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 material 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 cameras. 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 accomplished 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 droplet 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 multiple droplets.