Low-loss polymers for terahertz applications
TL;DR: High-precision terahertz time-domain spectroscopy measurements on polymers (cross-linked polystyrene, TPX, Zeonor) from 0.2 to 4.2 THz show very interesting teraherstz and visible transparency.
Abstract: We have performed high-precision terahertz time-domain spectroscopy measurements on polymers (cross-linked polystyrene, TPX, Zeonor) from 0.2 to 4.2 THz. They show very interesting terahertz and visible transparency. We also investigated the terahertz characteristics of PDMS, a polymer extensively used in microfluidics, which showed absorption compatible with terahertz experiments. The thermoplastic properties of these polymers make them suitable for use as lens, window, waveguide, or support materials in such applications as biological imaging or microfluidics necessitating a constant visual control not provided by conventional silicon- or teflon-based devices.
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TL;DR: Terahertz (THz) spectroscopy holds large potential in the field of nondestructive, contact-free testing as mentioned in this paper, and the ongoing advances in the development of THz systems, as well as the appearance of the first related commercial products, indicate that large-scale market introduction of THZ systems is rapidly approaching.
Abstract: Terahertz (THz) spectroscopy, and especially THz imaging, holds large potential in the field of nondestructive, contact-free testing. The ongoing advances in the development of THz systems, as well as the appearance of the first related commercial products, indicate that large-scale market introduction of THz systems is rapidly approaching. We review selected industrial applications for THz systems, comprising inline monitoring of compounding processes, plastic weld joint inspection, birefringence analysis of fiber-reinforced components, water distribution monitoring in polymers and plants, as well as quality inspection of food products employing both continuous wave and pulsed THz systems.
406 citations
20 Jun 2017
TL;DR: In this paper, a metasurface consisting of sub-wavelength cylindrical resonators is proposed to achieve diffraction-limited imaging at terahertz frequencies without cooling.
Abstract: Imaging in the terahertz (THz) range of the electromagnetic spectrum is difficult owing to the lack of high-power sources and efficient detectors. For decades, there has been tremendous effort to fashion focal plane arrays for THz imaging owing to the great number of potential applications. Here, we propose and demonstrate an alternative approach which utilizes all-dielectric metasurface absorbers that act as universal converters of radiation. Incident THz waves are absorbed by the metasurface, converted to heat, and subsequently detected by an infrared camera. We realize a metasurface consisting of sub-wavelength cylindrical resonators that achieve diffraction-limited imaging at THz frequencies without cooling. The low thermal conductivity and diffusivity significantly limit the thermal conduction between neighboring pixels, thus improving the spatial resolution and imaging time. Similar to conventional metallic-based metamaterials, our all-dielectric metasurface absorber can be scaled to other bands of the electromagnetic spectrum, offering a blueprint to achieve novel uncooled bolometric imaging.
183 citations
TL;DR: It is shown that inexpensive 3D printed THz diffractive lenses can be reliably used in focusing and imaging THz systems and are capable of extended depth of focus or bifocalization.
Abstract: A 3D printer was used to realize custom-made diffractive THz lenses. After testing several materials, phase binary lenses with periodic and aperiodic radial profiles were designed and constructed in polyamide material to work at 0.625 THz. The nonconventional focusing properties of such lenses were assessed by computing and measuring their axial point spread function (PSF). Our results demonstrate that inexpensive 3D printed THz diffractive lenses can be reliably used in focusing and imaging THz systems. Diffractive THz lenses with unprecedented features, such as extended depth of focus or bifocalization, have been demonstrated.
104 citations
16 Jan 2017
TL;DR: Emerging concepts based on commercial ceramic technologies, micromachining, and 3-D printing technologies for compact and lightweight packaging in practical applications are highlighted, along with metallic split blocks with rectangular waveguides, which are still considered the most valid and reliable approach.
Abstract: In the last couple of decades, solid-state device technologies, particularly electronic semiconductor devices, have been greatly advanced and investigated for possible adoption in various terahertz (THz) applications, such as imaging, security, and wireless communications. In tandem with these investigations, researchers have been exploring ways to package those THz electronic devices and integrated circuits for practical use. Packages are fundamentally expected to provide a physical housing for devices and integrated circuits (ICs) and reliable signal interconnections from the inside to the outside or vice versa . However, as frequency increases, we face several challenges associated with signal loss, dimensions, and fabrication. This paper provides a broad overview of recent progress in interconnections and packaging technologies dealing with these issues for THz electronics. In particular, emerging concepts based on commercial ceramic technologies, micromachining, and 3-D printing technologies for compact and lightweight packaging in practical applications are highlighted, along with metallic split blocks with rectangular waveguides, which are still considered the most valid and reliable approach.
90 citations
Cites background from "Low-loss polymers for terahertz app..."
...5 and 1 THz [15], [57]–[68] for direct comparison....
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TL;DR: A simple and versatile approach for fabricating terahertz lenses based on compression molding of micropowder polymer materials in a tabletop hydraulic press, confirming the excellent imaging qualities of the compression molded lenses.
Abstract: We present a simple and versatile approach for fabricating terahertz lenses based on compression molding of micropowder polymer materials in a tabletop hydraulic press. To demonstrate the feasibility of this approach, a biconvex lens shape is calculated using a ray-tracing algorithm and lenses based on two different micropowders are fabricated. As the powder materials have different refractive indices, the resulting lenses share the same geometric shape but differ in their respective focal length. The focusing properties of the lenses are evaluated by transversal and sagittal beam profile measurements in a fiber-coupled terahertz time-domain spectroscopy system, confirming the excellent imaging qualities of the compression molded lenses.
90 citations
Cites background from "Low-loss polymers for terahertz app..."
...In addition, specialized materials, such as Picarin [17], Zeonex [18], or Topas [17,19] are available, which, in addition to low losses, exhibit a similar refractive index at both THz and visible light frequencies, so that an optical prealignment of the THz path becomes possible....
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References
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IBM1
TL;DR: In this paper, the authors measured the far-infrared absorption and dispersion from 0.2 to 2 THz of the crystalline dielectrics sapphire and quartz, fused silica, and the semiconductors silicon, gallium arsenide, and germanium.
Abstract: Using the method of time-domain spectroscopy, we measure the far-infrared absorption and dispersion from 0.2 to 2 THz of the crystalline dielectrics sapphire and quartz, fused silica, and the semiconductors silicon, gallium arsenide, and germanium. For sapphire and quartz, the measured absorptions are consistent with the earlier work below 0.5 THz. Above 1 THz we measure significantly more absorption for sapphire, while for quartz our values are in reasonable agreement with those of the previous work. Our results on high-purity fused silica are consistent with those on the most transparent fused silica measured to date. For the semiconductors, we show that many of the previous measurements on silicon were dominated by the effects of carriers due to impurities. For high-resistivity, 10-kΩ cm silicon, we measure a remarkable transparency together with an exceptionally nondispersive index of refraction. For GaAs our measurements extend the precision of the previous work, and we resolve two weak absorption features at 0.4 and 0.7 THz. Our measurements on germanium demonstrate the dominant role of intrinsic carriers; the measured absorption and dispersion are well fitted by the simple Drude theory.
2,084 citations
TL;DR: It is shown how a simple waveguide, namely a bare metal wire, can be used to transport terahertz pulses with virtually no dispersion, low attenuation, and with remarkable structural simplicity.
Abstract: Sources and systems for far-infrared or terahertz (1 THz = 10(12) Hz) radiation have received extensive attention in recent years, with applications in sensing, imaging and spectroscopy. Terahertz radiation bridges the gap between the microwave and optical regimes, and offers significant scientific and technological potential in many fields. However, waveguiding in this intermediate spectral region still remains a challenge. Neither conventional metal waveguides for microwave radiation, nor dielectric fibres for visible and near-infrared radiation can be used to guide terahertz waves over a long distance, owing to the high loss from the finite conductivity of metals or the high absorption coefficient of dielectric materials in this spectral range. Furthermore, the extensive use of broadband pulses in the terahertz regime imposes an additional constraint of low dispersion, which is necessary for compatibility with spectroscopic applications. Here we show how a simple waveguide, namely a bare metal wire, can be used to transport terahertz pulses with virtually no dispersion, low attenuation, and with remarkable structural simplicity. As an example of this new waveguiding structure, we demonstrate an endoscope for terahertz pulses.
1,047 citations
TL;DR: Utilizing terahertz time domain spectroscopy, the electromagnetic response of planar split ring resonators fabricated on GaAs is characterized and optical excitation is sufficient to turn off the electric resonance demonstrating the potential of SRR terAhertz switches.
Abstract: Utilizing terahertz time domain spectroscopy, we have characterized the electromagnetic response of a planar array of split ring resonators (SRRs) fabricated upon a high resistivity GaAs substrate. The measured frequency dependent magnetic and electric resonances are in excellent agreement with theory and simulation. For two polarizations, the SRRs yield a negative electric response ($ϵl0$). We demonstrate, for the first time, dynamical control of the electrical response of the SRRs through photoexcitation of free carriers in the substrate. An excited carrier density of $\ensuremath{\sim}4\ifmmode\times\else\texttimes\fi{}{10}^{16}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$ is sufficient to short the gap of the SRRs, thereby turning off the electric resonance, demonstrating the potential of such structures as terahertz switches. Because of the universality of metamaterial response over many decades of frequency, these results have implications for other regions of the electromagnetic spectrum.
844 citations
TL;DR: In this article, a novel method for fast and reliable extraction of material parameters in terahertz time-domain spectroscopy was proposed, which could be applied for most materials and requires neither simplifying assumptions nor samples of different thickness for the extraction.
Abstract: This paper introduces a novel method that allows fast and reliable extraction of material parameters in terahertz time-domain spectroscopy. This method could be applied for most materials and requires neither simplifying assumptions nor samples of different thickness for the extraction. The presented extraction procedure operates either on truncated terahertz signals when temporal windowing is possible, or on full ones otherwise. Some experimental examples covering all practical cases are given. In particular, the extraction procedure treats the tedious case of samples for which internal reflections of the terahertz pulse slightly overlap.
821 citations
"Low-loss polymers for terahertz app..." refers methods in this paper
...The experimental setup is based on the classical terahertz TDS setup [1,3]....
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...Equation (1) cannot be analytically solved, and a classical iterative method has been used with no approximation [3,20]....
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01 Oct 2007
TL;DR: Terahertz time-domain spectroscopy is used to study properties of nonpolar amorphous materials and the results were correlated with material properties.
Abstract: Terahertz time-domain spectroscopy is used to study properties of nonpolar amorphous materials. Terahertz absorption spectra and refractive indices were measured in a number of glasses, lubricating oils, and polymers, and the results were correlated with material properties.
420 citations