by the variational method. Besides, we have demonstrated an anisotropic transport of the 2D nonautonomous solitons as well. Our study is expected to shed light on modulating solitons through material properties for specifying their transport in disordered media.     

Three‐Dimensional,Time‐Resolved Profiling of Ferroelectric Domain Wall Dynamics by Spectral‐Domain Optical Coherence Tomography

We apply here spectral‐domain optical coherence tomography (SD‐OCT) for the precise detection and temporal tracking of ferroelectric domain walls (DWs) in magnesium‐doped periodically poled lithium niobate (Mg:PPLN). We reproducibly map static DWs at an axial (depth) resolution down to ～ 0.6 μm, being located up to 0.5 mm well inside the single crystalline Mg:PPLN sample. We show that a full 3‐dimensional (3D) reconstruction of the DW geometry is possible from the collected data, when applying a special algorithm that accounts for the nonlinear optical dispersion of the material. Our OCT investigation provides valuable reference information on the DWs’ polarization charge distribution, which is known to be the key to the electrical conductivity of ferroelectric DWs in such systems. Hence, we carefully analyze the SD‐OCT signal dependence both when varying the direction of incident polarization, and when applying electrical fields along the polar axis. Surprisingly, the large backreflection intensities recorded under extraordinary polarization are not affected by any electrical field, at least for field strengths below the switching threshold, while no significant signals above noise floor are detected under ordinary polarization. Finally, we employed the high‐speed SD‐OCT setup for the real‐time DW tracking upon ferroelectric domain switching under high external fields.     

Tunable Wide‐Bandwidth Resonators Based on Layered Gallium Sulfide

Wide‐bandwidth and high‐frequency operation are the two desired properties from resonators in a wide range of applications, such as communication devices, energy harvesters, inertial sensors, and electronic components. However, achieving both of these prerequisites along with detectable vibration amplitudes is very challenging. Herein, nano‐electromechanical resonators based on layered gallium sulfide (GaS) are demonstrated. These resonators show resonance frequencies in the range of 10–25 MHz under ambient conditions and a bandwidth of hundreds of kilohertz, which can be simply tuned by predetermining the dimensions of the devices. Therefore, this study emphasizes that, in addition to excellent performances in electronic and optoelectronic applications, GaS can also be implemented as a high performance core element in nanoresonator applications.     

Influence of a Magnetic Field on the Nonlinear Optical Susceptibility of NiI2-Doped CdI2 Single Crystals

The influence of treatment in a magnetic field at low temperatures on the nonlinear optical properties of NiI₂-doped CdI₂ single crystals is investigated. The impurity ions in the interlayer space or more complex centers into which these ions enter can align on exposure to a magnetic field due to the interaction with the membrane vibrations of the lattice and create residual polarization in a specimen. This polarization causes redistribution of the electric charge on the bonds and improves the nonlinear optical properties of single crystals.     

MREI‐model calculations of Raman‐active modes in layered mixed crystals TiS2−xSex(0≤x≤2)

A modified random‐element isodisplacement model has been developed and used to calculate the concentration dependence of the wavenumbers of Raman‐active modes in mixed crystal system, TiS_2−xSe_x(0≤x≤2). Earlier theoretical work, based on the Jaswal model, predicted a phase transition in this system on cooling up to 125 K temperature for the composition x ≥ 1.2. But recently reported resistivity measurements did not find the existence of any phase transition for a composition x < 1.4 on cooling. Our calculations show these findings and give remarkably better fitting to Raman data. The estimated values of the force constants are found to lie generally in the range 10⁵–10⁶ amu cm⁻². Copyright © 2007 John Wiley & Sons, Ltd.     

The Scattering Problem in PT‐Symmetric Periodic Structures of 1D Two‐Material Waveguide Networks

A PT‐symmetric periodic structure with two‐material waveguide networks is constructed. In this study, how changing the number of cells affects the transmission properties is investigated. The results show that the PT‐unbroken (broken) region of the system is only determined by the cell structure, regardless of the number of unit cells. This means that any system has the same exceptional points (EPs), regardless of the number of cells and as long as the cell structure is consistent. In addition, it is confirmed that the coherent perfect absorbers and lasers (CPA lasers) occur in our model. The transfer matrix method is used to derive a sufficient condition for achieving the CPA laser point. A simple, effective formula for predicting the CPA laser state in an N unit cell system is derived.     

Optical properties and radiation effects in layered crystals of (CnH2n+nNH3)2MCl4: n = 1, 2, 3; M = Cd,Cu, Mn

Abstract

A new absorption band has been found at 5.10 eV in (C _n H_{2n + 1}NH₃)₂CdCl₄: n = 1, 2, 3 in addition to the absorption bands of CdCl₂ whose electronic structure resembles the former crystals. The energy of the additional peak shifts with temperature by as much as 0.38 eV from 5.10eV at room temperature (RT) to 5.48 eV at liquid nitrogen temperature. This large peak shift is attributed to a structural phase transition between these two temperatures. A new type of electron center has been found in these crystals (M = Cd, Mn; n = 1, 2, 3) irradiated with X-rays at 15 K in addition to the Cl₂ ^?. This shows optical absorption bands (IR bands) in the infrared region of 10 ～ 20 kcm ^?1. The IR bands are assigned to an electron center where an electron is trapped at an ammonium site in the neighborhood of a Cl^? vacancy.     

Unity‐Order Nonlinear Optical Index Change in Epsilon‐Near‐Zero Composite Materials of Gain Media and Metal Nanoparticles

This work reports giant optical nonlinearity of active gain composites containing metal nanoparticles. In the epsilon‐near‐zero regime, the effective index of the composite strongly depends on the magnitude of host material's saturable gain and one can obtain unity‐order nonlinear optical index change for the pump with gain saturation intensity. For pump intensity of about 100 kW/cm², the nonlinear refractive index (the refractive index change per unit pump intensity) reaches 10^?5 cm²/W, which is 6–8 orders‐of‐magnitude larger than the records recently obtained in epsilon‐near‐zero bulk materials. If the gain value of the host medium is slightly larger than a critical value, such large optical nonlinearity can be obtained without loss or even accompanying with amplification. The proposed materials also have the advantage of wide tunability of operating wavelength range from visible to infrared by changing the gain value of the host and the shape parameters and filling factors of metal nanoparticles.     

High Intensity Generation of Entangled Photons in a Two‐Mode Electromagnetic Field

At present, the sources of entangled photons have a low rate of photon generation. This limitation is a key component of quantum informatics for the realization of such functions as linear quantum computation and quantum teleportation. In this paper, we propose a method for high intensity generation of entangled photons in a two‐mode electromagnetic field. On the basis of exact solutions of the Schrödinger equation, when electrons interact in an atom with a strong two‐mode electromagnetic field, it is shown that there may be large quantum entanglement between photons. The quantum entanglement is analyzed on the basis of the Schmidt parameter. It is shown that the Schmidt parameter can reach very high values depending on the choice of characteristics of the two‐mode fields. We find the Wigner function for the considered case. Violation of Bell's inequalities for continuous variables is demonstrated.     

4‐Phenyl‐1,2,4‐triazoline‐3,5‐dione in the ene reactions with cyclohexene, 1‐hexene and 2,3‐dimethyl‐2‐butene. The heat of reaction and the influence of temperature and pressure on the reaction rate

The values of the enthalpy (53.3; 51.3; 20.0 kJ mol^?1), entropy (?106; ?122; ?144 J mol^?1K^?1), and volume of activation (?29.1; ?31.0; ?cm³ mol^?1), the reaction volume (?25.0; ?26.6; ?cm³ mol^?1) and reaction enthalpy (?155.9; ?158.2; ?150.2 kJ mol^?1) have been obtained for the first time for the ene reactions of 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione 1 , with cyclohexene 4 , 1‐hexene 6 , and with 2,3‐dimethyl‐2‐butene 8 , respectively. The ratio of the values of the activation volume to the reaction volume (?V^≠_corr/ΔV_{r ? n}) in the ene reactions under study, 1 + 4 → 5 and 1 + 6 → 7 , appeared to be the same, namely 1.16. The large negative values of the entropy and the volume of activation of studied reactions 1 + 4 → 5 and 1 + 6 → 7 better correspond to the cyclic structure of the activated complex at the stage determining the reaction rate. The equilibrium constants of these ene reactions can be estimated as exceeding 10¹⁸ L mol^?1, and these reactions can be considered irreversible. Copyright © 2014 John Wiley & Sons, Ltd.