High peak power Nd:YAG laser pumped by 600-W diode laser stack

The Q-switched laser with triangle slab made of Nd:YAG crystal side pumped by 600-W quasi-cw diode laser stack has been designed. The multimode (M²≈2.6) output energy of about 42 mJ was demonstrated in free running mode for110-mJ pump energy. In Q-switch experiments, the KDDP Pockels cell was placed between the slab and rear mirror in plane-plane cavity with output coupler of 84% transmission. The energy of 8 mJ in 2.1-ns pulse duration was obtained for near TEM₀₀ output beam. For passive Q-switching by means of Cr:YAG crystal of 12.6% unsaturated transmission, the energy of 5.1 mJ in 2.5-ns pulse duration was obtained for output beam close to TEM₀₀ mode.     

Preparation and semiconducting properties of Th3As4

The resistivity, thermoelectric power and Hall constant in the temperature range of 78–830 K were determined for polycrystalline Th₃As₄ samples obtained by annealing thin thorium slabs in arsenic vapour. The samples examined were n-type semiconductors with a carrier concentration ranging from 1.0 × 10¹⁸cm^?3 to 2.8 × 10¹⁸ cm^?3 for which the effective mass was found to be equal to 0.55–0.76m₀. The Hall mobility, about 450cm²V^?1s^?1 at room temperature, obeys a $\text{T}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}$ law at high temperatures. On the basis of the electrical measurements the forbidden gap of Th₃As₄ was found to be equal to 0.43 eV.     

Cauchy boundary andb-incompleteness of space-time

It is shown that if a space-time (M, g) is time-orientable and its Levi-Civita connection [in the bundle of orthonormal frames over (M, g)] is reducible to anO(3) structure, one can naturally select a nonvanishing timelike vector field and a Riemann metricg ⁺ onM. The Cauchy boundary of the Riemann space (M, g ⁺) consists of endpoints ofb-incomplete curves in (M, g); we call it theCauchy singular boundary. We use the space-time of a cosmic string with a conic singularity to test our method. The Cauchy singular boundary of this space-time is explicitly constructed. It turns out to consist of what should be expected.     

High energy,large momentum transfer amplitudes: The sum of ladder diagrams inΦ 3 theory

We perform summation of ladder diagrams in the high energy, large momentum limit. This leads to new results for both perturbative and non-perturbative approaches. In particular, an explicit expression for any diagram's contribution is given, the non-perturbative form of asymptotically non-analytic terms is found and representation of amplitude as a series of Regge poles is presented.Supported in part by Polish Ministery of National Education, grant no. CPBP 01.03     

Nucleation of Pd dimers at defect sites of the MgO(100) surface

Point defects on oxide surfaces are presumed to be preferential nucleation sites for supported metal clusters. Under typical growth conditions, dimers constitute the first step in island nucleation. First-principles calculations on the formation of Pd dimers on regular and defect sites of the MgO(100) surface show that nucleation occurs with large dimer binding energies at divacancies and charged oxygen vacancies (F+ centers), while it is less favorable on steps and neutral F centers. The extensive database of defect trapping/attachment properties gives a firm basis to rationalize recent atomic-force microscopy findings and provides guidelines valid, in general, for ionic substrates.     

Angular Distribution of Hyperfine Magnetic Field in Fe3O4 and Fe66Ni34 from Mössbauer Polarimetry

Nuclear resonance studies of the two different types impurity doped potassium hexachloro-stannates, the isomorphic system such as (K–Rb)₂SnCl₆ and K₂(Sn–Re)Cl₆ and the nonisomorphic system K₂SnCl₆:Al³⁺ in the high temperature cubic phase revealed contrasting features with one the other characterized by static in the former and dynamic feature in the latter case respectively. The resonance spectra of the nonisomorphic system indicate additionally a sign of the local structural transition above the conventional structural phase transition temperature. This seems to be triggered by the ligand-deficient octahedral defects and can be explained in terms of the enhanced activity of the octahedral defects for the hindered rotation.     

Ergodic Properties of the Quantum Geodesic Flow on Tori

We study ergodic averages for a class of pseudodifferential operators on the flatN-dimensional torus with respect to the Schrödinger evolution. The later can be consider a quantization of the geodesic flow on . We prove that, up to semi-classically negligible corrections, such ergodic averages are translationally invariant operators.Mathematics Subject Classifications (2000) 58J50, 58J40, 81S10.     

Designing strategy to enhance mode selectivity of higher-output oxide-confined vertical-cavity surface-emitting lasers

Performance of modern oxide-confined (OC) vertical-cavity surface-emitting diode lasers (VCSEL s) is more sensitive to the construction details than in the case of other VCSEL s. In particular, a stable single-fundamental-mode operation is difficult to be achieved in these VCSEL s especially in higher-output large-size continuous-wave (cw) operating devices at higher temperatures. In the present paper, an operation of OC VCSEL s has been investigated with the aid of the comprehensive fully self-consistent model using the (GaIn)(NAs)/GaAs quantum-well VCSEL with two oxide apertures as a typical example. A new approach is proposed to enhance cw RT single-fundamental-mode low-threshold operation in higher-output OC VCSEL s. One of their oxide apertures should be shifted to the node position of the resonator standing wave where it is working as the electrical aperture only. Then diameters of both apertures may be changed independently giving an additional degree of freedom for VCSEL designing, which enables their optimisation. While the larger-diameter optical aperture placed in the anti-node position creates an efficient radial waveguiding effect, the smaller-diameter electrical aperture enhances a more uniform current injection into the VCSEL active region. Due to combining influence of both the apertures, the single-fundamental-mode operation is predicted in a large device with the 10-m-diameter active region even for 80 K active-region temperature increase over RT of the ambient. An impact of intentional detuning at room-temperature (RT) of VCSEL active-region gain spectrum towards shorter wavelengths with respect to the resonator mode improves mode selectivity is also analysed. PACS  42.55.Px; 02.60.Cb; 85.60.Bt     

Relaxation of excited states of Tm3+ and Tm3+-Eu3+ energy transfer in YVO4 crystal

Tm³⁺-Eu³⁺ energy transfer processes and relaxation dynamics of the ³ H ₄ and ³ F ₄ excited states of Tm³⁺ ions in 1 at. % Tm³⁺, 5 at. % Eu³⁺:YVO₄ single crystal were studied. Contribution of Tm³⁺-Eu³⁺ energy transfer reduces effectively the lifetime of terminal level in a potential ³ H ₄–³ F ₄ laser transition at around 1.48 μm. Adverse quenching of the ³ H ₄ emission by Eu³⁺ ions is found to be less efficient than that reported for Tm³⁺ + Tb³⁺ system in YVO₄. The classical Inokuti–Hirayama model accounts well for an experimental decay curve of the ³ H ₄ emission recorded for co-doped crystal. Stimulated emission cross section for ³ H ₄–³ F ₄ transition of Tm³⁺ at around 1.48 μm was analyzed taking into account the anisotropy of YVO₄ crystal. PACS 42.55.Xi; 42.62.Fi