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. So far, most of the experimental studies of nanosecond LIFT, are based on post process analysis of either the donor layer and/or the deposits, which were transferred to the receiving substrate. 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, the formation of a jet and the subsequent release of a single droplet was observed. The droplet diameter was esti-mated to be about 2 μm. Analysis of the coaxial images indicates the emission of a spectral broad range light which was identified as thermal radiation.