6 March 2014 High-resolution imaging of ejection dynamics in laser-induced forward transfer
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Laser-induced Forward Transfer (LIFT) is a 3D direct-write method suitable for precision printing of various materials. As the ejection mechanism of picosecond LIFT has not been visualized in detail, the governing physics are not fully understood yet. Therefore, this article presents an experimental imaging study on the ejection process of gold-based LIFT. The LIFT experiments were performed using a 6.7 picosecond Yb:YAG laser source equipped with a SHG. The beam was focused onto a 200 nm thick gold donor layer. The high magnification images were obtained using bright field illumination by a 6 ns pulsed Nd:YAG laser source and a 50× long-distance microscope objective that was combined with a 200 mm tube lens. For laser fluence levels up to two times the donor-transfer-threshold, the ejection of a single droplet was observed. The typical droplet radius was estimated to be less than 3 μm. A transition of ejection features towards higher fluence, indicates a second fluence-regime in the ejection process. For higher laser fluence, the formation of an elongated gold jet was observed. This jet fragments into multiple relatively small droplets, resulting in a spray of particles on the receiving substrate.
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R. Pohl, R. Pohl, C. W. Visser, C. W. Visser, G. R. B. E. Römer, G. R. B. E. Römer, C. Sun, C. Sun, A. J. Huis in 't Veld, A. J. Huis in 't Veld, D. Lohse, D. Lohse, "High-resolution imaging of ejection dynamics in laser-induced forward transfer", Proc. SPIE 8967, Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XIX, 89670X (6 March 2014); doi: 10.1117/12.2037231; https://doi.org/10.1117/12.2037231

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