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Three-dimensional metallic microstructures find applications as stents in medicine, as ultrabroadband antennas in communications, in micromechanical parts or as structures of more fundamental interest in photonics like metamaterials. Direct metal printing of such structures using three-dimensional laser lithography is a promising approach, which is not extensively applied yet, as fabrication speed, surface quality, and stability of the resulting structures are limited so far. In order to identify the limiting factors, we investigate the influence of light-particle interactions and varying scan speed on heat generation and particle deposition in direct laser writing of silver. We introduce a theoretical model which captures diffusion of particles and heat as well as the fluid dynamics of the photo-resist. Chemical reactions are excluded from the model but particle production is calibrated using experimental data. We find that optical forces generally surmount those due to convection of the photo-resist. Simulations predict overheating of the photo-resist at laser powers similar to those found in experiments. The thermal sensitivity of the system is essentially determined by the largest particles present in the laser focus. Our results suggest that to improve particle deposition and to achieve higher writing speeds in metal direct laser writing, strong optical trapping of the emerging particles is desirable. Furthermore, precise control of the particle size reduces the risk of spontaneous overheating., Comment: Corrected formatting of metadata

Artificial gauge fields enable extending the control over dynamics of uncharged particles, by engineering the potential landscape such that the particles behave as if effective external fields are acting on them. Recent years have witnessed a growing interest in artificial gauge fields that are generated either by geometry or by time-dependent modulation, as they have been the enablers for topological phenomena and synthetic dimensions in many physical settings, e.g., photonics, cold atoms and acoustic waves. Here, we formulate and experimentally demonstrate the generalized laws of refraction and reflection from an interface between two regions with different artificial gauge fields. We use the symmetries in the system to obtain the generalized Snell law for such a gauge interface, and solve for reflection and transmission. We identify total internal reflection (TIR) and complete transmission, and demonstrate the concept in experiments. Additionally, we calculate the artificial magnetic flux at the interface of two regions with different artificial gauge, and present a method to concatenate several gauge interfaces. As an example, we propose a scheme to make a gauge imaging system - a device that is able to reconstruct (image) the shape of an arbitrary wavepacket launched at a certain position to a predesigned location., Comment: 23 p