Synthesis and analysis of cupper nanoparticles produced by laser

Cupper nanoparticles are generated by using Nd:YAG laser nanosecond pulses using the liquid laser ablation technique. Nd:YAG of 6 and 10 nanoseconds pulse length with variable energy in the range are the two systems used (700-760 mJ ).The formation of cupper nanoparticles has been abolished using TEM with identical size distribution It has also been observed that when identical laser parameters are used, the average nanoparticles sizes of 80 and 120 nm for cupper are used.Furthermore, to approximate the temperature distributions for both cupper nanoparticles, the theoretical Mie-Gans model was used. Another factor that has been found is that the maximum temperature for gold nanoparticles is between (1000 K) and (1400 K), especially for the preparation of nanoparticles in the presence of 10 ns Nd:YAG.

Thermo-Fluid Design Simulation of Nd3+ POCl3 Transverse Flow Liquid Laser Cavity

CFD based thermal design of a transverse flow optical cavity is carried out for 1 kW Nd3+ POCl3 liquid laser source to investigate temperature and velocity distribution in the optical pumping region of the cavity. Temperature gradient and turbulence both affect the refractive index of the liquid gain medium, which results in optical path difference, divergence and hence, poorer quality of the laser beam. The main purpose of this design is to achieve uniform flow and least temperature gradient in the optical pumping region so that the optical path difference can be minimized and a good beam quality can be achieved. CFD model has been developed for carrying out thermo-fluid simulations for this thermal system and based on these simulations, an optimum geometry of inlet ports along with their position from optical pumping region have been proposed. A user defined function (UDF) is incorporated for the input of spatially varying heat source term in each cell of the optical pumping region of the cavity. Variations in refractive index and optical path difference are estimated from the temperature data using another UDF. Simulation reveals that mass flow rate between 1.5 kg/s to 2.0 kg/s maintains the optical homogeneity of gain medium. Preliminary experiments have been carried out to demonstrate the effect of flow rate on the beam divergence and thereby exhibiting the importance of present simulation work.

In-Liquid Laser Nanomachining by Photonic Nanojet in Laser Trapping System

Direct laser machining in sub-micron scale patterning at a surface of material remains a challenging task though the laser machining has been widely applied in various application. A photonic nanojet becomes a promising way to solve the problem by involving near-field focusing of light waves below the surface of a dielectric microsphere to fabricate pattern in micro- and nanometer size. By generating laser power to the microsphere and controlling the resulting photonic nanojet intensity distribution and position related to the workpiece, intended ablation size on the material could be controlled at the sub-micrometer scale. In this study, liquid is proposed as photonic nanojet machining medium due to several advantages that liquid offer during machining process. Laser trapping system is then introduced to the optical system to control the position of the microsphere during machining process. An in-liquid nanomachining by generating photonic nanojet in laser trapping configuration is a subject to study with the effect on the resulting ablation and viability of machining process from a set of parameters are investigated numerically using finite-difference time-domain (FDTD) technique. According to the findings of this study, nanometer scale, flexible, and fast novel laser nanomachining could be realized by combining photonic nanojet machining and laser trapping technique.

A One-Step Method for Fabrication of Wear-Resistant Amphiphobic Microdimple Arrays Using Under-Liquid Laser Machining

A one-step method using under-liquid laser machining (ULLM) is proposed for fabrication of microdimples on a cemented carbide surface with a wear-resistant amphiphobic property. The influence of laser processing parameters on the depth, width, and surface roughness (Ra) of the microstructures were investigated through single-factor experiments. On the basis of single-factor experiments, multiobjective optimization was carried out so that a desired surface morphology can be achieved. The model describing the relationships between laser processing parameters and corresponding responses was developed based on response surface methodology (RSM), and the adequacy of the model was assessed by analysis of variance (ANOVA) and verified experimentally. Subsequently, the desired microstructure arrays were then fabricated with the optimal processing parameters. Finally, the wear-resistant behaviors were comparatively studied for two kinds of amphiphobic surfaces by rubbing multiple times using 1000 grit metallographic sandpaper. The textured surface fabricated using the ULLM method exhibits excellent mechanical rubbing resistance as it maintains its amphiphobic character even after rubbing 300 m under the pressure of 2.4 MPa. This facile and low-cost method can be not only easily extended to other materials but also applied to fabricate amphiphobic surfaces with wear-resistance and self-healing properties.

Нелинейное оптическое поглощение в GaSe при лазерном возбуждении

: Nonlinear light absorption in GaSe crystals at high levels of optical excitation have been investiqated experimentally. Nd:YAG laser (1st, 2nd harmonic-1064 nm, 532 nm) and a liquid laser (radiation wavelength tuning range of 594-643 nm) were used as radiation sources. It is shown that the observed features in the absorption, luminescence, and photoconductivity spectra in the exciton resonance region in GaSe crystals at high levels of optical excitation can be explained by the interaction of excitons and the screening of the Coulomb interaction by free carriers.