We present a metamaterial-based terahertz (THz) sensor for thickness measurements of subwavelength-thin materials and refractometry of liquids and liquid mixtures. The sensor operates in reflection geometry and exploits the frequency shift of a sharp Fano resonance minimum in the presence of dielectric materials. We obtained a minimum thickness resolution of 12.5 nm (1/16 000 times the wavelength of the THz radiation) and a refractive index sensitivity of 0.43 THz per refractive index unit. We support the experimental results by an analytical model that describes the dependence of the resonance frequency on the sample material thickness and the refractive index

In single-pixel coded aperture terahertz-imaging, the individual pixel size in the spatial terahertz modulator is usually comparable to the terahertz wavelength in order to obtain a sufficient spatial image resolution. Therefore, diffraction plays an important role in the imaging process and must be accurately taken into account when the image is computationally retrieved. For this reason, we analyzed the impact of diffraction from the spatial terahertz modulator on the quality of the reconstructed image in single-pixel coded aperture imaging. We observed that the most important fraction of the image information is already contained in the zero order diffracted radiation. Higher diffraction orders do not contain enough information to retrieve the image from them solely, yet can contribute to an improved image quality when added to the zero order information.

Efficient, high speed spatial modulators with predictable performance are a key element in any coded aperture terahertz imaging system. For spectroscopy, the modulators must also provide a broad modulation frequency range. In this study, we numerically analyze the electromagnetic behavior of a dynamically reconfigurable spatial terahertz wave modulator based on a micromirror grating in Littrow configuration. We show that such a modulator can modulate terahertz radiation over a wide frequency range from 1.7 THz to beyond 3 THz at a modulation depth of more than 0.6. As a specific example, we numerically simulated coded aperture imaging of an object with binary transmissive properties and successfully reconstructed the image.

We present a fabrication method for flexible optically tunable terahertz metamaterial membranes based on thinning and embedding of commercially available silicon wafers in the metamaterial structure. The resulting membrane thickness of less than 25 mu m allows for quasi etalon-effect free devices which can be designed to show impedance matching to the surrounding air. We fabricated a thin film spectral bandpass filter with a maximal transmission of 85% and a modulation depth upon optical tuning of 98% at an operating frequency of 0.65THz. Further, we discussed the charge carrier dynamics and the requirements for optical tuning

Many applications of terahertz technology are concerned with sensing of substances such as drugs, chemical compounds, explosives and much more. For this purpose, low-cost terahertz measurement systems are desired. In this respect, metasurfaces can be used as sensitive near-field sensors by exploiting the change of resonant frequency in the vicinity of substances. We demonstrate chip-based terahertz sensors that can be applied to measure the thickness of ultra-thin materials with a resolution of the order of 1/16000 of the wavelength. Furthermore, we show that the same sensor can be used for refractometric measurements. In this context, we evaluated the refractive index of highly absorptive liquids and liquid mixtures. Based on these measurements, we retrieved the mixing ratio of the liquid mixtures. Moreover, we show that meta-surfaces can be employed to implement chip-based terahertz circuits for highly confined surface waves. The electromagnetic properties of the meta-surface can be designed on purpose. For example, such meta-surfaces can serve as integrated interferometric sensors and can be used for highly sensitive measurements when only a small amount of a sample material is available. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only