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Analysis of geometrical characteristics of holes drilled in alumina ceramic using solid state Nd:YaG laser and quasi-continuous-wave ytterbium fiber laser
Řiháková, L. ; Chmelíčková, Hana
Technical ceramic such as Al2O3 can be found in many fields of human activity due to its characteristic properties, like high hardness and brittleness, high thermal conductivity and wear, and chemical resistance. In this paper the percussion drilling of alumina ceramics was performed by Nd:YAG laser and quasi-continuous-wave ytterbium fiber laser with the aim to produce holes with high quality. Both processes were compared and the effects of the laser parameters on the holes quality and geometry were examined. Namely, the effects of wavelength, pulse energy, pulse length and number of pulses on the entrance and exit holes diameter and circularity, taper, aspect ratio and the presence of the melt were analyzed. The optimum parameters were found for both lasers ensuring the production of high duality holes without cracks or impurities. The holes were observed by scanning confocal microscope OLYMPUS LEXT 3100.
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Properties of hybrid LasTIG welds of of S460MC steel
Šebestová, Hana ; Horník, Petr ; Mrňa, Libor
Modern structural high strength low alloy steels achieve their excellent strength properties through the microalloying and carefully controlled process of hot rolling. Welding technologies with low heat input are advisable to maintain fine-grained structure of these steels and to minimize heat distortions. Laser beam is a source of highly concentrated energy and thus very narrow heat affected zone is reached during laser welding. Unfortunately, undesirable quenching microstructures can be generated thanks to high heating and cooling rates in both weld metal and heat affected zone. Their amount can be reduced through the temperature rate decrease realized using preheating. Technology of LasTIG hybrid welding combines laser welding with the preheating by an electric arc. The contribution evaluates the effect of electric current on LasTIG weld macro and microstructure and microhardness.
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Laser standard for precise length and time metrology
Pravdová, Lenka ; Hrabina, Jan ; Čížek, Martin ; Číp, Ondřej
We present the development and the achieved parameters of the telecom C-band optical frequency laser standard. Compact and robust laser system based on ultra-narrow linewidth fiber laser achieves relative frequency stabilities from 9e-13/1s down to 8e-14/256s levels and can serve as stable frequency source for applications of dissipation of precise time and frequency, wavelength calibrations in optical telecommunication or laser interferometry measurement systems.
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Interferometrical system for bulge test thin film characterization
Pikálek, Tomáš ; Holzer, Jakub ; Tinoco, H.A. ; Buchta, Zdeněk ; Lazar, Josef ; Chlupová, Alice ; Náhlík, Luboš ; Sobota, Jaroslav ; Fořt, Tomáš ; Kruml, Tomáš
Behavior of thin film materials undergoing stress and deformation differs from bulk materials. A common method for the mechanical characterization of thin films is nanoindentation based on indenting a small tip into the material. A different approach is a bulge test technique. In this method, a differential pressure is applied on a free-standing membrane and the mechanical properties (Young’s modulus and residual stress) are calculated from the shape of the bulged membrane. In our experiments, we developed an interferometrical system for the membrane shape measurement during the bulge test.
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Advanced laser welding methods
Mrňa, Libor ; Horník, Petr ; Šebestová, Hana
Recently, modern methods of laser welding have been developed. Laser welding methods employing scanning techniques are used. The basis of scanner laser welding is a laser head including system of two computer-controlled deflecting mirrors, supplemented with special optics, allowing fast beam movement over a given area. The second method using deflecting mirrors is wobbling welding. In this method, besides the main movement, laser beam oscillates along the welding trajectory. Weld seam width and microstructure can be varied by controlling of parameters of beam micro-motion.\nAnother advanced method is hybrid laser-TIG welding where arc discharge can serve as a heat source regulating heating or cooling rate. This method can be used for high strength fine-grained steels welding, where the additional heat affects the weld microstructure and the heat affected area and consequently improves mechanical properties of the weld joint.\n
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Deterministic Aperiodic Image Device
Horáček, Miroslav ; Meluzín, Petr ; Krátký, Stanislav ; Knápek, Alexandr ; Mika, Filip ; Chlumská, Jana ; Matějka, František ; Král, Stanislav ; Brunn, Ondřej ; Giričová, D. ; Kopal, Jaroslav ; Kolařík, Vladimír
The paper deals with the analysis, design and preparation of a diffractive optically variable imaging device consisting of a deterministic aperiodic mesh formed by basic optical elements. The theoretical basis is complemented by numerical analysis and presentation of the implemented master and its replicas.
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Experimental fluorescence device for dielectrophoretic sorting of droplets in microfluidic chips
Ježek, Jan ; Pilát, Zdeněk ; Šmatlo, Filip ; Zemánek, Pavel
At present, many chemical and biological disciplines use different forms of spectroscopy for their observations. One of the most common methods is fluorescence spectroscopy. During the last seven years, microfluidic techniques began developing rapidly, using channels in which two immiscible liquids create droplets with diameters from units to tens to hundreds of micrometers. These droplets serve as liquid microcontainers containing the analysed sample and the necessary reagents. Using special microfluidic techniques, it is possible to fuse droplets with different contents (controlled triggering of chemical reactions), to change the concentration of reactants in the droplet with high speed (concentration gradients), or sort the droplets by content (creation of new cell strains).\n\n
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