טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentDon-Yehiya Gilad
SubjectInvestigation of Particles Plume Generated by Laser Ablation
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Josef Stricker
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Laser pulse focused on a solid or liquid surface, can remove material from its surface by vaporization and particle splashing. This process is called laser ablation. Laser ablation is used for many applications, such as semiconductors manufacturing, micromachining, satellite propulsion, chemical analysis etc.

This work presents a numerical simulation for laser ablation process. The simulation is divided into two stages where the first stage is used to generate the initial condition to the second stage. The first stage is a one dimensional model that describes the first few tens of nanoseconds, during laser operation, and includes several physical phenomena among those are:

  1. Heating and vaporization of the brass target by the laser irradiance.
  2. Expansion of the vapor in one dimension with nitrogen ambient gas at one atmosphere.
  3. Plasma formation and laser absorption in the plasma.

The simulation in the first stage is based on a model which has been presented in the literature.

The second stage simulates the process at later times where the assumption of one dimensional expansion is not valid. The simulation calculates several physical phenomena, among those are: 

  1. Expansion of the plume in three dimensions.
  2. Particle dynamics in the plume.
  3. Particle vaporization.

The influence of the ambient gas pressure on the flow field, and on the particles behavior was investigated. The effects of particles initial velocity on their dynamics were studied as well.

At the beginning of the simulation, the particles were placed in five rows above the target. During the simulation, particle diameter decreases with increasing initial distance from the target and from the axis of symmetry.

Higher initial velocity led to decrease in particles diameter due to higher temperature in their path and therefore higher vaporization.

Increasing ambient gas pressure, cause to slower plume expansion and higher vapor temperature. As a result there was higher vaporization from the particles. 

Finally, estimation for condensed particles location was made. Particles are most likely to be form in high vapor concentration. Maximum vapor concentration found close to the target in the vortex zone. Part of the flow moves to the target, and pushes the vapor and the particles away from the symmetry axis.

There is a resemblance between copper vapor distribution in the case of 2 atmosphere ambient pressure, to copper particles distribution in experiment results shown in the literature.