![]() In the presence of a different GF on either side of the interface, the trajectories of waves crossing from one side to the other are governed by the symmetries in the system, which are expected to result in an effective Snell’s law, whereas the reflection and transmission coefficients arise from the specific boundary. Such a gauge edge was employed to demonstrate analogies to the Rashba effect 25, optical waveguiding 26, 27, topological edge states 28, 29 and back-refraction 30. In these systems, both sides of the interface have the same basic dispersion properties, altered only by applying a different GF on each side. With the growing interest in topological systems 22, which necessitate GFs 23, 24, it was suggested that the interface between two regions of the same medium but with different GFs in each region can create an effective edge. These artificial GFs are generated either by the geometry 17 or by time-dependent modulation 18 of system parameters. With the advent of the particle-wave duality, artificial GFs have been demonstrated to act on photons 16, 17, 18, 19, cold atoms 20, 21, acoustic waves, etc. Artificial GFs are a technique for engineering the potential landscape such that neutral particles will mimic the dynamics of charged particles driven by external fields. Gauge fields (GFs) are a basic concept in physics describing forces applied on charged particles. Generally, such a “gauge interface” marks a different dispersion curve on either side of the interface hence, it must affect the transmission and reflection at the interface. However, an interface can also separate two optical systems that differ only by the artificial gauge fields created in them. These can be two materials with different permittivities or two different periodic systems (photonic crystals) composed of the same material, e.g., an interface between two dissimilar waveguide arrays 15. Traditionally, the Fresnel equations describe the reflection and transmission of electromagnetic waves at an interface separating two media with different optical properties. The behavior of waves in the presence of an interface can exhibit fundamental features, e.g., total internal reflection (TIR), back-refraction for negative-positive refraction index interfaces 4, 5, and even confinement of states to the interface itself, such as Tamm and Shockley states 6, 7, plasmon polaritons 8, 9, Dyakonov states 10, 11 and topological edge states 12, 13, 14. By cascading several such systems, each with its own optical properties, it is possible to design complex structures that give rise to various important devices and systems, such as lenses, waveguides 1, resonators, photonic crystals 2, and even localization phenomena, when random interfaces are involved 3. Snell’s law and the Fresnel coefficients are the cornerstones of describing the evolution of electromagnetic waves at an interface between two different media. As an example, we propose a scheme to make a gauge imaging system-a device that can reconstruct (image) the shape of an arbitrary wavepacket launched from a certain position to a predesigned location. In addition, we calculate the artificial magnetic flux at the interface of two regions with different artificial gauge fields and present a method to concatenate several gauge interfaces. We identify total internal reflection (TIR) and complete transmission and demonstrate the concept in experiments. We use the symmetries in the system to obtain the generalized Snell law for such a gauge interface and solve for reflection and transmission. Here, we formulate and experimentally demonstrate the generalized laws of refraction and reflection at an interface between two regions with different artificial gauge fields. Recent years have witnessed a growing interest in artificial gauge fields generated either by the geometry or by time-dependent modulation, as they have been enablers of topological phenomena and synthetic dimensions in many physical settings, e.g., photonics, cold atoms, and acoustic waves. ![]() Artificial gauge fields the control over the dynamics of uncharged particles by engineering the potential landscape such that the particles behave as if effective external fields are acting on them.
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