Semiclassic Models of the Dissipative Regime of Instability and Superradiation of a Quantum Radiator System

The paper discusses the similarity between dissipative generation and superradiance regimes for systems of excited quantum emitters placed in an open cavity. In the case of the existence of a resonator field due to reflections from the ends of the system, a dissipative generation regime is usually realized. In this case, the decrement of oscillations in the waveguide in the absence of radiators turns out to be greater than the increment of the arising instability of the system of radiators placed in the resonator. When describing this mode, the influence of the emitters on each other and the sum of their own fields is neglected. The resonator field forces the oscillators to emit or absorb quanta synchronously with it, depending on the local value of the population inversion. Lasing takes on a weakly oscillatory character due to an asynchronous change in the population inversion of the system of emitting dipoles (nutations), which have a ground and excited energy levels. To describe the process, the equations of the semiclassical theory based on the use of the density matrix are quite sufficient. In the case when there is no resonator or waveguide field, taking into account the eigenfields of the oscillators becomes essential. To simulate the superradiance process, large emitting particles are used, to describe which one should use the equations for the density matrix. It is shown that the interaction of quantum emitters in this case is due to electromagnetic fields under conditions when the overlap of their wave functions is insignificant. Equations are obtained that allow considering the process of interaction of emitters. When the emitters interact, an integral field is formed in the resonator, an increase in the intensity of which leads to synchronization of the emitters. It is shown that the characteristic times of the development of the process, as well as the attainable amplitudes of the excited fields for dissipative regimes of generation and regimes of superradiance of emitters filling an open resonator, are comparable.

Mode-Converting Corrugations for Cavities of Second-Harmonic Gyrotrons with Improved Performance

Mode-converting longitudinal corrugations are used as a means of improving the selectivity properties of cavities for second-harmonic gyrotrons. As an example, 100-kW 0.3-THz second-harmonic gyrotron is considered. For the operating second-harmonic mode and most dangerous first-harmonic competing modes, the eigenvalues, ohmic losses and beam-wave coupling coefficients are investigated with respect to dimensions of a corrugated cavity. The most optimal parameters are found for a gyrotron cavity with mode-converting corrugations, which ensure the widest range of a single mode operation for the 0.3-THz second-harmonic gyrotron. It is shown that, in this range, the gyrotron output power can be increased up to 180 kW. It is found that output mode purity of the 0.3-THz second-harmonic gyrotron falls off due to mode-converting corrugations, which induce undesirable coupling of the operating mode with neighboring Bloch harmonics in the output section of the gyrotron cavity.

Modeling and Simulation of Lead-Free Perovskite Solar Cell Using SCAPS-1D

In this work, the effect of some parameters on tin-based perovskite (CH3NH3SnI3) solar cell were studied through device simulation with respect to adjusting the doping concentration of the perovskite absorption layer, its thickness and the electron affinities of the electron transport medium and hole transport medium, as well as the defect density of the perovskite absorption layer and hole mobility of hole transport material (HTM). A device simulator; the one-dimensional Solar Cells Capacitance Simulator (SCAPS‑1D) program was used for simulating the tin-based perovskite solar cells. The current-voltage (J-V) characteristic curve obtained by simulating the device without optimization shows output cell parameters which include; open circuit voltage (Voc) = 0.64V, short circuit current density (Isc) = 28.50mA/, fill factor (FF) = 61.10%, and power conversion efficiency (PCE) = 11.30% under AM1.5 simulated sunlight of 100mW/cm2 at 300K. After optimization, values of the doping concentration, defect density, electron affinity of electron transport material and hole transport material were determined to be: 1.0x1016cm-3, 1.0x1015cm-3, 3.7 eV and 2.3 eV respectively. Appreciable values of solar cell parameters were obtained with Jsc of 31.38 mA/cm2, Voc of 0.84 V, FF of 76.94% and PCE of 20.35%. when compared with the initial device without optimization, it shows improvement of ~1.10 times in Jsc, ~1.80 times in PCE, ~1.31 times in Voc and ~1.26 time in FF. The results show that the lead-free CH3NH3SnI3 perovskite solar cell which is environmentally friendly is a potential solar cell with high theoretical efficiency of 20.35%.

Structure and Properties of ZnSnP2 With the Application in Photovoltaic Devices by Using CdS and ZnTe Buffer Layers

Ab initio calculations have been performed by the linearized augmented plane wave (LAPW) method as implemented in the WIEN2K code within the density functional theory to obtain the structural, electronic and optical properties of ZnSnP2 in the body centered tetragonal (BCT) phase. The six elastic constants (C11, C12, C13, C33, C44 and C66) and mechanical parameters have been presented and compared with the available experimental data. The thermodynamic calculations within the quasi-harmonic approximation is used to give an accurate description of the pressure-temperature dependence of the thermal-expansion coefficient, bulk modulus, specific heat, Debye temperature, entropy Grüneisen parameters. Based on the semi-empirical relation, we have determined the hardness of the material; which attributed to different covalent bonding strengths. Further, ZnSnP2 solar cell devices have been modeled; device physics and performance parameters have analyzed for ZnTe and CdS buffer layers. Simulation results for ZnSnP2 thin layer solar cell show the maximum efficiency (22.9%) with ZnTe as the buffer layer. Most of the investigated parameters are reported for the first time.

How the Limit Values Work

The efficiency of limiting quantities as a tool for describing physics at various spatio-temporal scales is shown. Due to its universality, limit values allow us to establish relationships between, at first glance, distant from each other's characteristics. The article discusses specific examples of the use of limit values to establish such relationships between quantities at different scales. Based on the principle of reaching the limiting values on the event horizons, a connection was obtained between the Planck values and the values of the Universe. The resulting relation can be attributed to relations of the Dirac type - the coincidence of large numbers that emerged from empirical observations. In the article, the relationships between large numbers of the Dirac type are established proceeding, in a certain sense, from physical principles - the existence of limiting values. It is shown that this ratio is observed throughout the evolution of the Universe. An alternative way of solving the problem of the cosmological constant using limiting values and its relation to the minimum spatial scale is discussed. In addition, a one-parameter family of masses was introduced, including the mass of the Universe, the Planck mass and the mass of the graviton, which also establish relationships between quantities differing by 120 orders of magnitude. It is shown that entropic forces also obey the same universal limiting constraints as ordinary forces. Thus, the existence of limiting values extends to informational limitations in the Universe. It is fundamentally important that on any event horizon, regardless of its scale (i.e., its gravitational radius), the universal value of limit force c4/4G is realized. This allows you to relate the characteristics of the Universe related to various stages of its evolution.

Study of Structural and Electronic Properties of Intercalated Transition Metal Dichalcogenides Compound MTiS2 (M = Cr, Mn, Fe) by Density Functional Theory

In the present work, we have studied intercalated Transition Metal Dichalcogenides (TMDC) MTiS2 compounds (M = Cr, Mn, Fe) by Density Functional Theory (DFT) with Generalized Gradient Approximation (GGA). We have computed the structural and electronic properties by using first principle method in QUANTUM ESPRESSO computational code with an ultra-soft pseudopotential. A guest 3d transition metal M (viz; Cr, Mn, Fe) can be easily intercalated in pure transition metal dichalcogenides compound like TiS2. In the present work, the structural optimization, electronic properties like the energy band structure, density of states (DoS), partial or projected density of states (PDoS) and total density of states (TDoS) are reported. The energy band structure of MTiS2 compound has been found overlapping energy bands in the Fermi region. We conclude that the TiS2 intercalated compound has a small band gap while the doped compound with guest 3d-atom has metallic behavior as shown form its overlapped band structure.

Surface Purity Effect on Irregularities of Changes in Deformation Texture of Zr-2.5% Nb Alloy

This work is a continuation of a series of works on the study of regularities and structural mechanisms of changes in characteristics of crystallographic texture during cold deformation of plates made of Zr2.5%Nb alloy. Effects of influence of surface cleanliness of the plates on the textural regularities during their rolling were investigated. For this, longitudinal fragments of the tube Æ15.0´1.5 mm² were used, flattened, annealed at 580°C in a vacuum of 1.5...3.0 Pa and rolled along the axis of the original tube with various degrees deformation up to 56%, which is likened to longitudinal rolling of plates. Techniques of maximally uniform straightening of tube fragments were used. An analysis of the results of studies of textural changes during cross rolling of plates, straightened from rings of the same tube and pretreated under similar conditions, is also carried out. To analyze the results, the method of inverse pole figures was used, which, in these studies, is distinguished by the possibility of achieving satisfactory accuracy in calculating the integral characteristics of texture. On this basis, the Kearns textural coefficient was calculated along the normal to the plates’ plane. Corrections were introduced for texture dissimilarity along the thickness of the plates, which is caused by the unbending of the preliminary blanks. Additionally, the analysis of texture distributions was carried out using original techniques. According to the results obtained – as a result of X-ray measuring from the plates’ surface – oscillations of the course of changes in the texture coefficient were revealed. This is associated with an alternating process of relaxation of residual stresses during deformation. It has been established that this effect is initiated from the near-surface regions, is associated with a near-surface impurity, and in some cases can penetrate to a considerable depth of the plates. The twinning nature of such regularities is confirmed and active systems of twins are noted.

Empirical Relation for Electronic and Optical Properties of Binary Tetrahedral Semiconductors

The concept of ionicity has been developed by Phillips and Van Vechten from the dielectric analysis of the semiconductors and insulators to evaluate various bond parameters of binary tetrahedral (AIIBVI and AIIIBV) semiconductors. In this paper, an advance hypothesis of average atomic number of the elements in a compound has been used to evaluate intrinsic electronic and optical parameters such as ionic gap (Ec), average energy gap (Eg), crystal ionicity (fi) and dielectric constant (ϵ) of binary tetrahedral semiconductors.

Optoelectronic Properties of Ternary Tetrahedral Semiconductors

The dielectric interpretation of crystal ionicity evolved by Phillips and Van Vechten (P.V.V) has been utilized to evaluate various ground state properties for broad range of semiconductors and insulators. Although, the relevance of P.V.V dielectric theory has been restricted to only simple ANB8-N structured compounds, which have a particular bond. Levine has broadened P.V.V. theory of ionicity to multiple bond and complex crystals and evaluated many bond parameters for ternary tetrahedral semiconductors. Some other researchers have extended Levine’s work with a concept of ionic charge product and nearest neighbour distance to binary and ternary tetrahedral crystals to evaluate the ground state properties. In this paper, a new hypothesis of average atomic number of the elements in a compound has been used to understand the some electronic and optical properties such as ionic gap (Ec), average energy gap (Eg), crystal ionicity (fi), electronic susceptibility (χ), and dielectric constant (ϵ) of ternary tetrahedral (AIIBIV and AIBIII) semiconductors. A reasonably acceptable agreement has been noticed between our evaluated values and other researchers reported values.