Sharif Digital Repository

The optimum condition for the reactive gas-assisted Nd:YAG laser cuttings is described in this article. The cut kerf width is investigated for a laser power range of 50-170 W and a gas pressure of 1-6 bar for steel and mild steel materials. Variation of sample thickness, material type, gas pressure and the laser power on the cut width and slot quality are considered in this study. An overall 338 experiments at different experimental conditions are performed and the kerf results are compared. Optimum conditions for the steel and mild steel materials with a thickness range of 1-2 mm are obtained. The optimum condition for the steel cutting results in a minimum kerf width of 0.2 mm at a laser... 

This research aims to investigate the effect of pulsed Nd:YAG laser micro-welding on the microstructure, texture and magnetic properties of ultra-thin Fe-Co-7.15 wt% V magnetic alloy. Optical microscopy, scanning electron microscopy and electron backscattered diffraction techniques were used to study the microstructural evolutions. Also, vibrating sample magnetometry was used to characterize the magnetic properties. The results showed that the fractions of low Σ coincidence site lattice boundaries in the fusion zone are higher than those of the base metal. The welded samples experience a significant decrease in their magnetic properties. It was found that the formation of new fiber texture... 

Laser ablation is a novel non-mechanical wheel preparation method for optimizing the treatment costs of superabrasive tools. In this study the thermal effects of picosecond laser radiation on CBN superabrasive grinding wheel surface is analytically and experimentally investigated. The analytical approach is intended to find threshold process parameters for selective ablation of cutting grains and bond material. It has been analytically and experimentally shown that, the extent of material degradation is defined by the maximum surface temperature induced by the laser radiation which is in turn defined by the laser beam energy. It is also suggested that, the depth of laser thermal effects is... 

Machining of ceramics often involves many challenges due to their high hardness, brittleness, and low thermal properties. Laser assisted machining (LAM) is a promising technology for improving the machinability of hard-to-cut materials. In this work, laser assisted machining of slip cast fused silica (SCFS) ceramics is investigated by presenting a numerical thermal analysis of laser effects on material behaviour. A transient three-dimensional heat transfer analysis for laser assisted turning of SCFS is performed using finite element method. Temperature distributions in SCFS cylindrical specimens are obtained. Experimental results are provided to validate the numerical results  

This study aimed to investigate the changes in crystalline structure and resistance to demineralization of human dental surface enamel treated with erbium-doped yttrium aluminium garnet laser (Er:YAG) laser and fluoride. The enamel surfaces were divided into four groups according to the treatment process including, (L): irradiated with Er:YAG; (F): treated with acidulated phosphate fluoride gel (LF): Pre-irradiated surfaces with Er:YAG subjected to acidulated phosphate fluoride gel and (FL): laser irradiation was performed on the fluoridated enamel surface. Before and after the treatment procedure, the samples were evaluated using X-ray diffraction, scanning electron microscope (SEM) and the... 

Conversion of CH4 molecule into higher hydrocarbons using two different wavelengths of 248 nm KrF laser and 355 nm of third harmonic of Nd:YAG laser is studied experimentally and theoretically. The stable products are analyzed and the effect of pressure on conversion of methane is measured. The detected reaction products are C2H2, C2H4, and C2H6. The conversion efficiency of 33.5% for 355 nm in comparison to 2.2% conversion for 248 nm for C2H2 is achieved. The potential of laser parameters as an important variable in controlling of final products is investigated  

12 mJ, 10-Hz green pulses from frequency doubled Nd:YAG laser was used for pumping Rhodamine 6G in a dye laser based on multiple-prism beam expander. In order to increase the stability of the output pulse, a unique dye cell with variable dimensions of active medium was designed and constructed. By using multiple-prism dispersion theory, conditions for zero-dispersion in two and four-prism beam expander configuration was calculated. In the case of two-prism configuration, tuning range of dye laser was 565–595 nm and the linewidth of pulse at 580 nm was about 1.8 nm and it is in good agreement with the calculated amount of 1.6 nm. Furthermore, using four-prism configuration tuning range of... 

Tunability of the Fermi level of graphene is exploited to implement a plasmonic nano-color-sorter for scanning near-field optical microscope (SNOM) applications capable of handling large tip sample couplings. Nano-color-sorting has been used in SNOM through creating multiple spatially separated hot spots for different incident wavelengths. We show that in the presence of high-refractive-index samples an unwanted redshift in the spectral response of the dual-color probe occurs. This limitation can be compensated for using graphene and adjusting its chemical potential to obtain a blueshift in probe spectral response. The Method of Moments analysis technique is employed to engineer the probe... 

Nd:YAG laser treatment was used in order to increase surface cell adhesion aspects of polycarbonate (PC) films prepared via melt process. The treatment was carried out under different wavelengths and beam diameters. ATR-FTIR and UV spectra obtained from different samples before and after laser treatment in air showed that laser irradiation has induced some chemical and physical changes in surface properties. The irradiated films were also characterized using scanning electron microscopy (SEM) and contact angle measurements. Effect of pulse numbers on the surface properties was also investigated. Cell culture test was used to evaluate cell adhesion property on the PC films before and after... 

A wide variety of carbon nanostructures were generated by a Q-switched Nd : YAG laser (1064 nm) while mostly nanodiamonds were created by an ArF excimer laser (193 nm) in deionized water. They were characterized by transmission electron microscopy, Raman spectroscopy and x-ray photoelectron spectroscopy. It was found that the IR laser affected the morphology and structure of the nanostructures due to the higher inverse bremsstrahlung absorption rate within the plasma plume with respect to the UV laser. Moreover, laser-induced breakdown spectroscopy was carried out so that the plasma created by the IR laser was more energetic than that generated by the UV laser  

Tungsten oxide nanoparticles were fabricated by a pulsed laser ablation method in deionized water using the first harmonic of a Nd:YAG laser (λ = 1064 nm) at three different laser pulse energies (E1 = 160, E2 = 370 and E3 = 500 mJ/pulse), respectively. The aim is to investigate the effect of laser pulse energy on the size distribution and gasochromic property of colloidal nanoparticles. The products were characterized by dynamic light scattering (DLS), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and UV-Vis spectroscopy. The results indicated that WO 3 nanoparticles were formed. After ablation, a 0.2 g/l PdCl 2 solution was added to activate the solution against... 

The present paper reports the effects of Nd:YAG laser welding on the microstructure, phase transformation, cyclic deformation behavior, and corrosion resistance of Ti-55 wt.% Ni wire. The results showed that the laser welding altered the microstructure of the weld metal which mainly composed of columnar dendrites grown epitaxially from the fusion line. DSC results indicated that the onset of the transformation temperatures of the weld metal differed from that of the base metal. Cyclic stress-strain behavior of laser-welded NiTi wire was comparable to the as-received material; while a little reduction in the pseudo-elastic property was noted. The weld metal exhibited higher corrosion... 

Direct solvent exfoliation of bulk MoS2 with the assistance of poly(3-hexylthiophene) (P3HT) produces a novel two-dimensional organic/inorganic semiconductor hetero-junction. The obtained P3HT-MoS2 nanohybrid exhibits unexpected optical limiting properties in contrast to the saturated absorption behavior of both P3HT and MoS2, showing potential in future photoelectric applications  

In this study, colloidal tungsten oxide nanoparticles were fabricated by pulsed laser ablation of tungsten target using the first harmonic of a Nd:YAG laser (1064 nm) in deionized water. After ablation, a 0.33 g/lit HAuCl4 aqueous solution was added into as-prepared colloidal nanoparticles. In this process, Au3+ ions were reduced to decorate gold metallic state (Au0) onto colloidal tungsten oxide nanoparticles surface. The morphology and chemical composition of the synthesized nanoparticles were studied by AFM, XRD, TEM and XPS techniques. UV-Vis analysis reveals a distinct absorption peak at ∼530 nm. This peak can be attributed to the surface plasmon resonance (SPR) of Au and confirms...