R. Pohl

Toward 3D Printing of Pure Metals by Laser‐Induced Forward Transfer

3D printing of common metals is highly challenging because metals are generally solid at room conditions. Copper and gold pillars are manufactured with a resolution below 5 μm and a height up to 2 mm, using laser-induced forward transfer to create and eject liquid metal droplets. The solidified drops shape is crucial for 3D printing and is discussed as a function of the laser energy.

Imaging of the Ejection Process of Nanosecond Laser-induced forward Transfer of Gold

Laser-induced forward transfer is a direct-write process suitable for high precision 3D printing of several materials. However, the driving forces related to the ejection mechanism of the donor ma-terial are still under debate. To gain further insights into the ejection dynamics, this article presents results of a series of imaging experiments of the release process of nanosecond LIFT of a 200 nm thick gold donor layer. Images were obtained using a setup which consists of two dual-shutter cam-eras. Both cameras were combined with a 50× long-distance microscope and used to capture coaxial and side-view images of the ejection process. Bright field illumination of the scene was accom-plished by a 6 ns dual-cavity laser source. For laser fluence just above the transfer threshold of 140 mJ/cm2 , the formation of a jet and the subsequent release of a single droplet is observed. The drop-let diameter is estimated to be about 2 μm. For laser fluences above 400 mJ/cm2 the formation and rupture of a blistering bubble is observed, which ultimately leads to an undesirable ejection of mul-tiple droplets

Printing Functional 3D Microdevices by Laser-Induced Forward Transfer

Slender, out-of-plane metal microdevices are made in a new spatial domain, by using laser-induced forward transfer (LIFT) of metals. Here, a thermocouple with a thickness of 10 µm and a height of 250 µm, consisting of platinum and gold pillars is demonstrated. Multimaterial LIFT enables manufacturing in the micrometer to millimeter range, i.e., between lithography and other 3D printing technologies.

High-resolution imaging of ejection dynamics in laser-induced forward transfer

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.