Multi-kilowatt single-mode ytterbium-doped large-core fiber laser

We have demonstrated a highly efficient cladding-pumped ytterbium-doped fiber laser, generating >2.1 kW of continuous-wave output power at 1.1 µm with 74% slope efficiency with respect to launched pump power. The beam quality factor (M2) was better than 1.2. The maximum output power was only limited by available pump power, showing no evidence of roll-over even at the highest output power. We present data on how the beam quality depends on the fiber parameter, based on our current and past fiber laser developments. We also discuss the ultimate power-capability of our fiber in terms of thermal management, Raman nonlinear scattering, and material damage, and estimate it to 10 k

Automating Deductive Verification for Weak-Memory Programs

Writing correct programs for weak memory models such as the C11 memory model is challenging because of the weak consistency guarantees these models provide. The first program logics for the verification of such programs have recently been proposed, but their usage has been limited thus far to manual proofs. Automating proofs in these logics via first-order solvers is non-trivial, due to reasoning features such as higher-order assertions, modalities and rich permission resources. In this paper, we provide the first implementation of a weak memory program logic using existing deductive verification tools. We tackle three recent program logics: Relaxed Separation Logic and two forms of Fenced Separation Logic, and show how these can be encoded using the Viper verification infrastructure. In doing so, we illustrate several novel encoding techniques which could be employed for other logics. Our work is implemented, and has been evaluated on examples from existing papers as well as the Facebook open-source Folly library.Comment: Extended version of TACAS 2018 publicatio

No evidence of compensatory changes in energy balance, despite reductions in body weight and liver fat, during dapagliflozin treatment in type 2 diabetes mellitus: A randomized, double-blind, placebo-controlled, cross-over trial (ENERGIZE).

AimThis study assessed the impact of dapagliflozin on food intake, eating behaviour, energy expenditure, magnetic resonance imaging (MRI)-determined brain response to food cues and body composition in patients with type 2 diabetes mellitus (T2D).Materials and methodsPatients were given dapagliflozin 10 mg once daily in a randomized, double-blind, placebo-controlled trial with short-term (1 week) and long-term (12 weeks) cross-over periods. The primary outcome was the difference in test meal food intake between long-term dapagliflozin and placebo treatment. Secondary outcomes included short-term differences in test meal food intake, short- and long-term differences in appetite and eating rate, energy expenditure and functional MRI brain activity in relation to food images. We determined differences in glycated haemoglobin, weight, liver fat (by 1 H magnetic resonance spectroscopy) and subcutaneous/visceral adipose tissue volumes (by MRI).ResultsIn total, 52 patients (43% were women) were randomized; with the analysis of 49 patients: median age 58 years, weight 99.1 kg, body mass index 35 kg/m2 , glycated haemoglobin 49 mmol/mol. Dapagliflozin reduced glycated haemoglobin by 9.7 mmol/mol [95% confidence interval (CI) 3.91-16.27, p = .004], and body weight (-2.84 vs. -0.87 kg) versus placebo. There was no short- or long-term difference in test meal food intake between dapagliflozin and placebo [mean difference 5.7 g (95% CI -127.9 to 139.3, p = .933); 15.8 g (95% CI -147.7 to 116.1, p = .813), respectively] nor in the rate of eating, energy expenditure, appetite, or brain responses to food cues. Liver fat (median reduction -4.7 vs. 1.95%), but not subcutaneous/visceral adipose tissue, decreased significantly with 12 weeks of dapagliflozin.ConclusionsThe reduction in body weight and liver fat with dapagliflozin was not associated with compensatory adaptations in food intake or energy expenditure

Microstructuring and domain-engineering of lithium niobate using combinations of light, etching and poling

The work presented in this thesis reports methods for microstructuring of lithium niobate. The process of light induced frustrating etching, where light from a laser is used to inhibit the etching of iron doped lithium niobate, is the subject of a detailed investigation so a better understanding of the process can be developed. The process was found to be dependent upon illumination and etch times, iron dopant levels, and irradiance levels. Analysis of the structures formed revealed that they were resistant to the etchant used and were positively charged. Two dimensional Fourier transform analysis of images obtained were used to confirm that the structures preferentially propagated along 3 directions each 120º apart. A novel electro-optically controlled domain-engineered total internal reflection switch and beam deflector is also reported. Device construction uses electric field poling of lithium niobate to create two parallel but oppositely oriented domains. When an electric field is applied across the interface between these domains a change in the refractive index of equal magnitude but of opposite sign is induced. If light incident on this interface sees a sufficient difference in refractive index it can be total internally reflected. The total internal reflection switch shows high contrast ratio switching of greater than 20dB and is less wavelength dependent than other electro-optic switches, such as the Pockels cell. The beam deflector can produce large angular deflections, which are increased by faceting of the output face. Deflections of greater than 18o have been demonstrated using this technique. Cascading of devices and possible device implementations are also suggested

Latency effects and periodic structures in light-induced frustrated etching of Fe:doped LiNbO₃

Single crystals of z-cut 0.05% Fe:doped lithium niobate (Fe:LiNbO3), have been etched in a mixture of HF and HNO3 acids, under simultaneous illumination from a ~100 mW 488 nm wavelength Ar ion laser light source, focused to power densities of ~50 W cm–2 at the crystal surface exposed to the etchant. Etching is partially inhibited in illuminated regions, and the degree of inhibition shows a systematic latency: sites illuminated early in the etch run resist further etching even after the light is removed. Etched structures additionally exhibit regular periodic features of ~0.5 µm scale length. Details of these structures are shown, and the latent etching effect is discussed

Polarization-maintaining ytterbium-doped fibre with an aluminosilicate inner-cladding fabricated using in-situ doping technique

The ytterbium-doped fibre laser (YDFL) has become the forerunner for high-power fibre lasers and amplifiers largely owing to the broad emission of Yb3+ ions (lambda = 975 to 1200 nm) and their ability to be incorporated in a silica host in relatively high concentrations. Achieving multi-kilowatts of output power from a fibre has been made possible through improved fibre design and fabrication. In this paper we report on a robust polarization-maintaining (PM) YDFL with a unique aluminosilicate pedestal structure

Constraint Semantics for Abstract Read Permissions

The concept of controlling access to mutable shared data via permissions is at the heart of permission logics such as sep- aration logic and implicit dynamic frames, and is also used in type systems, for instance, to give a semantics to \read- only" annotations. Existing permission models have dier- ent strengths in terms of expressiveness. Fractional permis- sions, for example, enable unbounded (recursive) splitting, whereas counting permissions enable unbounded subtraction of the same permission amount. Combining these strengths in a single permission model appeared to increase the com- plexity for the user and tools. In this paper we extend our previous work on abstract read permissions by providing them with a novel constraint semantics, which retains the use of the domain of rational numbers but enables unboun- ded subtraction of identical amounts. Thus we can keep an intuitive model conducive to SMT solvers while enabling \counting.

Electro-optically controlled beam deflection for grazing incidence geometry on a domain-engineered interface in LiNbO₃

We report an analysis on the electro-optically induced beam deflection experienced by light traversing an interface between two anti-parallel domains in a sample of LiNbO3. In contrast to other work on prism deflection schemes, we present a grazing incidence geometry for light at incidence angles between 87.7° and 89.0° that has been investigated to maximise the deflection angles achievable. Further improvements can be obtained for both range of angular deflection and transmission uniformity, by faceting the exit face of the device at an optimum angle. We present a theoretical analysis for this configuration and compare with data obtained for a wavelength of 1.52 µm. A practical geometry would permit a deflection of ~140 mrad for an applied voltage of 1 kV

MCVD in-situ solution doping process for the fabrication of complex design large core rare-earth doped fibers

We report on the fabrication and characterization of rare-earth doped silica fibers manufactured using an in-situ solution doping technique, which is compatible with conventional modified chemical vapor deposition equipment. The in-situ technique permits significantly more doped layers to be deposited, compared to conventional solution doping, and is directly applicable for the fabrication of large core rare-earth doped fibers suitable for high-power fiber sources. Ytterbium-doped aluminosilicate fibers fabricated using the new in-situ doping technique are reported and the results are compared to fibers fabricated using a conventional solution doping method

Self-ordered sub-micron structures in Fe-doped LiNbO₃ formed by light-induced frustration of etching

We have produced millimetre-sized areas of self-ordered, sub-micron scale, complex structures in iron-doped single crystal lithium niobate, using the combined interaction of laser light and etching with acid. We report here the factors that influence the formation of the structures, and illustrate the types of structure that may be formed, using images taken by a scanning electron microscope (SEM) and subsequent Fourier Transform analysis of those images. We also consider the physical processes which initiate and control the growth of the structures