Single-crystal sapphire fibers have been grown with the laser-heated pedestal-growth method with losses as low as 0.3 dB /m at 2.94 ?m. With the incorporation of a computer-controlled feedback system, fibers have been grown with less than +/-0.5 % diameter variation, or +/-1.5 ?m for a 300- ?m fiber. The losses in these fibers have been reduced further through a postgrowth anneal at 1000 degrees C in air, from 5.4 to 1.5 dB /m at 543 nm and from 0.4 -0.3 dB /m at 2.94 ?m. These fibers delivered 4.7 W at 10 Hz of Er:YAG laser power.

Optical properties of single-crystal sapphire fibers

Catalytic hydrogenation is one of the backbones of the chemical industry. Controlling the reaction behaviour of the activated hydrogen species over oxide-supported metal catalysts is essential. Aside from the expected addition to substrates, the activated hydrogen species would also destroy the active structures. Here we show that, with the assistance of alkali cations, the atomically dispersed Ru(iii) on Al2O3 exhibits enhanced performance in the hydrogenation of a broad range of substrates. The alkali cations facilitate the hydrogenation mediated by heterolytic hydrogen species, which not only restrain the hydride species from migrating to interfacial oxygen, thus suppressing the reduction and aggregation of ruthenium, but also stabilize the negatively charged transition states and intermediates through enhanced Columbic attraction. Distinctively, an inverse H/D isotope effect related to H2 splitting as the rate-determining step over the atomically dispersed ruthenium-catalysed hydrogenation is predicted and confirmed. Alkali metals have been traditionally used to promote heterogeneous catalysts, albeit their mode of action remains controversial. Now, the authors demonstrate the multifaceted role of sodium ions in promoting atomically dispersed Ru(iii) on Al2O3, resulting in a superior hydrogenation catalyst.

Alkali ions secure hydrides for catalytic hydrogenation

Sapphire single‐crystal fibers with diameters of 110 μm and lengths of over 2 m have been grown by the laser‐heated pedestal growth method. The fibers are free of imperfections such as voids and bubbles. The minimum loss of 0.5 dB/m was measured in the near infrared at 1064 nm. Absorption loss at 2936 nm was 0.88 dB/m with a damage threshold higher than 1.2 kJ/cm2 for 110‐μs‐long pulses making tissue ablation feasible with fibers several meters in length.

Characterization of single‐crystal sapphire fibers for optical power delivery systems

This article reviews the spectroscopic properties of hydrogen bound to a large variety of synthetic compounds like simple oxides, perovskites, the LiNbO3 family, KTP, sillenites, eulytites, borates, garnets, spinels and some others. In almost all compounds the OH stretch mode is found in the range 3200-3700 cm−1, with isotope replica of deuterium (2350-2750 cm−1) and a few examples of tritium (2050-2250 cm−1). The fundamental vibration, the isotope replica and the corresponding overtones are described with an anharmonic oscillator model. A nonlinear relation between the anharmonicity and the harmonic frequency is found and interpreted using recent second order perturbation calculations. An often pronounced temperature dependence of the stretch mode and phonon coupling is discussed. Data for the stretching vibration influenced by additional weak or strong doping are presented. Atomistic defect models are described and tested by means of light polarization, external perturbations like pressure and electric ...

OH- ions in oxide crystals

Current development of the research of radiation damage in ionic solids is reviewed. Emphasis is placed on the correlation between elementary radiation damage processes and the atomic and electronic structures of the materials. Both the radiation damage induced by electronic excitation and by elastic collision are treated. For the former two crucial processes, the self-trapping of excitons and the formation of stable Frenkel pairs from the self-trapped excitons in several materials, is discussed in terms of the structures of materials. Deficiency in the available data on the knock-on threshold energies are pointed out. Available information of Frenkel pairs produced by electronic and elastic encounters is surveyed. Possible models of defect clustering are summarized and existing information on clustering is discussed on their basis.

T.J. Turner

Papers

V centers in single crystal Al2O3