The compositional variation of synthetic sodic amphiboles at high and ultra-high pressures

Sodic amphiboles in high pressure and ultra-high pressure (UHP) metamorphic rocks are complex solid solutions in the system Na 2 O–MgO–Al 2 O 3 –SiO 2 –H 2 O (NMASH) whose compositions vary with pressure and temperature. We conducted piston-cylinder experiments at 20–30 kbar and 700–800 °C to investigate the stability and compositional variations of sodic amphiboles, based on the reaction glaucophane=2jadeite+talc, by using the starting assemblage of natural glaucophane, talc and quartz, with synthetic jadeite. A close approach to equilibrium was achieved by performing compositional reversals, by evaluating compositional changes with time, and by suppressing the formation of Na-phyllosilicates. STEM observations show that the abundance of wide-chain structures in the synthetic amphiboles is low. An important feature of sodic amphibole in the NMASH system is that the assemblage jadeite–talc ± quartz does not fix its composition at glaucophane. This is because other amphibole species such as cummingtonite (Cm), nyböite (Nyb), Al–Na-cummingtonite (Al–Na-Cm) and sodium anthophyllite (Na-Anth) are also buffered via the model reactions: 3cummingtonite + 4quartz + 4H 2 O=7talc, nyböite + 3quartz=3jadeite + talc, 3Al–Na-cummingtonite + 11quartz + 2H 2 O=6jadeite + 5talc, and 3 sodium anthophyllite + 13quartz + 4H 2 O=3 jadeite + 7talc. We observed that at all pressures and temperatures investigated, the compositions of newly grown amphiboles deviate significantly from stoichiometric glaucophane due to varying substitutions of Al IV for Si, Mg on the M(4) site, and Na on the A-site. The deviation can be described chiefly by two compositional vectors: [Na A Al IV ][□ A Si] (edenite) toward nyböite, and [Na (M4) Al VI ][Mg (M4) Mg VI ] toward cummingtonite. The extent of nyböite and cummingtonite substitution increases with temperature and decreases with pressure in the experiments. Similar compositional variations occur in sodic amphiboles from UHP rocks. The experimentally calibrated compositional changes therefore may prove useful for thermobarometric applications.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42228/1/410-139-2-146_01390146.pd

Growth and low-threshold laser oscillation of an epitaxially grown Nd:YAG waveguide

We report 1064-µm laser operation of an epitaxially grown Nd:YAG planar waveguide with thresholds as low as ~0.7 mW when high-reflectivity mirrors are used. The output is single mode and, when a 83% reflectivity output coupler is used. has a diode pumped slope efficiency of ~40% Output powers in excess of 60 mW have been obtained when pumping with a Rhodamine 6G dye laser

Ion-implanted Nd:GGG channel waveguide laser

We report what is to our knowledge the first fabrication and laser operation of ion-implanted Nd:GGG channel waveguides. Diode-pumped operation has been achieved with absorbed power thresholds as low as ~2 mW and a slope efficiency of ~30% with respect to absorbed power

1-W quasi-cw near-diffraction-limited semiconductor laser pumped optically by a fibre-coupled diode bar

We describe a diode-bar-pumped vertical-external-cavity surface-emitting semiconductor laser, which in quasi-cw operation emitted a peak power of >1 W at 1020 nm in a circular, near diffraction-limited beam

Extended cavity surface-emitting semiconductor lasers

We review progress in the development of an unconventional type of semiconductor laser that has become the focus of much attention in recent years. The vertical-external-cavity surface-emitting laser is a diode-pumped solid-state laser with a semiconductor quantum well gain medium. It overcomes the limitation of conventional edge- and surface-emitting semiconductor lasers, which can offer either diffraction-limited beam quality, or high power, but not both in the same device. In this paper, we describe the physical principles of these lasers, emphasising those aspects that are unique to this hybrid. Optical characterisation of gain wafers is discussed, with particular attention to photoluminescence measurement; a powerful tool for the analysis of growth errors, the quantum efficiency of the active region, and the effect of multilayer interference effects on laser performance. Key achievements in the field to date, in high-power performance, ultrashort-pulse generation, and spectral coverage are summarised.<br/