Papers by Keyword: Pulsed Laser

Abstract: The effect of laser energy number of pulses on the compositional, morphological, topographic, and optical properties of selenium oxide nanoparticles SeO2 nanoparticles prepared by pulsed laser ablation of selenium in a target liquid immersed in water with Nd:YAG laser pulses with energy 400 mJ was investigated using a different number of laser pulses 250 and 300. X-ray diffraction (XRD) tests revealed that the SeO2 nanoparticles exhibited a hexagonal crystal structure. Scanning electron microscope (SEM) tests revealed that the form and size of the produced SeO2 NPs are dependent on the number of laser pulses. The dispersion of nanoparticles was proportional to the increase in laser energy generated by the number of pulses. AFM investigations revealed extremely distributed ball-shaped SeO2 particles. The optical energy gap of SeO2 nanoparticles generated was evaluated using optical characteristics and found to be 3.37 to 4.3 eV for SeO2 induced by 250 and 300 pulses, respectively. The biological effectiveness results revealed that employing laser energy with a pulse number of 300P resulted in the greatest inhibition.

Abstract: The welding of shape-memory alloys is a challenge due to the fact that there are numerous compositions and because the properties are greatly influenced by the temperature. Of the multitude of shape-memory alloy systems, the most popular and widely used is the Ni-Ti system. Pulsed laser welding is a solution used for joining NiTi shape-memory alloys, having the advantage of localized heating and the possibility to adjust the welding parameters to obtain optimal properties. NiTi wires were welded using a 500W pulsed laser equipment by varying the current intensity. Thus, laser melted spots were made on a NiTi wire, changing only the value of current intensity in 20A increments in the range of 100-200A. The results analyzed by scanning electron microscopy showed, as expected, that as the current intensity increased, the spot size and the heat affected zone (HAZ) increased for each spot. Differential scanning calorimetry revealed that the martensitic transformation is still present in all samples, but with a decrease in peaks related to the phase transformation, as well as an increase of the temperature (8-12 °C), compared to the base material.

Abstract: CdS thin films have been grown on glass substrate at 250^o C employing pulsed laser deposition method. The effect of laser pulses number on the crystalline structure, surface morphology, optical properties, and films thickness have been studied. XRD analysis shows that the CdS films have polycrystalline and hexagonal nanostructure with three notable peaks along (100), (002), and (101) planes and preferentially orientated along (101). The crystallite size of the preferred orientation was in the range of (21.4 - 27.3 nm). With small pulses number, XRD pattern confirms the formation of CdO with three peaks (111), (200), and (220). Theses peaks gradually reduce with the increasing of the pulses. The absorbance of the films is in the visible part of the spectrum. The band gap of the synthesized films reduces by rising the number of laser pulses. AFM studies indicate that the grain size and surface roughness increase with the film thickness. Due to the good crystalline structure and optical properties of the film of the highest thickness, it has been grown on a wafer silicon substrate for solar cell applications measurements. Hall measurements indicate low resistivity of 0.3×10-2 (Ω.m) and high conductivity of 3.3×10+2 (Ω.m)-1. The efficiency of the n-CdS/ p-Si junction has been calculated to be 3.4 % using I-V characteristic measurement. Keywords: pulsed laser, thin films, structural, optical, morphology, solar cell measurements

Abstract: To investigate the cutting quality of Carbon Fibre Reinforced Polymer (CFRP) with pulsed laser, experiments of high modulus CFRP were carried out using a Nd: YAG pulsed laser with wavelength of 1064nm. Experiments with five factors and five levels were designed to apply the response surface methodologies (RSM). The influence rule of processing parameters consisting scanning speed, pulse frequency, pulse energy, pulse duration and gas pressure on the morphology of machining region including the kerf width, kerf taper and the width of heat affected zone were studied, and the interactions of these input parameters on cutting qualities were also analyzed. Parameters optimization were conducted based on the mathematical model using the optimization software Design Expert. Verification experiments were carried out to prove the adequacy of the optimization results. The infrared laser with pulsed mode was found to be an effective method in processing high modulus CFRP.

Abstract: This paper reports an experimental study of laser welding on duplex stainless steel UNS S32205 employed in the oil and natural gas industries. A pulsed Nd:YAG laser was used to weld the specimens. Bead on plate condition was used. Scanning Electron and Optical microscopy was applied to measure and analyze the cross-sectional of the weld bead. From the experimental results, it was found that the shape and size of the welded spot depend not only on the laser energy, but also on the pulse duration and the focus position. Metallographic observations showed that the microstructure of the weld metal was characterized by large ferrite grains with intra and inter-granular austenite. Large voids delimited by the molten zone boundary were observed in weld beads with low pulse duration. The heat affected zone resulting from the welding is pretty much absent and no cracks were detected.

Abstract: Precision grinding is one of the important processes for finishing of hardened steel parts. However, the grinding process might be quite costly providing the parts with shape complexity should be finished because a number of production steps are needed. Also, this process has some environmental issues, such as disposal of a large amount of grinding sludge and grinding fluid. Precision cutting would become a better alternative process to reduce cost and environmental burden because process steps can be simplified by use of CNC machine tools with PcBN cutting insert if deterioration of cutting tool edge by wear and chipping can be suppressed for long duration. In this study, to improve performance of a PcBN cutting insert, such as wear resistance and defect resistance by the applying of pulse laser processing to sharpen cutting edge in order to realize substitution of cutting for grinding. Precision cutting experiments for hardened steel are conducted by use of the PcBN insert with sharp and tough edges processed by pulsed laser and, for comparison, by use of the PcBN insert ground with diamond wheel. From the results of cutting experiments, it was found that precision cutting with PcBN insert processed by pulsed laser can provide a steady cutting state for a long cutting duration, and a smooth finished surface comparable to precision grindings.

Abstract: We make ​​a preliminary analysis of the process during pulsed laser damages CCD from the aspect of detector’s thermal effect by it.We build simulation model of CCD irradiated by laser.The simulation results show that silica damage energy density threshold range between 1-5.8 J/cm². This magnitude doesn’t appear to be much different from previous data. So it shows that simulation results are believable.

Abstract: The promising processing techniques of micro scale parts are very important in products miniaturization and functions enhancement. Combination of two or more processing techniques gives better processing performance especially when dealing with difficult-to-cut materials. For that reason, the combination of laser beam and micro milling process has been widely studied and proven efficient in reducing cutting force and tool life extension. However, this process needs a precise temperature control in order to eliminate heat effect generated by laser beam irradiation. In this study, temperature distributions are determined numerically to characterize the melted zone and heat affected zone geometry. From the results, the estimation of tool and micro milling cutter distance together with the allowable depth of cut are determined.

Abstract: Laser can stimulate sound wave, its possible for fiber laser to evoke neural activity safely and produce the auditory perception, this acts as the electrode role in cochlear implant. Moreover, the laser is characterized by definite direction and optical signal between adjacent fibers dont readily interfere. Therefore, optical fiber cochlear implant based on optoacoustic effect is promising. The design and preparation of an experimental system based on optoacoustic effect is introduced in this paper. The selection of laser source and the control methods of optical signal were discussed, and testing results of the fiber optoacoustic effect, including the time domain waveforms and spectrograms of the evoked optoacoustic sound were given. Also, a preliminary discussion for the extended fiber array system applied in artificial fiber cochlea as an alternative to electrodes stimulation was progressed.

Abstract: Being widely used in aircrafts structure and aircraft turbine parts, chemical processing equipment and marine hardware, titanium alloys are well known of their high strength and corrosion resistant even though this material is categorized as hard to machine material and reactive to hydrogen and oxygen in elevated temperature. And joining titanium alloys in fabricating parts used in aerospace and medical application requires excellent temperature distribution control to minimize the heat effect. Due to this, laser welding is one of the best methods for the selective area heat induction capability and high accuracy. However, proper processing parameter need to be determined based on the characteristics of the laser source and processed material. Hence, this study is carried out to clarify the performance of a medium range powered laser by comparing and analyzing the welding beads characteristics changes occurred under different processing parameters. Welding beads were analyzed visually from two directions to obtain overall view of molten zones.