Molecular-dynamics study of multi-pulsed ultrafast laser interaction with copper

Ultrafast laser has an undeniable advantage in laser processing due to its extremely small pulse width and high peak energy. While the interaction of ultrafast laser and solid materials is an extremely non-equilibrium process in which the material undergoes phase transformation and even ablation in an extremely short time range. This is the coupling of the thermos elastic effect caused by the pressure wave and the superheated melting of the material lattice. To further explore the mechanism of the action of ultrafast laser and metal materials, the two-temperature model coupling with molecular dynamics method was used to simulate the interaction of the copper and laser energy. Firstly, the interaction of single-pulsed laser and copper film was reproduced, and the calculated two-temperature curve and the visualized atomic snapshots were used to investigate the influence of laser parameters on the ablation result. Then, by changing the size of the atomic system, the curve of ablation depth as a function of laser fluence was obtained. In this paper, the interaction of multi-pulsed laser and copper was calculated. Two-temperature curve and temperature contour of copper film after the irradiation of double-pulsed and multi-pulsed laser were obtained. And the factors which can make a difference to the incubation effect were analyzed. By calculating the ablation depth under the action of multi-pulsed laser, the influence of the incubation effect on ablation results was further explored. Finally, a more accurate numerical model of laser machining metal is established and verified by an ultra-short laser processing experiment, which provides a new calculation method and theoretical basis for ultra-fast laser machining of air film holes in aviation turbine blades, and has certain practical guiding significance for laser machining.

Vector Optical Beam with Controllable Variation of Polarization during Propagation in Free Space: A Review

The vector optical beam with longitudinally varying polarization during propagation in free space has attracted significant attention in recent years. Compared with traditional vector optical beams with inhomogeneous distribution of polarization in the transverse plane, manipulating the longitudinal distribution of polarization provides a new dimension for the expansion of the applications of vector optical beams in volume laser machining, longitudinal detection, and in vivo micromanipulation. Two theoretical strategies for achieving this unique optical beam are presented in the way of constructing the longitudinally varying phase difference and amplitude difference. Relevant generation methods are reviewed which can be divided into the modulation of complex amplitude in real space and the filtering of the spatial spectrum. In addition, current problems and prospects for vector optical beams with longitudinally varying polarization are discussed.

Thermal Modelling for Laser Machining of SS316 L, Inconel 718 and Ti6Al4V

Laser beam machining is a complex thermal process of material removal. In this process, thermal energy is used to vaporize and remove the material from a particular area. Hence a comprehensive study is needed to completely understand the process which can be achieved by a simulation model and its validation through experimentation. In this paper this was achieved with an experimental study to see the relation between the Laser power and the material removal rate (MRR) of SS 316 L, Inconel 718 and Ti6Al4V during the process of Laser Machining. Also a 3D transient model of a moving Gaussian heat source was developed in ANSYS 18.2 to predict the MRR for different values of laser power. Mesh sensitivity analysis was done prior to the usage of the model so as to choose the perfect mesh size which can give the best results possible. After validation of the model, a close correlation was found between the experimental data and the simulation results. In the simulation model it was also observed that the temperature is maximum at the point of contact of the laser and is comparatively very high for a fraction of second.