High-repetition-rate, high-average-power, diode-pumped 2.94-microm Er:YAG laser

We have demonstrated more than 3 W of average output power from a 2.94-mu;m quasi-cw diode-pumped total internal reflection (TIR) Er:YAG laser operating at 100 Hz with a 4% duty cycle. Moreover, repetition rates of up to 600 Hz at more than 1.2-W output power have been achieved. The cavity consists of a plane-mirror resonator of 40-mm length and uses three of five TIR regions within the laser crystal as pump facets to efficiently couple the pump energy into the resonant laser mode. Differential efficiencies of up to 18.3% have been achieved at an optimum pump pulse width in the range of 300 micros .     

Electronic structure of Zn in oxide spinels

Using⁶⁷Zn Mössbauer absorption and emission spectroscopy, we have investigated the electronic structure at the A and B sites in the normal spinels (Zn)[Al₂]O₄, (Zn)[Fe₂]O₄ and (Zn)[Ga₂]O₄. Within each system, the center shift S_c at the A site is more positive. In all systems investigated, the electric field gradientV _u at the B site is negative. The values for S_C andV _U scale with oxygen nearest-neighbour distance to Zn. In the Fe spinel, a transferred magnetic hyperfine field is observed at the Zn site below the antiferromagnetic ordering temperatureT _N=10 K. For a more detailed discussion of the chemical bond, we have performed ab initio Hartree-Fock cluster calculations for the Al and Fe spinels. Our experimental and theoretical results show that all hyperfine parameters are essentially determined by covalency effects. Our data on the Ga spinel raise the question of a partially inverse structure.     

High-resolution67Zn-Mössbauer study of oxide spinels

We report on first experiments to investigate the electronic structure in the normal spinels ZnAl₂O₄ and ZnFe₂O₄ and in the inverse spinels Zn₂SnO₄ and Zn₂TiO₄ using the high-resolution⁶⁷Zn-Mössbauer spectroscopy. The electric field gradient for⁶⁷Zn at the B (octahedral) site in ZnAl₂O₄ is negative, whereas the A (tetrahedral) site remains essentially cubic, however, with a more positive center shift. ZnFe₂O₄ orders antiferromagnetically at ≈10K. Due to superexchange a magnetic field is observed at⁶⁷Zn. In the inverse spinels short range order leads to only few (Zn,Sn) and (Zn,Ti) configurations at the octahedral sites. The s-electron densities at the⁶⁷Zn sites are distinct and cover a surprisingly broad range for Zn₂TiO₄. This strongly suggests that d-electrons of Ti play an essential role in the chemical bond of this compound.     

Nuclear levels in228Th populated in the decay of228Pa

The electron-capture decay of²²⁸Pa to levels in²²⁸Th has been studied using mass-separated sources and high-resolutionγ-ray and conversion-electron spectroscopy. A level at 979.5 keV is assigned as 2⁺ member of a second excited K_π=0⁺ band, with the 0⁺ band head at 938.6 keV. The 2⁺ and 3⁺ members of a second excited K_π=2⁺ band at 1153.5 and 1200.5 keV, which decay by strongE0 transitions to the 969 keVγ-vibrational band, are confirmed. In addition we tentatively propose a K_π=1⁺ band at 944 keV. The K_π=0^?, 1^? and 2^? members of the octupole quadruplet are confirmed, and theγ decay of these levels is analysed in an approach, in which the mixing of the octupole bands by the Coriolis interaction is taken into account. It is suggested that octupole correlations might be important for theE1 transition moments. A total of 29 levels is observed between ～1.4 and ～2.0 MeV, for which the nuclear structure, and the possible assignment to rotational bands, is unclear.     

High-spin two-quasiparticle bands in76Br

Excited states of the doubly-odd nucleus V6Br have been studied with in-beam γ-ray spectroscopy techniques. In addition to the positive parity band that has been extended up to I=(13) a I^π=4^? isomer (T_1/2=0.5±0.2 ns) and two bands of negative parity have been identified. The bands are discussed in terms of two-quasiparticle configurations. For the band built on the 4_? isomer the configuration πg9/2?νf5/2 or p3/2 is proposed.