Absorption spectra of some radiation-doped A<Subscript>3</Subscript>B<Subscript>5</Subscript> compounds

Temperature dependences of the absorption coefficient in A₃B₅ crystals before and after irradiation by electrons with an energy of 6 MeV and a dose of Ф = 2 × 10¹⁷ electron/cm² are studied. A low-lying E_v + 0.4 eV center of a nonimpurity origin is found in both undoped GaAs crystals and those doped with various impurities (Te, Zn, Sn, Ga_1–xIn_xAs, InP, and InP〈Fe〉).     

Cohesive energy of zincblende (A<Superscript>III</Superscript>B<Superscript>V</Superscript> and A<Superscript>II</Superscript>B<Superscript>VI</Superscript>) structured solids

In this paper we present an expression relating the cohesive energy (E _coh in kcal/mol) of A^IIIB^V and A^IIB^VI semiconductors with the product of ionic charges (Z ₁ Z ₂) and nearest-neighbour distance d (Å). The cohesive energy values of these solids exhibit a linear relationship when plotted on a log-log scale against the nearest-neighbour distance d (Å), but fall on different straight lines according to the ionic charge product of the solids. A good agreement has been found between the experimental and calculated values of the cohesive energy of A^IIIB^V and A^IIB^VI semiconductors.     

Magnetoresistance of structures with MnAs layers and <Emphasis Type="Italic">A</Emphasis><Superscript>3</Superscript><Emphasis Type="Italic">B</Emphasis><Superscript>5</Superscript> semiconductors heavily doped with manganese

The magnetotransport properties of epitaxial ferromagnet/semiconductor heterostructures based on MnAs and GaMnAs ferromagnetic layers, separated by a nonmagnetic semiconductor layer (InAs or GaAs), have been investigated. Structures were obtained by combination of laser deposition and metal-organic chemical vapor deposition. A spin-valve effect was observed in magnetoresistance measurements. This fact suggests spin-polarized transport of carriers between ferromagnetic layers.     

Tunneling radiative recombination in <Emphasis Type="Italic">p-n</Emphasis> heterostructures based on gallium nitride and other A<Superscript>III</Superscript>B<Superscript>V</Superscript> semiconductor compounds

We present summarized data on the tunneling emission in p-n heterostructures based on GaN and on a series of cubic A^IIIB^V semiconductors, including GaAs, InP, GaSb, and (Ga, In)Sb. The emission in p-n heterostructures of the InGaN/AlGaN/GaN type in a spectral interval from 1.9 to 2.7 eV predominates at small currents (J<0.2 mA). The position of maximum ?ω_max in the spectrum approximately corresponds to the applied potential difference U:?ω_max=eU. The tunneling emission is related to a high electric field strength in GaN-based heterostructures. The radiative recombination probability is higher in the structures with piezoelectric fields. The observed spectra are compared to the spectra of tunneling emission from light-emitting diodes based on GaAs, InP, and GaSb. The experimental results for various semiconductors emitting in a broad energy range (0.5–2.7 eV) are described by the equation ?ω_max=eU=0.5–2.7 eV.     

Wavelength tunable femtosecond laser based on short Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> codoped phosphate fiber

A wavelength tunable laser system mode-locked by nonlinear polarization evolution based on a 3 cm-long homemade Er³⁺/Yb³⁺ codoped phosphate fiber has been reported. By simply adjusting the polarization controllers, the central wavelength of the mode-locked spectrum can be tuned over 1537.1–1563.3 nm continuously. Moreover, 264-fs pulse with 3-dB spectral width of 39.6 nm and peak power of 7.8 kW at a 7.55 MHz repetition rate is generated directly from the all-fiber ring cavity.     

Effect of the atomic composition of the surface on the electron surface states in topological insulators A<Stack><Subscript>2</Subscript><Superscript>V</Superscript></Stack>B<Stack><Subscript>3</Subscript><Superscript>VI</Superscript></Stack>

The results of the theoretical investigation of the surface electronic structure of A₂^VB₃^VI compounds containing topologically protected surface states are reported. The ideal Bi₂Te₃, Bi₂Se₃, and Sb₂Te₃ surfaces and surfaces with an absent external layer of chalcogen atoms, which were observed experimentally as monolayer terraces, have been considered. It has been shown that the discrepancy between the calculated Fermi level and the value measured in the photoemission experiments can be attributed to the presence of the “dangling bond” states on the surface of the terraces formed by semimetal atoms. The fraction of such terraces on the surface has been estimated.     

Nonlinear optical properties of Cr<Superscript>3+</Superscript>-doped laser crystals

The nonlinear optical properties in six Cr³⁺-doped laser crystals LiCaAlF₆, LiSrGaAlF₆, Gd₃Ga₅O₁₂, Gd₃Sc₂Ga₃O₁₂, LaMgAl₁₁O₁₉ and Alexandrite are investigated with the help of the Z-Scan technique at λ = 532 nm in the CW regime. The data reported here include particularly the excited state absorption cross section and the third-order nonlinear susceptibilities. It is found that the three first systems only exhibit both refractive and absorptive nonlinear effects, whereas the three others have only absorptive effects. Gd₃Ga₅O₁₂ shows the best nonlinear potentialities. The excited state absorption cross section corresponding mainly to the ⁴T₂ →   ⁴T₁ transition is found to be ranging between 8.9 × 10⁻²² cm² in LiSGaF and 3.1 × 10⁻²⁰ cm² in LaMgAl₁₁O₁₉. The calculated ratio of the third order nonlinear susceptibility to the ground state absorption coefficient is found to be largest in GGG with a value of 146 × 10⁻⁶ esu.cm and smallest in Alexandrite (0.6 × 10⁻⁶ esu.cm).     

The influence of P<Superscript>+</Superscript>, B<Superscript>+</Superscript>, and N<Superscript>+</Superscript> ion implantation on the luminescence properties of the SiO<Subscript>2</Subscript>: nc-Si system

The possible mechanisms of the influence of implanted impurities of Group III and V elements on the luminescence properties of a system consisting of silicon nanocrystals in SiO₂ are considered and generalized. The effect of boron and nitrogen ion implantation on the photoluminescence intensity is investigated experimentally. The experimental results and previously reported data on the ion-implantation doping with phosphorus are discussed in terms of the mechanisms under consideration. The state of implanted phosphorus is determined using x-ray photoelectron spectroscopy. It is shown that the enhancement and degradation of the photoluminescence depend on the type of implanted impurities and the conditions of postimplantation heat treatment.     

A ceramic based Yb<Superscript>3+</Superscript>:YAG laser

We report the performance of a laser based on a 9.8% doped ceramic Yb³⁺:YAG operating in quasi-Continuous Wave (QCW) and in Continuous Wave (CW) at room temperature. The maximum output power of 9 W with a slope efficiency of 73% at 1030 nm was achieved in QCW. We investigated the problems originated from thermo-mechanical properties of the ceramic and we studied their effects on the laser per-formance finding that either the slope efficiency or the laser threshold are thermal-losses independent. Finally, we report a characterization of a low losses tunable cavity for several laser wavelengths.     

Asymmetry of hyperfine-structure components of the 5 <Superscript>1</Superscript>S<Subscript>0</Subscript>-5<Superscript>3</Superscript>P<Subscript>1</Subscript><Superscript>113</Superscript>Cd line perturbed by argon

Experimental results of a systematic study of profiles of the hyperfine-structure components of the intercombination 5¹S₀ – 5 ³P₁ line of the even-odd ¹¹³Cd isotope perturbed by argon performed by means of a laser-induced fluorescence method are reported. We have found that the values of total line asymmetries of both hfs line components are different.     

Effect of deformation on the electronic structure and topological properties of the A<Superscript>II</Superscript>Mg<Subscript>2</Subscript>Bi<Subscript>2</Subscript> (A<Superscript>II</Superscript> = Mg,Ca,Sr,Ba) compounds

The electronic structure and topological properties of the A^IIMg₂Bi₂ (A^II = Mg,Ca,Sr,Ba) compounds are theoretically studied with the use of exact exchange. It is found that the Mg₃Bi₂ compound in the equilibrium state is a semimetal, whereas three other compounds are semiconductors with a direct fundamental band gap. It is predicted that the uniaxial deformation of three-component compounds results in transitions to topologically nontrivial phases: topological insulator and topological and Dirac semimetals. Owing to such a rich variety of topologically nontrivial phases, these compounds may be of interest for further theoretical and experimental studies.     

Tunable optical parametric oscillator based on a KTP crystal,pumped by a pulsed Ti<Superscript>3+</Superscript>:Al<Subscript>2</Subscript>O<Subscript>3</Subscript> laser

We present the characteristics of an optical parametric oscillator based on a KTP crystal, pumped with noncritical phase matching by a pulsed Ti³⁺:Al₂O₃ laser, tunable in the range 677–970 nm. Tunable generation of signal and idler waves is obtained in the ranges 1030–1390 nm and 2690–3050 nm respectively. The efficiency of conversion of the pump to the signal wave is ≈23%, which for pulses of duration ≈8 nsec ensures an energy in the range 1.0–11.5 mJ. The width of the emission spectrum for the signal wave is within the range 0.8–1.8 nm and is predominantly determined by the linewidth of the Ti³⁺:Al₂O₃ pump laser. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 351–356, May–June, 2007.     

Quasi-three level laser based on diode-pumped Nd<Superscript>3+</Superscript>:YAlO<Subscript>3</Subscript> crystal

We describe the output performances of the 930 nm ⁴ F _3/2 → ⁴ I _9/2 transition in Nd³⁺:YAlO₃ (Nd:YAP) under in-band pumping with diode laser at the 803 nm wavelength. An end-pumped Nd:YAP crystal yielded 1.13 W of continuous-wave (CW) output power for 17.8 W of incident pump power. Moreover, intracavity second-harmonic generation has also been achieved with a power of 172 mW at 465 nm by using a LiB₃O₅ (LBO) nonlinear crystal. The blue beam quality factor M ² was less than 1.3. The blue power stability was less 3% in 60 min.     

Magnetic properties of <Superscript>3</Superscript>He on the recursive lattices

We considered the Heisenberg model on the recursive lattices with multi-spin interaction in a strong magnetic field as an approximation of the two-dimensional kagome lattice, as well as hexagonal recursive lattices as an approximation of triangular lattice, for solid ³He. In a strong magnetic field it is possible to approximate the Heisenberg model with the Izing one. Using dynamic approach, we obtain exact recursion relations for partition functions. Diagrams of the magnetization versus external magnetic field with different spin-exchange parameters and temperatures are presented. Magnetization plateaux, bifurcation points, and doublings are obtained.     

A precise measurement of the B<Superscript> + </Superscript>, B<Superscript>0</Superscript> and mean b-hadron lifetime with the DELPHI detector at LEP I

Final results from the DELPHI Collaboration on the lifetime of B ⁺ and B⁰ mesons and the mean b-hadron lifetime, are presented using the data collected at the Z⁰ peak in 1994 and 1995. Elaborate, inclusive, secondary vertexing methods have been employed to ensure a b-hadron reconstruction with good efficiency. To separate samples of B ⁺ and B⁰ mesons, high performance neural network techniques are used that achieve very high purity signals. The results obtained are: and for the average b-hadron lifetime: Received: 6 October 2003, Revised: 12 December 2003, Published online: 25 February 2004     

High-power diode-cladding-pumped Tm<Superscript>3+</Superscript>, Ho<Superscript>3+</Superscript>-doped silica fibre laser

The fundamental characteristics of a continuous-wave high-power diode-pumped Tm³⁺, Ho³⁺-doped double-clad silica fibre laser are presented. A maximum output power of 5.2 W was measured and was generated at a slope efficiency of 42 (44)% with respect to the launched (absorbed) pump power. At the optimum length of 7 m (_effL=2.9, where _eff is the effective absorption coefficient of the fibre and L is the fibre length), the fibre laser output was measured to have a centre wavelength of 2105 nm and a line width of 20 nm. The centre wavelength of the emission was tunable over a 32-nm extent when 0.68<_effL<3.28 or for a 6.2-m change in L. PACS 42.55.Wd; 42.55.Xi; 42.60.Lh; 42.60.Pk     

Pressure broadening of hyperfine-structure components of the 5 <Superscript>1</Superscript>S<Subscript>0</Subscript>– 5 <Superscript>3</Superscript>P<Subscript>1</Subscript><Superscript>113</Superscript>Cd line perturbed by argon

Experimental results of a spectroscopic study of argon broadened profiles of the hyperfine-structure components of the intercombination 326.1 nm line ¹¹³Cd isotope are reported. We have found that the values of Lorentzian (collisional) widths of both hfs line components are different.     

On the processes upon the second-photon-stimulated annealing of InAs layers implanted with Be<Superscript>+</Superscript> ions

The results of the second-photon-stimulated annealing of beryllium-implanted InAs layers are presented. The hole and electron concentrations and the activation energy of second-photon-stimulated annealing are calculated for the characteristic temperature regions using thermopower voltage values measured for the implanted layer. The possible mechanisms of the annealing of radiation-induced defects and the activation of beryllium atoms are discussed.     

Revisiting B<Superscript>+</Superscript>→X(3872)+K<Superscript>+</Superscript> in pQCD assigning to X(3872) 2<Superscript>3</Superscript>P<Subscript>1</Subscript> charmonium

We revisit the B⁺→X(3872)+K⁺ in the pQCD approach assigning to X(3872) a 2³P₁ charmonium state. In this theoretical framework all the phenomenological parameters in the wavefunctions and Sudakov factor are a priori fixed by fitting other experimental data; therefore, there hardly are any free parameters in the whole numerical computations. Our results are larger than the upper bound set by the BABAR measurements. PACS 13.20.He; 12.38.Bx; 13.60.Le