Concentration dependence of the fluorescence decay profile in transition metal doped chalcogenide glass

In this paper we present the fluorescence decay profiles of vanadium and titanium doped gallium lanthanum sulphide (GLS) glass at various doping concentrations between 0.01 and 1% (molar). We demonstrate that below a critical doping concentration the fluorescence decay profile can be fitted with the stretched exponential function: exp[-(t/τ)β], where τ is the fluorescence lifetime and β is the stretch factor. At low concentrations the lifetime for vanadium and titanium doped GLS was 30µs and 67µs respectively. We validate the use of the stretched exponential model and discuss the possible microscopic phenomenon it arises from. We also demonstrate that above a critical doping concentration of around 0.1% (molar) the fluorescence decay profile can be fitted with the double exponential function: a*exp-(t/τ1)+ b*exp-(t/τ2), where τ1 and τ2 are characteristic fast and slow components of the fluorescence decay profile, for vanadium the fast and slow components are 5µs and 30µs respectively and for titanium they are 15µs and 67µs respectively. We also show that the fluorescence lifetime of vanadium and titanium at low concentrations in the oxide rich host; gallium lanthanum oxy-sulphide (GLSO) is 43µs and 97µs respectively, which is longer than that in GLS. From this we deduce that vanadium and titanium fluorescing ions preferentially substitute into high efficiency oxide sites until at a critical concentration they become saturated and low efficiency sulphide sites start to be filled

Emission from a bismuth doped chalcogenide glass spanning from 1µm to 2.7µm

We report emission from a bismuth doped chalcogenide glass with a full width half maximum of 850 nm. The quantum efficiency and lifetime were 32% and 175 µs. We report two new bismuth emission bands at 2000 and 2600 nm

Eden Valley observation boreholes : hydrogeological framework and groundwater level time series analysis

This report summarises the analysis of groundwater level data from 26 boreholes in the Eden Valley, Cumbria. By undertaking a statistical analysis on 18 of these boreholes greater insight into the hydrogeology has been obtained. The work is presented to build a foundation on which greater analysis can be undertaken

Tension over equitable allocation of water : estimating renewable groundwater resources beneath the West Bank and Israel

Competition for water resources between Palestine and Israel is an ongoing cause of tension. The Western Aquifer Basin forms a major part of the complex, largely karst, limestone system of the West Bank Mountain Aquifer. The aquifer crops out and is recharged solely in the semi-arid uplands of the West Bank and groundwater flows west beneath Israel to discharge at the Yarqon and Nahal Taninim springs near the Mediterranean coast. Annual recharge to the aquifer is not easy to quantify but lies within the range 270×106 to 455×106 m3 a−1, and current uncertainties do not support definition of a single value of long-term average recharge. The resource is heavily exploited and abstraction is directly controlled and apportioned between Israel and the West Bank by Israel. The key to equitable apportionment is the determination of the long-term average recharge to the basin, which also requires definition of the eastern boundary of the basin to confirm the recharge area. Calculations include empirical formulae and process-based models that are likely to constrain the best estimate provided that there is appropriate, ongoing monitoring. Improved understanding can then be fed back into the model

Outcomes of a chemistry content professional learning session: Teachers' perspectives

The national curriculum for chemistry includes topics that have not previously been taught at secondary level. In response to requests for teacher professional learning (PL) covering these topics, a course called 'Divide and Analyse' was developed. Investigations into the PL needs of chemistry teachers were carried out in conjunction with the pilot session. Pre- and post-PL survey responses and focus group discussions provided a wealth of information about the needs of chemistry teachers and how university chemists can support them. Three themes of support for chemistry teaching were identified: resources for chemistry teaching, content PL for chemistry teachers and enrichment excursions/incursions for school students. Teachers explained that this type of support may contribute to making the study of chemistry more interesting and relevant for their students. A partnership between chemistry teachers and university chemists can facilitate the provision of the identified support for chemistry teaching. It was concluded that a community of practice partnership had developed from the Divide and Analyse PL. A model that brings together the major findings of the study is proposed

Coupled cavity modelocking of a Nd:YAG laser using second harmonic generation

Recently it has been demonstrated that intracavity second harmonic generation (SHG) In a Nd:YAG laser can lead to mode locking with pulse durations of ~ 100 ps at 532 nm. Other work has shown that nonlinear processes in an external coupled cavity can effectively mode lock a laser. These two mechanisms are combined to mode lock a Nd:YAG laser using SHG as the nonlinearity

Single-photon stored-light Ramsey interferometry using Rydberg polaritons

We demonstrate a single-photon stored-light interferometer, where a photon is stored in a laser-cooled atomic ensemble in the form of a Rydberg polariton with a spatial extent of 10×1×1µm3. The photon is subject to a Ramsey sequence, i.e., “split” into a superposition of two paths. After a delay of up to 450 ns, the two paths are recombined to give an output dependent on their relative phase. The superposition time of 450 ns is equivalent to a free-space propagation distance of 135 m. We show that the interferometer fringes are sensitive to external fields and suggest that stored-light interferometry could be useful for localized sensing applications

Second harmonic generation and birefringence of some ternary pnictide semiconductors

A first-principles study of the birefringence and the frequency dependent second harmonic generation (SHG) coefficients of the ternary pnictide semiconductors with formula ABC$_2$ (A = Zn, Cd; B = Si, Ge; C = As, P) with the chalcopyrite structures was carried out. We show that a simple empirical observation that a smaller value of the gap is correlated with larger value of SHG is qualitatively true. However, simple inverse power scaling laws between gaps and SHG were not found. Instead, the real value of the nonlinear response is a result of a very delicate balance between different intraband and interband terms.Comment: 13 pages, 12 figure

Well-posedness of boundary layer equations for time-dependent flow of non-Newtonian fluids

We consider the flow of an upper convected Maxwell fluid in the limit of high Weissenberg and Reynolds number. In this limit, the no-slip condition cannot be imposed on the solutions. We derive equations for the resulting boundary layer and prove the well-posedness of these equations. A transformation to Lagrangian coordinates is crucial in the argument