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Research Papers

The Interactions of Microhole Sidewall With Plasma induced by Femtosecond Laser Ablation in High-Aspect-Ratio Microholes

[+] Author and Article Information
Benxin Wu1

Department of Mechanical, Materials and Aerospace Engineering, Illinois Institute of Technology, Chicago, IL 60616bwu11@iit.edu

Sha Tao

Department of Mechanical, Materials and Aerospace Engineering, Illinois Institute of Technology, Chicago, IL 60616

Shuting Lei

Department of Industrial and Manufacturing Systems Engineering,  Kansas State University, Manhattan, KS 66506

1

Corresponding author.

J. Manuf. Sci. Eng 134(1), 011007 (Jan 12, 2012) (5 pages) doi:10.1115/1.4005431 History: Received January 17, 2011; Revised September 30, 2011; Published January 12, 2012; Online January 12, 2012

High-aspect-ratio microholes have many important applications, but their drilling is very challenging. Femtosecond (fs) laser ablation provides a potential solution, but involves many complicated physical processes that have not been well understood, which have hindered its practical application. One of these is that the plasma induced by laser ablation at the hole bottom will transfer some of its energy to the hole sidewall as it expands in the microhole. The plasma–sidewall interaction has been rarely studied in literature, and it is still not clear if or not the energy transferred from the plasma is sufficient to cause significant material removal from the sidewall. Direct time-resolved observations are extremely difficult due to the small temporal/spatial scales and the spatial constraint inside the hole, while the sidewall characterization after laser ablation is difficult to distinguish between the possible material removal due to plasma energy transfer and that due to direct laser energy absorption by the sidewall. In this paper, a physics-based model is applied as the investigation tool to study the plasma–sidewall interaction in fs laser drilling of high-aspect-ratio microholes. It has been found that for the studied conditions the energy transferred from the plasma is not sufficient to cause significant material removal from the sidewall through any thermally induced phase change process.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 1

Schematic of the model calculation procedure (a), and the plasma–sidewall interaction (b) (the hole bottom is at z = 0, and the hole central axis is at r = 0; plasma expansion in z direction is approximately assumed to be 1D with the same diameter as the hole; teq is the electron-lattice equilibrium time)

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Figure 2

The contour plots for the hole sidewall temperature at t = 100 and 390 ps (hole radius is 50 μm, laser pulse has a duration of 170 fs and a fluence of 10 J/cm2 ; a schematic showing the plasma height from the hole bottom is also given, where the color does not represent the plasma temperature; due to the small heat affected zone, only a small, 0.5 -μm thick sidewall domain is shown)

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Figure 3

The hole sidewall surface temperature variation with z at different delay times (the hole and laser parameters are the same as Fig. 2; the hole bottom is at z = 0, and the sidewall surface is at r = 50 μm)

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Figure 4

The temperature distribution of the hole sidewall along the r direction at z = 10 μm and t = 390 ps (hole radius is 50 μm, and hence, the hole sidewall surface is located at r = 50 μm; the hole and laser parameters are the same as Fig. 2)

Grahic Jump Location
Figure 5

The hole sidewall surface temperature variation with z at different delay times (the hole and laser parameters are the same as Fig. 2 except the hole radius is 10 μm; the hole bottom is at z = 0 and the sidewall surface is at r = 10 μm)

Grahic Jump Location
Figure 6

The temperature distribution of the hole sidewall along the r direction at z = 10 μm and t = 390 ps (hole radius is 10 μm, and hence, the hole sidewall surface is located at r = 10 μm; the hole and laser parameters are the same as Fig. 5)

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