Abstract
The development of innovative terahertz (THz) imaging systems has recently moved in the focus of scientific efforts due to the ability to screen substances through textiles or plastics. The invention of THz imaging systems with high spatial resolution is of increasing interest for applications in the realms of quality control, spectroscopy in dusty environment and security inspections. To realize compact THz imaging systems with high spatial resolution it is necessary to develop lenses of minimized thickness that still allow one to focus THz radiation to small spot diameters with low optical aberrations. In addition, it would be desirable if the lenses offered adaptive control of their optical properties to optimize the performance of the imaging systems in the context of different applications. Here we present the design, fabrication and the measurement of the optical properties of spectrally broadband metamaterial-based gradient index (GRIN) lenses that allow one to focus THz radiation to a spot diameter of approximately one wavelength. Due to the subwavelength thickness and the high focusing strength the presented GRIN lenses are an important step towards compact THz imaging systems with high spatial resolution. Furthermore, the results open the path to a new class of adaptive THz optics by extension of the concept to tunable metamaterials.
Highlights
The progress of the terahertz(THz) technology is currently suffering from a lack of adequate optical components, such as waveplates, lenses, beam splitters etc. that on the other hand belong to standard optical components in other frequency ranges
Free-standing metamaterial membranes do enable the integration in very compact THz systems and possess the potential to open up novel ways to realize a new class of adaptive THz optics that can be controlled by optical and/or electrical means [2, 3]
It can be seen that the gradient index (GRIN) lens strongly focused the incident THz radiation to a spot size in the order of one wavelength
Summary
The progress of the terahertz(THz) technology is currently suffering from a lack of adequate optical components, such as waveplates, lenses, beam splitters etc. that on the other hand belong to standard optical components in other frequency ranges. G. silicon lenses, tsurupica lenses or polyethylene lenses, most of them usually introduce strong spherical aberrations since the underlying focussing principle is purely based on refraction phenomena at curved boundaries None of these lenses can possess adaptively controllable optical properties. We present an alternative approach for the design and fabrication of ultra-thin THz lenses with strong focusing capabilities that is based on metamaterials with refractive index gradients Such thin, free-standing metamaterial membranes do enable the integration in very compact THz systems and possess the potential to open up novel ways to realize a new class of adaptive THz optics that can be controlled by optical and/or electrical means [2, 3]
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