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Research Papers

# Transient Analysis of Laser Ablation Process With Plasma Shielding: One-Dimensional Model Using Finite Volume Method

[+] Author and Article Information
Deepak Marla

Ph.D. Student
e-mail: deepakmarla@iitb.ac.in

Upendra V. Bhandarkar

Associate Professor
e-mail: bhandarkar@iitb.ac.in

Suhas S. Joshi

Professor
e-mail: ssjoshi@iitb.ac.in
Department of Mechanical Engineering,
Indian Institute of Technology Bombay,
Mumbai, India 400076

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF Micro AND Nano-Manufacturing. Manuscript received February 10, 2012; final manuscript received December 8, 2012; published online March 22, 2013. Assoc. Editor: Don A. Lucca.

J. Micro Nano-Manuf 1(1), 011007 (Mar 22, 2013) (9 pages) Paper No: JMNM-12-1014; doi: 10.1115/1.4023287 History: Received February 10, 2012; Revised December 08, 2012

## Abstract

This paper presents a comprehensive transient model of various phenomena that occur during laser ablation of TiC target at subnanosecond time-steps. The model is a 1D numerical simulation using finite volume method (FVM) on a target that is divided into subnanometric layers. The phenomena considered in the model include: plasma initiation, uniform plasma expansion, plasma shielding of incoming radiation, and temperature dependent material properties. It is observed that, during the target heating, phase transformations of any layer occur within a few picoseconds, which is significantly lower than the time taken for it to reach boiling point ($~ns$). The instantaneous width of the phase transformation zones is observed to be negligibly small ($<5nm$). In addition, the width of the melt zone remains constant once ablation begins. The melt width decreases with an increase in fluence and increases with an increase in pulse duration. On the contrary, the trend in the ablation depth is exactly opposite. The plasma absorbs about 25–50% of the incoming laser radiation at high fluences ($20-40 J/cm2$), and less than 5% in the range of $5-10 J/cm2$. The simulated results of ablation depth on TiC are in good agreement at lower fluences. At moderate laser fluences ($10-25 J/cm2$), the discrepancy of the error increases to nearly ±7%. Under prediction of ablation depth by 15% at high fluences of $40 J/cm2$ suggests the possibility of involvement of other mechanisms of removal such as melt expulsion and phase explosion at very high fluences.

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## Figures

Fig. 1

Schematic of ablation process with plasma shielding effect

Fig. 2

Schematic showing the evaluation of plasma height

Fig. 3

Laser intensity profile with time

Fig. 4

Schematic showing the different stages of the target during the laser heating process. Where S, L, and V represent solid, liquid, and vapor, respectively.

Fig. 5

Transient temperature profiles of different layers along the depth for a pulse time of 10 ns (FWHM) and fluence of (a) 4 J/cm2, (b) 10 J/cm2, (c) 15 J/cm2, and (d) 20 J/cm2, where “i” represents the layer number

Fig. 6

Temperature variation along the depth for a pulse time of 10 ns (FWHM) and a fluence of (a) 4 J/cm2, (b) 10 J/cm2, (c) 15 J/cm2, and (d) 20 J/cm2

Fig. 7

Plot of ablation and melt depth for a fluence of 10 J/cm2

Fig. 8

Plot of ablation depth versus time for different fluences

Fig. 9

Plot of melt depth versus time for different fluences

Fig. 10

Plot of ablation depth as a function of time for different pulse times and fluence of 20 J/cm2

Fig. 11

Plot of melt width as a function of time for different pulse times and fluence of 20 J/cm2

Fig. 12

A comparison of laser intensities before and after plasma shielding for a fluence of (a) 5 J/cm2, (b) 10 J/cm2, (c) 20 J/cm2, and (d) 40 J/cm2

Fig. 13

Laser energy absorbed by plasma with time at different fluences

Fig. 14

Percentage of energy absorbed by plasma for different laser fluences

Fig. 15

Comparison of numerical results with the experimental results of Oliveira et al. [20]

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