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Research Papers

Modeling of Ultrafast Phase Change Processes in a Thin Metal Film Irradiated by Femtosecond Laser Pulse Trains

[+] Author and Article Information
Jing Huang, J. K. Chen

Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, MO 65211

Yuwen Zhang1

Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, MO 65211zhangyu@missouri.edu

Mo Yang

College of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China

1

Corresponding author.

J. Heat Transfer 133(3), 031003 (Nov 15, 2010) (8 pages) doi:10.1115/1.4002444 History: Received April 13, 2009; Revised November 25, 2009; Published November 15, 2010; Online November 15, 2010

Ultrashort laser pulses can be generated in the form of a pulse train. In this paper, the ultrafast phase change processes of a 1μm free-standing gold film irradiated by femtosecond laser pulse trains are simulated numerically. A two-temperature model coupled with interface tracking method is developed to describe the ultrafast melting, vaporization, and resolidification processes. To deal with the large span in time scale, variable time steps are adopted. A laser pulse train consists of several pulse bursts with a repetition rate of 0.5–1 MHz. Each pulse burst contains 3–10 pulses with an interval of 50 ps–10 ns. The simulation results show that with such configuration, to achieve the same melting depth, the maximum temperature in the film decreases significantly in comparison to that of a single pulse. Although the total energy depositing on the film will be lifted, more energy will be transferred into the deeper part, instead of accumulating in the subsurface layer. This leads to lower temperature and temperature gradient, which is favorable in laser sintering and laser machining.

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Figures

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Figure 6

The relationship between melting depth and maximum temperature; comparison between single pulse and pulse train

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Figure 7

The effects of repetition rate

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Figure 8

The effects of pulse number per train

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Figure 9

The effects of separation time between single pulses

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Figure 10

The effects of heat loss at surface

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Figure 5

The effects of single pulse fluence on the irradiation process

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Figure 4

The evolution of melting caused by a typical laser pulse train

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Figure 3

The surface lattice temperature caused by a typical laser pulse train

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Figure 2

Laser pulse train

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Figure 1

Laser irradiation on thin film

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