Femtosecond laser pulses were focused on the interface of two glass specimens. Proper use of optical and laser processing parameters enables transmission welding. The morphology of the weld cross section was studied using differential interference contrast optical microscopy. In addition, a numerical model was developed to predict the absorption volumes of femtosecond laser pulses inside a transparent material. The model takes into account the temporal and spatial characteristics and propagation properties of the laser beam, and the transmission welding widths were subsequently compared with the absorption widths predicted by the model. The model can lead to the achievement of a desirable weld shape through understanding the effects of laser pulse energy and numerical aperture on the shape of the absorption volume. The changes in mechanical properties of the weld seams were studied through spatially resolved nanoindentation, and indentation fracture analysis was used to investigate the strength of the weld seams.
Hydrogenated amorphous silicon (a-Si:H) thin films have been considered for use in solar cell applications because of their significantly reduced cost. Their overall efficiency and stability, however, are less than that of their bulk crystalline counterparts. Limited work has been performed on solving the efficiency and stability issues of a-Si:H simultaneously. In this study, both surface texturing and crystallization on a-Si:H thin film are achieved through one-step femtosecond laser processing. The nanoscale conical and pillar-shaped spikes formed on the surface of a-Si:H films by femtosecond laser irradiation in both air and water are presented and enhanced light absorption is observed due to light trapping based on surface geometry changes, while the formation of a mixture of hydrogenated nanocrystalline silicon (nc-Si:H) and a-Si:H after crystallization suggests that the overall material stability can potentially be increased. The relationship among crystallinity, fluence, and scan speed is also discussed. Furthermore, a comparison of absorptance spectra for various surface morphologies is developed. Finally, the absorptance measurement across the solar spectrum shows that the combination of surface texturing and crystallization induced by femtosecond laser processing is very promising for a-Si:H thin film solar cell applications.
The influence of vasospasm on the permeability of the major cerebral arteries was studied using horseradish peroxidase (HRP). Experimental vasospasm was produced in canine basilar arteries by successive injections, 2 days apart, of autologous blood into the cisterna magna. HRP was injected intravenously or intracisternally 48 hours after the second injection of autologous blood, and all animals were killed by perfusion fixation 60 minutes after the injection of HRP. The distribution of HRP was observed by transmission electron microscopy. In 10 dogs injected intracisternally with HRP, 5 control dogs demonstrated a moderate amount of HRP in the intermuscular space through the adventitia. Five dogs with subarachnoid hemorrhages (SAHs) showed a moderate amount of HRP in the intermuscular space. In 11 dogs injected intravenously with HRP, 5 control dogs showed no leakage of HRP into vessel walls. Six dogs with SAHs showed HRP in the interendothelial space. These findings suggest that, despite SAHs, HRP seems to be able to circulate in the cerebrospinal fluid and makes contact with the cerebral vessels. This study suggests the possibility that spasmogenic substances may penetrate the vessel wall from the extraluminal side more easily than from the intraluminal side.
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