Influence of shifted phase value on the output spectra of DFB lasers with phase shifter

DFB lasers with π/2 phase shifter can run stably on single mode and providevery high side mode suppression ratio (MSR). This attractive feature may be degraded ifphase shift deviates from π/2. In this paper, we analyze theoretically how the output spectraand side mode suppression ratio are influenced by the deviation value of phase shift from π/2.     

Calculation of the phase diagram of the TiZr alloy and investigation of the tendency toward separation of the ω phase

The electronic, structural, and thermodynamic properties of the TiZr equiatomic alloy have been calculated in terms of the electron density functional theory and Debye-Grüneisen model. The calculated lattice parameters a and c/a agree well with experimental data for the α, ω, and β phases. It has been shown that the ω phase is stable at atmospheric pressure and low temperatures, and it remains energetically more favorable up to T = 600 K. In the temperature range 600 K < T < 900 K, the α phase becomes stable, and above 900 K, the β phase of the TiZr alloy is stable. The phase diagram constructed in this study agrees qualitatively with the available experimental data. A tendency toward separation of the TiZr equiatomic alloy in the ω phase has been analyzed. It has been demonstrated that, in the ground state, the TiZr equiatomic alloy in the ω phase exhibits a tendency toward ordering rather than toward phase separation.     

The prompt phase mechanism of gamma-ray bursts

Gamma-ray bursts(GRBs)are flashes of ganima-rays occurring at cosmological distances(for a recent review see^[1]).They are divided into two classes based on their prompt emission durations:short-duration(<2 seconds)hard-spectrum bursts and long-duration soft-spectmm bursts(>2 seconds).The observations(including discoveries of both the gravitational wave event GW170817 from an inspiral of two neutron stars and its electromagnetic counterparts)indicate that long-duration GRBs result from core collapses of massive stars and short-duration GRBs are produced from mergers of neutron star-neutron star binaries or black hole-neutron star binaries.     

Temperature-induced phase transition of two-dimensional semiconductor GaTe

GaTe is a two-dimensional Ⅲ-Ⅵ semiconductor with suitable direct bandgap of~1.65 eV and high photoresponsivity,which makes it a promising candidate for optoelectronic applications.GaTe exists in two crystalline phases:monoclinic(m-GaTe,with space group C2/m) and hexagonal(h-GaTe,with space group P63/mmc).The phase transition between the two phases was reported under temperature-varying conditions,such as annealing,laser irradiation,etc.The explicit phase transition temperature and energy barrier during the temperature-induced phase transition have not been explored.In this work,we present a comprehensive study of the phase transition process by using first-principles energetic and phonon calculations within the quasi-harmonic approximation framework.We predicted that the phase transition from h-GaTe to m-GaTe occurs at the temperature decreasing to 261 K.This is in qualitative agreement with the experimental observations.It is a two-step transition process with energy barriers 199 meV and 288 meV,respectively.The relatively high energy barriers demonstrate the irreversible nature of the phase transition.The electronic and phonon properties of the two phases were further investigated by comparison with available experimental and theoretical results.Our results provide insightful understanding on the process of temperature-induced phase transition of GaTe.     

Quantum phase transition of the Jaynes-Cummings model

Herein, we propose an experimentally feasible scheme to show the quantum phase transition of the Jaynes-Cummings(JC) model by modulating the transition frequency of a two-level system in a quantum Rabi model with strong coupling. By tuning the modulation frequency and amplitude, the ratio of the effective coupling strength of the rotating terms to the effective cavity(atomic transition) frequency can enter the deep-strong coupling regime, while the counter-rotating terms can be neglected. Thus, ...     

Carrier-envelope phase of ultrashort pulsed Laguerre-Gaussian beam

The carrier-envelope phase of the ultrashort pulsed Laguerre-Gaussian beam is studied.The order of Laguerre function affects seriously the variations of the carrier-envelope phase with the propagation dis- tance increasing.The beam waist also affects the carrier-envelope phase in a few Rayleigh distances.The variation of the carrier-envelope phase is larger on the axis than on the beam periphery in propagation.     

Experimental verification of combinational-deformable-mirror for phase correction

In adaptive optics (AO) system,the phase compensation capability is limited greatly by the actuator num- ber of the deformable mirror (DM).The actuator number of DM is mainly restricted by the manufacture techniques.The spatial correction capability of AO system can be improved by two or more combinational- DMs (CDMs) with conjugation relationship.The CDM AO system for wavefront correction is built,which consists of two 32-element DMs.The experimental results are in agreement with the numerical simulation results.It is indicated that the CDM AO system provides better correction performance than the single 32-element DM AO system.     

Generation of phase nuclei by solitons of the new “undulator” type in martensitic phase transitions of crystalline materials

The microdynamics of large-amplitude nonlinear lattice vibrations of plutonium and uranium materials has been investigated at high reactor temperatures in the ranges of martensitic phase transitions. Topologically new large-amplitude solitons of the “undulator” type have been revealed. Transverse and longitudinal “undulator” solitons in crystals with hexagonal and cubic symmetry, depending on the direction of motion, have different kinematic and amplitude characteristics, which differ from the characteristics of the previously known solitons. The transverse “undulator” solitons, like electrons in undulators, are observed with periodic atomic displacements orthogonal to the direction of soliton propagation. The longitudinal “undulator” solitons with displacements of atoms in the direction of soliton propagation are characterized by periodic delays with two-step velocities on the trajectory in a certain analogy with two-period engineering undulator devices. It has been shown that, at high energies, such “undulator” solitons of two types generate nuclei of a new phase in early stages of structural phase transitions.     

The meaning of the terms “phase” and “phase transition”

Various meanings of the terms phase and phase transition encountered in scientific literature are discussed. These terms supplement each other and cover only together all the macroscopic situations which are now denoted by this term.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 67–71, August, 1988.     

The study of phase matching of nonlinear waves in microdroplets

In this paper, the internal field distribution of higher order MDRs of water droplets is calculated and the result shows that the higher order MDRs should dominate the nonlinear couple process. Furthermore, the phase matching required for four-wave mixing (FWM) process in the droplet is interpreted as the concept of angular momentum conservation. The slight mismatch in angular momentum leads to significant improvement of phase matching than that in optical cell.     

Can an electric field induce an antiferroelectric phase out of a ferroelectric phase?

It has been widely accepted that electric fields favor the ferroelectric phase with parallel electric dipoles over the antiferroelectric phase. With detailed measurements in polycrystalline ceramics of Pb(0.99)Nb(0.02[(Zr(0.57)Sn(0.43)(1-y)Ti(y)](0.98)O(3), we demonstrate in this Letter that electric fields can induce an antiferroelectric phase out of a ferroelectric phase, i.e., trigger an apparently unlikely ferroelectric-to-antiferroelectric phase transition. We suggest that it is caused by the volume contraction from the converse piezoelectric effect at the coercive field with a reversed polarity.     

Symmetry systematics of pressure—induced phase transitions

Abstract

Most pressure induced phase transitions are diffusionless. Because of this, there exists a one-to-one correspondence between the positions of atoms in the parent and the product phases, which, therefore, show interesting symmetry relationships. In this paper, we have used these for discussing a symmetry classification of pressure induced phase transitions into four categories: iso-symmetric, group-subgroup, intersection group, and order-disorder transitions. Various examples illustrating this classification scheme are discussed. The importance of this classification is in understanding the mechanism of pressure indbced phase transitions, where both theoretical calculations and experimental measurements are employed to analyse related phenomena like softening of phonon modes, elastic instabilities, diffraction patterns, and orientation relations.     

The deforraable mirror method of adaptive phase correction

In this paper, a simple method of phase correction by using a micromachined deformable mirror (MMDM) is demonstrated. With correction of high-order phases due to propagating through medium, we obtained a clean pulse shape, flattened spectral phase and decreased the femtosecond laser pulse duration. It is shown by our experiment that the deformable mirror is an effective and easy method for adaptive phase correction.     

The phase structure of Einstein–Cartan theory

In the Einstein–Cartan theory of torsion-free gravity coupling to massless fermions, the four-fermion interaction is induced and its strength is a function of the gravitational and gauge couplings, as well as the Immirzi parameter. We study the dynamics of the four-fermion interaction to determine whether effective bilinear terms of massive fermion fields are generated. Calculating one-particle-irreducible two-point functions of fermion fields, we identify three different phases and two critical points for phase transitions characterized by the strength of four-fermion interaction: (1) chiral symmetric phase for massive fermions in strong coupling regime; (2) chiral symmetric broken phase for massive fermions in intermediate coupling regime; (3) chiral symmetric phase for massless fermions in weak coupling regime. We discuss the scaling-invariant region for an effective theory of massive fermions coupled to torsion-free gravity in the low-energy limit.     

Non-collinear phase of a singlet–triplet magnet

The spin subsytem of copper oxides within the model of polar singlet–triplet Jahn–Teller centers is described by the Hamiltonian of a singlet–triplet magnet with multiparametric (non)collinear spin arrangements. Using the modified mean-field approximation we analyze the conditions of an appearance of the non-collinear phase. Certain static and dynamic properties of the new phase are considered.     

Correlations of conserved charges and QCD phase structure

Correlations of conserved charges,i.e.,the baryon number,electric charge,and strangeness,are calculated at finite temperature and chemical potentials up to the fourth order.The calculations are done ina 2+1 flavor low energy effective theory,in which the quantum and thermal fluctuations are encoded through the evolution of flow equations within the functional renormalization group approach.Strangeness neutrality and a fixed ratio of the electric charge to the baryon number density are implemented throughout the computation.We find that higher-order correlations incorporate more sensitive critical dynamics than the quadratic ones.In addition,a non-monotonic dependence of the fourth-order correlations between the baryon number and strangeness,i.e.,-χ₃₁^BS/χ₂^Sand χ₂₂^BS/χ₂^S,on the collision energy is also observed.     

The contribution of order to the phase stability of β-Cu-Zn-Al

We report the lower stability temperatures, T(β), of the body centred cubic (bcc) β phase for several alloys along the line of compositions Cu(0.76-0.5x)-Zn(x)-Al(0.24-0.5x), corresponding to a constant electron to atom ratio e/a = 1.48. The results have been obtained by means of differential scanning calorimetry measurements at various heating rates. The influence of atomic ordering on the stability of the bcc structure was evaluated using a mixed approach involving Monte Carlo simulations and the cluster variation method. It was found that the chemical short- and long-range ordering contributes to the free energy of the alloy by an amount of around 200k(B).     

Elasticity of the B2 phase and the effect of the B1–B2 phase transition on the elasticity of MgO

A study of the high-pressure anisotropy of MgO was conducted using first-principles calculations based on density functional theory within the generalized gradient approximations. The pressure dependence of the elastic stiffness coefficients and the anisotropy parameters, in both B1 and B2 phases, shows that for high-hydrostatic compression the easiest deformation is the shear along (100) plane and the the material's response to deformation and to shearing strains is quite the same. According to the calculations of the velocities of propagation of elastic waves, we deduced that MgO develop an elastic anisotropy, especially, in the B1 phase. We present the B2 phase elastic properties which are not already studied under high pressure.     

Influence of pressure on the solid state phase transformation of Cu-Al-Bi alloy

The solid state phase transformation of Cu-Al-Bi alloy under high pressure was investigated by x-ray diffraction, energy dispersive spectroscopy and transmission electron microscopy. Experimental results show that the initial crystalline phase in the Cu-Al-Bi alloy annealed at 750℃ under the pressures in the range of 0-6 GPa is α-Cu solid solution (named as α-Cu phase below), and high pressure has a great influence on the crystallisation process of the Cu-Al-Bi alloy. The grain size of the α-Cu phase decreases with increasing pressure as the pressure is below about 3 GPa, and then increases (P 3 GPa). The mechanism for the effects of high pressure on the crystallisation process of the alloy has been discussed.     

Thermal phase change and activation energy of crystallization of Ge-Sb-Te-Sn thin films

To improve the optical storage performance, Sn was doped into Ge2Sb2Te5 phase change thin films. The optical and thermal properties of Sn-doped Ge2Sb2Te5 film were investigated. The crystal structures of the as-sputtered and the annealed films were identified by the X-ray diffraction (XRD) method. The differential scanning calorimeter (DSC) method is used to get the crystallization temperature and crystallization energy (Ea). It was found that proper Sn-doping could highly improve storage performance of the Ge2Sb2Te5 media.