###### Abstract  
The potential to deposit minute amounts of material from a donor to an acceptor substrate at precise locations makes laser-induced forward transfer (LIFT) a frequently used tool within different research fields, such as materials science and biotechnology. While many different types of LIFT exist, each specialized LIFT application is based on a different underlying transfer mechanism, which affects the to-be-transferred materials in different ways. Thus, a characterization of these mechanisms is necessary to understand their limitations. The most common investigative methods are high-speed imaging and numerical modeling. However, neither of these can, to date, quantify the material deposition. Here, analytical solutions are derived for the contact-based material deposition by LIFT, which are based on a previously observed equilibrium state. Moreover, an analytical solution for the previously unrecognized ejection-based material deposition is proposed, which is detectable by introducing a distance between the donor and acceptor substrates. This secondary mechanism is particularly relevant in large scale production, since each deposition from a donor substrate potentially induces a local distance between the donor and acceptor substrates. transfer mechanisms; fluorescence imaging; vertical scanning interferometry +
Footnote †: journal:  
0000-0001-7880-3888-2222-22222-  
contaminates the transferred material. To avoid such contamination, sacrificial polymer layers were introduced. Two of the most common approaches are evaporation and ejection of triazene polymer (TP) [20] and blister-actuated (BA) [21] LIFT, which is based on the thermal polyimide expansion. On the one hand, the customizable absorption spectrum of the triazene polymer and potential to transfer solid and liquid materials through TP LIFT make it a versatile tool for the generation of polymer sensors [22] and organic light emitting diodes [23]. However, TP LIFT is an ablation-based process [24; 25]. Thus, the ablation can still harm extremely delicate materials, and the irradiated donor substrate location can only be used once. On the other hand, only liquid materials can be transferred through the BA LIFT, and the thick isolating polyimide layer has usually a set absorption spectrum. Nevertheless, the isolating polyimide effectively mitigates the interaction between the laser and to-be-transferred material, which enables the manufacturing of light-emitting diodes and biosensors [26; 27]. Since the material deposition is based on a contact between the acceptor substrate and a blister-induced directional jet of the donor substrate [28], the irradiated location is reusable. In 2016, the combinatorial LIFT (cLIFT) [29] was introduced for parallel and on-demand chemical synthesis [30]. Within this process, a thick reusable polyimide layer is used as a sacrificial layer, and a polymer coating embedded with chemical building blocks is used as the donor substrate. We previously showed that the material deposition through cLIFT is mainly driven by the expansion of the sacrificial polyimide layer during laser irradiation and can be divided into four steps (Figure 1): (a) minor deformation of the polyimide after initial laser irradiation; (b) bell-shaped expansion of the polyimide in normal direction of the surface at a given time with a continuously decreasing expansion rate; (c) established stable contact with the acceptor due to the expanded polyimide with no further polyimide expansion; (d) relaxation of the polyimide layer and donor substrate material deposition after finished laser irradiation. Despite some similarities with the BA LIFT, the material deposition mainly occurs through a direct contact between the donor and acceptor substrates, which is established by the expansion of the polyimide layer [31]. Yet, a ring structure appears with a large distance (distance \(>\) polyimide expansion) between the donor and acceptor substrates [31], which indicates an additional ejection-based material deposition, radially to the expanding surface.