Abstract
The effects of the anisotropy orientation in hyperbolic media have only recently emerged as a way to control and manipulate several optical effects. Here, we show from both experimental and theoretical evidence that highly oriented-asymmetric absorption can be induced in simple crystal quartz. This can be achieved by controlling the orientation of the anisotropy with respect to the surface of the crystal at infrared regions where crystal quartz behaves as a hyperbolic medium. What is perhaps most intriguing here is that not only is the absorption asymmetric, but it can also be significantly enhanced. Finally, we also show various mechanisms through which the asymmetry in the absorption can be optimized, such as controlling the thickness of the crystal. Such phenomena are key for directional-dependent optical devices and present a pathway for engineering angle-encoded detection and sensing.
Highlights
Absorption is an intrinsic characteristic of optical materials, and in many cases, it is engineered to be as minimal as possible, especially for transmission-based devices [1,2]
High— and well-defined—absorption bands can be employed in a variety of devices including those used in sensing [3] and energy conversion [4]
In order to investigate the effect of the anisotropy orientation on the absorption bands of crystal quartz, we performed Fourier transform infrared spectroscopy measurements of the transmissivity tt and reflectivity rr using a Bruker Vertex 70 spectrometer
Summary
Absorption is an intrinsic characteristic of optical materials, and in many cases, it is engineered to be as minimal as possible, especially for transmission-based devices [1,2]. One interesting route to manipulating the behavior of absorption bands is to employ layered hyperbolic metamaterials These have been theoretically suggested as a way to achieve asymmetric transmission [9] and asymmetric guided waves. But still in the field of natural hyperbolic materials, anisotropic three-dimensional crystals—which are more readily available—have enabled researchers to mimic the optical control achieved in metamaterials. This is possible by engineering the direction of the crystal’s intrinsic anisotropy with respect to the crystal’s surface. We demonstrate experimentally and theoretically that controlling the direction of anisotropy in natural hyperbolic crystals offers a robust platform to engineer orientedasymmetric absorption, and to greatly enhance it. We performed far-infrared spectroscopy measurements as well as computer calculations using the example material crystal quartz
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