Analysis of Threshold Current and Wall-Plug Efficiency of Diode Lasers with Asymmetric Facet Reflectivity

Threshold current and differential quantum efficiency of broad contact lasers with asymmetric facet reflectivity are discussed with the purpose to reveal factors essential for optimisation of the wall-plug efficiency of such lasers. Lasers with low front facet reflectivity and short cavity often exhibit behaviour difficult to explain with a classical theory. More rigorous calculation performed in this work show that differential quantum efficiency is indeed less affected by a change of the front facet reflectivity or cavity length than predicted by such theory. These findings greatly simplify criteria for optimisation of the wall-plug efficiency of broad contact lasers with coated facets.     

Microstructure and magnetic properties of bulk amorphous and nanocrystalline Fe61Co10Zr2.5Hf2.5Nb2W2B20 alloy

The microstructure and magnetic properties, i.e. the initial magnetic susceptibility, its disaccommodation, core losses and approach to ferromagnetic saturation of the bulk amorphous and partially crystallized Fe₆₁Co₁₀Zr_2.5Hf_2.5Nb₂W₂B₂₀ alloy are studied. From X-ray, Mössbauer spectroscopy and electron microscopy studies we have stated that all samples in the as-quenched state are fully amorphous. However, after annealing the samples at 850 K for 30 min the crystalline α-FeCo grains embedded in the amorphous matrix are found. Moreover, from Mössbauer spectra analysis we have stated that the crystalline phase in those samples exhibits the long-range order. The alloy in the as-quenched state shows good thermal stability of the initial magnetic susceptibility. Furthermore, the intensity of the magnetic susceptibility disaccommodation in the rod is lower than in the ribbon. It is due to low quenching rate during the rod preparation which involves the reduction of free volumes. From the analysis of the isochronal disaccommodation curves, assuming the Gaussian distribution of relaxation times, we have found that activation energies of the elementary processes responsible for this phenomenon range from 1.2 to 1.4 eV. After the annealing of the samples the initial susceptibility slightly enhances and disaccommodation drastically decreases. From high-field magnetization studies we have learned that the size of structural defects depends on the quenching rate (the shape of the samples) and changes after annealing.     

Microstructure investigations and magnetic after-effect in amorphous and nanocrystalline Fe–Zr–Ti–B–Cu alloy

The microstructure evolution and low field magnetic properties i.e. initial magnetic susceptibility, stabilization field and magnetic after-effect as disaccommodation of the amorphous and nanocrystalline Fe₈₀Zr₄Ti₃B₁₂Cu₁ alloy were investigated. The heat treatment of the as-quenched Fe₈₀Zr₄Ti₃B₁₂Cu₁ alloy at 773 K for 1 h leads to its nanocrystallization. It was stated that initial magnetic susceptibility increases and intensity of disaccommodation decreases with increasing of annealing temperature. The magnetic after-effect of the investigated nanocrystalline samples is connected with relaxation processes that occur in the amorphous matrix.     

Proton femtoscopy at STAR

The analysis of two-particle femtoscopy provides a powerful tool to study the properties of matter created in heavy ion collisions. Applied to identical and nonidentical hadron pairs, it makes the study of space-time evolution of the source in femtoscopic scale possible. Baryon femtoscopy allows extraction of the radii of produced sources which can be compared to those deduced from identical pion studies, providing additional information about source characteristics. In this paper we present the correlation functions obtained for protons and antiprotons for Au + Au collisions √s _NN = 62.4 and 200 GeV. On the other hand, as STAR experiment participates in Beam Energy Scan program, we present theoretical predictions of p − p, [`(p)] - [`(p)]\bar p - \bar p and p - [`(p)]p - \bar p femtoscopic measurements, based on UrQMD simulation for √s _NN = 5–39 GeV.     

Microstructure and some magnetic properties of bulk amorphous (Fe0.61Co0.10Zr0.025Hf0.025Ti0.02W0.02B0.20)100−xYx (x=0, 2, 3 or 4) alloys

Microstructure, revealed by X-ray diffraction, transmission electron microscopy and Mössbauer spectroscopy, and magnetic properties such as magnetic susceptibility, its disaccommodation, core losses and approach to magnetic saturation in bulk amorphous (Fe_0.61Co_0.10Zr_0.025Hf_0.025Ti_0.02W_0.02B_0.20)_100−xY_x (x=0, 2, 3 or 4) alloys in the as-cast state and after the annealing in vacuum at 720 K for 15 min. are studied. The investigated alloys are ferromagnetic at room temperature. The average hyperfine field induction decreases with Y concentration. Due to annealing out of free volumes its value increases after the heat treatment of the samples. The magnetic susceptibility and core losses point out that the best thermal stability by the amorphous (Fe_0.61Co_0.10Zr_0.025Hf_0.025Ti_0.02W_0.02B_0.20)₉₇Y₃ alloy is exhibited. Moreover, from Mössbauer spectroscopy investigations it is shown that the mentioned above alloy is the most homogeneous. The atom packing density increases with Y concentration, which is proved by the magnetic susceptibility disaccommodation and approach to magnetic saturation studies.     

Plans for correlation studies for BES program at RHIC

We present an overview of the main concepts concerning correlation studies for the Beam Energy Scan Program at STAR. QGP signatures at higher RHIC energies are the most obvious example of the creation of a new state of matter. In order to learn more about the transition to this state and to find a possible location of a critical point between a first-order transition and cross-over area, a new program dedicated to such analyses is formulated. Correlation studies are one of the most important obervables of the scanning of unknown region of the phase diagram. Measurements of elliptic flow, local parity violation in strong interactions, azimuthally-sensitive correlations as well as two-proton femtoscopy and nonidentical particle correlations are discussed in this paper.     

Magnetization behavior and magnetocaloric effect in bulk amorphous Fe60Co5Zr8Mo5W2B20 alloy

Microstructure by X-ray diffraction and Mössbauer spectroscopy, and isothermal magnetic entropy changes in the bulk amorphous Fe₆₀Co₅Zr₈Mo₅W₂B₂₀ alloy in the as-quenched state and after annealing at 720 K for 15 min are studied. The as-cast and heat treated alloy is paramagnetic at room temperature. The quadrupole splitting distribution is unimodal after annealing indicating the more homogenous structure in comparison with that for the as-cast alloy. Curie temperature slightly increases after annealing from 265±2 K in the as-quenched state to 272±2 K and the alloy exhibits the second order magnetic phase transition. The maximum of isothermal magnetic entropy changes appears at the Curie points and is equal to 0.30 and 0.42 J/(kg·K) for the alloy in the as-quenched state and after annealing, respectively. In the paramagnetic region the material behaves as a Curie-Weiss paramagnet.