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A carrier-envelope phase (CEP) shifter for broadband terahertz (THz) pulses was demonstrated. The CEP, the phase of the carrier frequency with respect to the peak of the THz pulses, is a key element in light-matter interactions in high fields, especially when few-cycle pulses are used. The CEP shifter was constructed by suitably arranging several prism wave plates. By rotating the wave plates, we...
In terahertz spectroscopy, multi-layered samples often need to be measured, for instance in a liquid flow cell, and this complicates the extraction of material parameters. We present a spectroscopic parameter extraction algorithm for multilayer samples that can also be used to extract the thickness of an unknown sample layer.
It is commonly believed that most of naturally occurring transparent materials have small positive refractive indices around 1 in the terahertz waveband. However, metamaterials have made a paradigm shift and achieve the design of man-made materials with both on-demand electromagnetic properties and unprecedented refractive indices. Here, inspired by the metamaterial concept, we report a transparent...
In this paper we show how the act of measuring skin in vivo using a standard terahertz reflection imaging system affects the terahertz response. We found that even 5 seconds occlusion by the imaging window caused subtle changes in the THz response. As the occlusion time increases, the skin's surface water content increases which causes the refractive index of the skin to increase. This in turn leads...
We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. The artificial-dielectric medium is made up of a stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. The lens is capable of focusing a 2 cm diameter...
We present a simple data processing technique that effectively removes undesired signals and extracts hidden sample-induced echoes, accurately determining material parameters in ambient atmosphere. The method is validated by demonstrating refractive index and thickness calculations in transmission and reflection terahertz time-domain measurements.
For ex vivo biological imaging, sample handling can affect image contrast. We investigate the effects of the slow freeze-thaw cycle on the THz properties of porcine lean and fat tissues. Lean tissues showed a significant decrease in the refractive index after the freeze-thaw cycle while there was no significant change observed in THz properties of fat tissues.
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