Light transmission through obstacles without a direct line of sight
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Light propagation is typically hindered by obstacles along its path. A common strategy is therefore to shape the light field so that it avoids interacting with them, an idea recently popularized by invisibility cloaks. Previous studies have shown that transmission can be achieved either by steering light around localized objects or, when apertures are present, by guiding it through them-both mechanisms being well described by ray optics. Here, we show that a specific class of obstacles with no direct line of sight can nonetheless transmit light. Experimentally, we demonstrate a transmission of 27% through a set of three masks lacking any direct line of sight, enabled by proper wavefront engineering using a microlens array. This effect, based on a reinterpretation of the Talbot effect, is captured by the generalized eikonal equation. Our results provide a striking counterexample to the long-standing ray-optics picture that light propagates in straight lines in homogeneous media.
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