"Computational study of laser ablation of Aluminium with shielding effect" by Alex Povitsky

Seminar by Alex Povitsky, Professor, Department of Mechanical Engineering, The University of Akron, US

Abstract

Computational study is peformed to better understand the nanosecond-scale laser ablation of aluminum for a wide range of laser ablated plume characteristics. Aluminum is one of the most widely used materials in industry today and a better understanding of how to best manipulate this material is important. When a laser interacts with its target, a plume consisting of gaseous target material, solid particles and droplets, and plasma is generated that limits the efficiency of successive laser pulses. This process is known as shielding of laser pulses by ablated multi-phase plumes. The implementation of shielding due to plasma generation in the ejected plume material was developed and combined with shielding due to particles. The amount of laser energy to reach the target is obtained as a function of properties of previously ejected plumes.

Using conservation of mass, momentum, and energy to predict the dynamics of plumes for subsequent laser pulses, the shielding process is successfully implemented into the ANSYS/Fluent. The results of the present model are validated by comparison with published experimental [1] and computational [2] data. Plasma shielding is significant because of high temperatures in the ablated plumes. The high temperature zones were located along the axis of the incident laser and did not extend across the entire laser radius. Therefore, plasma shielding was more impactful closer to the target center than along the edges while particle shielding was relatively more uniform across the target. The decrease in mass ejected from the first to second pulse was significant compared to later pulses. In several instances, results show that the ejected mass per pulse converged to a certain value. The ejected mass does not continually decrease for later pulses as the plume has more time to disperse. In the future the developed model can be used for ablation of other metals such as boron, nickel, copper, and titanium.

References [1] Auerhammer, J. M. et al. Dynamic Behavior of… Appl. Phys. B, v. 68, n. 1, p. 111, 1999. [2] J. Appl. Phys. 100, 024911 (2006); https://doi.org/10.1063/1.2217108 [3] Deepak Marla et al 2014 J. Phys. D: Appl. Phys. 47 105306