We report on the achievement of continuous wave bi-frequency operation in a membrane external-cavity surface-emitting laser (MECSEL), which is optically pumped with up to 4 W of 808 nm pump light. The presence of spatially specific loss of the intra-cavity high reflectivity mirror allows loss to be controlled on certain transverse cavity modes. The regions of spatially specific loss are defined through the removal of Bragg layers from the surface of the cavity high reflectivity mirror in the form of crosshair patterns with undamaged central regions, which are created using a laser ablation system incorporating a digital micromirror device (DMD). By aligning the laser cavity mode with the geometric centre of the loss patterns, the laser simultaneously operated on two Hermite-Gaussian spatial modes: the fundamental HG00 and the higher order HG11 mode. We demonstrate bi-frequency operation over a range of pump powers and sizes of spatial loss features, with a wavelength separation of approximately 5 nm centred at 1005 nm.
No abstract
The process of drilling of toughened carbon fiber composite materials presents numerous problems during structural assembly. The extremely abrasive nature of carbon fibers along with the softer resin quickly dull sharp tools, split, tear, pullout, and push-in the fibers on the hole boundaries. The presence and growth of such flaws seriously impairs the structural stability, durability, and reliability particularly under fatigue loading. This research aims to investigate the failure modes, pattern, and sequence of damage mechanisms in toughened carbon-epoxy composite in relation to the drilling dynamics. The surface morphology of the damaged fibers in the sectioned holes was examined by scanning electron microscopy (SEM). The drill forces were determined by drill dynamometer to investigate the drilling thrust and torque. The photoelastic stress analysis was used to determine the strains around hole of the lowest ply. The most critical failure mode was found to be shear crimping of −45° fibers due to microbuckling. This resulted in formation of damage pits that were spaced apart periodically at an angle of 45° on hole boundaries. The through-the-thickness drilling forces caused delamination in the resin rich region of −45°/90° interlayer. The SEM, dynamometer, and photoelastic strain results were correlated to predict the onset of failure modes. The results have been explained in the light of analytical models based on fracture mechanics. Measures have been suggested for minimizing the damage on carbon-epoxy composite hole boundaries.
Highly porous nanofoam can be fabricated via multiphoton ablation of a material by raster-scanning femtosecond laser pulses over the material surface. Here, we show the fabrication of nanofoam on the inside surface of a hollow silica capillary that has an inner and outer diameter of 640 and 700 µm respectively. A thin layer of nanofoam was fabricated over ~70% of the inner surface of the capillary. Ray-tracing simulations were used to determine the positional corrections required to account for refraction on the curved surface and also to explain the inability to fabricate nanofoam on the side walls of the capillary.
Canadian Petroleum Ltd. and partners in the Yemen Masila Block have successfully used detailed three-dimensional reservoir modeling and reservoir simulation to optimize the development of the larger oilfields in the Masila area. The models were used to predict reservoir performance and plan additional development drilling which subsequently demonstrated that the models accurately predicted drilling results. The main producing horizon in the Masila area is the Cretaceous Upper Qishn formation, a clastic-dominated transgressive depositional sequence with fluvial sediments at the base, tidal dominated estuarine sediments in the middle, and marine shoals at the top. This variable array of facies presents modeling challenges but the resulting heterogeneous models provide a realistic representation of actual reservoir characteristics. This paper describes the approach used to stochastically distribute both facies bodies and petrophysical parameters, and to upscale the model for reservoir simulation, while preserving the complex reservoir description. The Tawila field was the first Masila field to have wells drilled on the basis of the modeling effort, with very encouraging results. For these new well locations, the model successfully predicted both reservoir development and oil- water contact movements resulting from production from existing wells. This paper presents key conclusions and predictions from the modeling and reservoir simulation, and compares them to the results from subsequent drilling. As a result of the successful development drilling, these models are now an integral part of reservoir management and development planning for all Masila fields. P. 715
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