Simple method for apodization of fibre Bragg gratings written by a Gaussian beam

Abstract

Computer simulation has been applied to the investigation of intergranular stress corrosion cracking in Ni-based alloys based on a hydrogen embrittlement mechanism. The simulation employs computational modules that address (a) transport and reactions of aqueous species giving rise to hydrogen generation at the liquid-metal interface, (b) solid-state transport of hydrogen via intergranular and transgranular diffusion pathways and (c) fracture due to the embrittlement of metallic bonds by hydrogen. A key focus of the development of the computational model has been the role of materials microstructure (precipitate particles and grain boundaries) on hydrogen transport and embrittlement. Simulation results reveal that intergranular fracture is enhanced as grain boundaries are weakened and that microstructures with grains elongated perpendicular to the stress axis are more susceptible to cracking. The presence of intergranular precipitates may be expected to either enhance or impede cracking, depending on the relative distribution of hydrogen between the grain boundaries and the precipitate-matrix interfaces. Calculations of hydrogen outgassing and ingassing demonstrate the strong effect of the charging method on the fracture behaviour.

Single-frequency Yb-doped fiber laser with distributed feedback based on a random FBG

“…Random FBGs were inscribed using the experimental setup shown in figure 1. It is based on a reliable phase-mask writing scheme [17]. During the inscription, a linear translator (6) with fiber (5) and phase mask ( 4) is moving at a constant speed across the beam of UV laser (1) focused by lens (2) into the fiber core.…”

“…We used software worked out in paper [20]. The simulation method for reflection spectra of regular FBG was described in detail in [17]. The programme was modified to calculate longitudinal intensity distribution inside the grating consisting of a number of subgratings with definite phases and amplitudes of the harmonic modulation.…”