Search

Highly sensitive terahertz (THz) sensors for a myriad of applications are rapidly evolving. A widespread sensor concept is based on the detection of minute resonance frequency shifts due to a targeted specimen in the sensors environment. Therefore, cutting-edge high resolution continuous wave (CW) THz spectrometers provide very powerful tools to investigate the sensors' performances. However, unpredictable yet non negligible frequency drifts common to state-of-the-art CW THz spectrometers limit the sensors' accuracy for ultra-high precision sensing and metrology. Here, we overcome this deficiency by introducing an ultra-high quality (Q) THz microresonator frequency reference. Measuring the sensor's frequency shift relative to a well-defined frequency reference eliminates the unwanted frequency drift, and fully exploits the capabilities of modern CW THz spectrometers as well as THz sensors. In a proof-of-concept experiment, we demonstrate the accurate and repeated detection of minute resonance frequency shifts of less than 5MHz at 0.6THz of a THz microresonator sensor.

Die Unternehmensberichterstattung entwickelt sich äußerst dynamisch weiter. Gerade nichtfinanzielle Berichterstattungselemente wenden sich an einen immer breiteren Stakeholderkreis. Welche Berichtpflichten von welchen Unternehmen in welchen Formaten für welche Adressaten offenzulegen sind, nehmen 30 Experten in diesem Handbuch systematisch in den Blick. Teil 1 zeigt für die verschiedenen Berichtselemente neben Berichtsinhalten, Anwenderkreisen, Zielsetzungen, Gestaltungsmöglichkeiten und prüfungsrechtlichen Anforderungen auch neue Kommunikationswege auf. Teil 2 beleuchtet die Sicht der unterschiedlichen Stakeholdergruppen. Erfahrene Repräsentanten verdeutlichen die sich ändernden Erwartungen der Standardsetter, Unternehmen verschiedener Größe, Abschlussprüfer, Investoren, Arbeitnehmervertreter und NGOs.

We demonstrate a terahertz (THz) frequency reference for precision metrology, by utilising the inherently well- defined resonance frequencies of ultra-high quality (Q) THz microresonators. In a proof-of-concept experiment, we demonstrate the accurate and repeated detection of minute resonance frequency shifts of less than 5 MHz at 0.6 THz of a THz microresonator sensor.

Coherent continuous wave (CW) terahertz spectroscopy is an extremely valuable technique that allows for the interrogation of systems that exhibit narrow resonances in the terahertz (THz) frequency range, such as high-quality (high-Q) THz whispering-gallery mode resonators. Unfortunately, common implementations are dramatically impaired by deficiencies in the used data analysis schemes. Here, we show that the physics of the problem presents an elegant solution whose full potential has remained overlooked until now. We argue that, thanks to the causality of physical systems, Hilbert transformation can be used to analyze the frequency response of linear systems with arbitrarily narrow resonance features in coherent CW THz spectroscopy. In particular, by establishing that signals encountered in typical experiments are closely related to analytic signals, we demonstrate that Hilbert transformation is applicable even when the envelope varies rapidly compared to the oscillation period.

Terahertz (THz) technology is rapidly evolving, and the advancement of data and information processing devices is essential. Silicon THz microresonators provide perfect platforms to develop compact and integrated devices that could transform THz technology. Here we present a systematic study on the key figure of merit of silicon THz disc microresonators - the quality factor (Q-factor) - in dependence on the substrate’s resistivity. Our results show that the Q-factor depends linearly on the resistivity and a variation in resistivity from 10 kΩcm to 15 kΩcm changes the Q-factor from 50k to 76k at 0.6 THz. Moreover, we experimentally determine that the silicon material absorption is inversely proportional to the substrate’s resistivity. In general, the presented methodology is ideally suited to precisely measure the material absorption of low-loss materials in the THz domain, which is challenging using conventional THz spectroscopy.

Form und Gestalt stadtischer Strasen- und Wegenetze – in Grose und Masstablichkeit, in Raumfolgen und Abmessungen, in Aufteilung und Art der Oberflachen, in der Eignung als erweiterte Nutzflache fur Anlieger, als Orte der Begegnung und des Austausches – unterliegen dem Einfluss gesellschaftlicher, okonomischer und technischer Randbedingungen der jeweiligen Epoche. Erst als Folge der Industrialisierung verandern sich die jahrhundertelang fur den Fusverkehr, fur Reittiere, fur von Tieren gezogene Wagen, aber auch fur Markte und Veranstaltungen, fur Prasentation und Reprasentation konzipierten Netze von Strasen, Wege und Platze grundlegend. Die Massenmotorisierung fuhrt zum Verlust uberkommener Qualitaten. „Trennung statt Integration“ ist die Devise dieser Epoche fur die Gestaltung von Autostrasen als Teil offentlicher Raume. Mit Radialringlosungen und Tangentenpolygonen im ubergeordneten Strasennetz und Raster-, Innen- oder Ausenringsystemen im untergeordneten Erschliesungsstrasennetz entstehen hierarchisch funktional strukturierte, in erster Linie am Kraftfahrzeugverkehr ausgerichtete Netze. Die in vielfacher Hinsicht negativen Folgen einseitiger Autoorientierung leiten einen Paradigmenwechsel ein. Unter dem Motto „Flachenhafte Verkehrsberuhigung“ im umfassenden Sinne geht es im Stadtverkehr der letzten Dekaden um ein breites Bundel an Strategien und Masnahmen. „Integration statt Trennung“ verlangt die Ruckkehr zu vertragliche(re)n Geschwindigkeiten: Verkehrsberuhigte Bereiche mit Schrittgeschwindigkeit, Tempo-30- bzw. Tempo-20-Zonen, Fahrradstrasen mit Tempo 30 und zugelassenem Autoverkehr von Anliegern sowie Shared-Space-Losungen sind die neuen, modifizierten Elemente integrierter stadtischer Strasen- und Wegenetze. Erst mit der Ruckbesinnung auf die Vielfalt der materiellen wie immateriellen Anspruche im offentlichen Raum nimmt die Einsicht zu, dass auch Funktionen wie Orientierung und Identitat, Lesbarkeit von Raumstruktur und Stadtgrundriss, Verdeutlichung der Stadtgestalt und Erzeugung von Stadtbild Werte einer Baukultur sind, die mit Erkennen, Beachten und Erleben historischer Bezuge des Strasen- und Wegenetzes unmittelbar zusammenhangen.

We report on the first demonstration of a THz gas spectrometer using a sub-wavelength thick ultrahigh-Q THz disc microresonator. Leveraging the microresonator's ultrahigh quality factor in excess of 120,000 and the intrinsically large evanescent field, allows for the implementation of a very compact spectrometer without the need for complex multi-pass gas cells. Water vapor concentrations as low as 4 parts per million at atmospheric conditions have been readily achieved in these proof-of-concept experiments.

We report on a Terahertz (THz) silicon disc microresonator with a quality factor (Q-factor) in excess of 120,000 at 0.6 THz. The ultra-high Q-factor is enabled by thinning the disc to a fraction of the free-space wavelength, thus minimising the impact of the silicon material absorption. This novel class of ultrahigh-Q microresonators provides excellent opportunities for a myriad of applications and unprecedented possibilities for light-matter interaction in the THz domain.

We introduce a frequency-domain terahertz (THz) spectrometer based on a comb locked frequency synthesizer which combines > 3 THz scanning range at rates > 0.3 THz/s. We demonstrate kHz frequency resolution in THz precision spectroscopy of ultrahigh-Q whispering-gallery mode resonators.

The terahertz spectrum provides tremendous opportunities for broadband gas-phase spectroscopy, as numerous molecules exhibit strong fundamental resonances in the THz frequency range. However, cutting-edge THz gas-phase spectrometer require cumbersome multi-pass gas cells to reach sufficient sensitivity for trace level gas detection. Here, we report on the first demonstration of a THz gas-phase spectrometer using a sub-wavelength thick ultrahigh-Q THz disc microresonator. Leveraging the microresonator’s ultrahigh quality factor in excess of 120,000 as well as the intrinsically large evanescent field, allows for the implementation of a very compact spectrometer without the need for complex multi-pass gas cells. Water vapour concentrations as low as 4 parts per million at atmospheric conditions have been readily detected in proof-of-concept experiments.

Zusammenfassung In jüngerer Zeit zeigen sich zunehmend Belegschaftsgenossenschaften, welche energiegenossenschaftliche Förderaufträge auf den betrieblichen Kontext ausweiten. Beispiele zeigen: Es sind die Beschäftigten, die als Mitglieder „ihrer“ Genossenschaft die Energiewende weiter vorantreiben. Neue betriebliche Genossenschaftsmodelle tragen zur Attraktivität des Arbeitgebers bei und sind somit auch eine Option, einem drohenden Fachkräftemangel zu begegnen.

We report on free-space coupling of high quality (Q) spherical THz whispering-gallery mode resonators (WGMRs) as a simple alternative to more complex waveguide and prism coupling. Excitation efficiencies up to 50% to WGMs with Q-factors of $1.5 {\times} 10 ^{4}$ at 0.7THz are achieved.

We report on the first demonstration of an anomalous blue-shift of whispering-gallery modes (WGMs) using metallic substrates. The results allow for frequency tuning of WGMs essential for numerous applications, and establish novel insights into the anomalous blue-shift of WGM cavity systems.

Artificial structures that exhibit narrow resonance features are key to a myriad of scientific advances and technologies. In particular, exploration of the terahertz (THz) spectrum—the final frontier of the electromagnetic spectrum—would greatly benefit from high-quality resonant structures. Here we present a new paradigm of terahertz silicon disc microresonators with subwavelength thickness. Experimental results utilizing continuous-wave THz spectroscopy establish quality factors in excess of 120,000 at 0.6 THz. Reduction of the disc thickness to a fraction of the wavelength reduces the losses from the silicon substrate and paves the way to unparalleled possibilities for light–matter interaction in the THz frequency range.

We report on prism coupling of high-quality (high-Q) terahertz (THz) whispering-gallery modes (WGMs) in spherical high resistivity float zone grown silicon (HRFZ-Si) resonators over two octaves from 0.2 THz to 1.1 THz. The WGMs are excited using a HRFZ-Si prism and show unprecedented quality factors of up to 2.2 × 104. A detailed discussion of the phase-and mode-matching criteria of the prism coupling scheme implemented in the continuous wave THz spectroscopy system is presented. The results provide numerous opportunities for passive ultra-broadband high-Q devices operating in the THz frequency range.

Whispering gallery mode (WGM) resonators are compelling optical devices; however, they are nearly unexplored in the terahertz (THz) domain. In this Letter, we report on THz WGMs in quartz glass bubble resonators with a subwavelength wall thickness. An unprecedented study of both the amplitude and phase of THz WGMs is presented. The coherent THz frequency domain measurements are in excellent agreement with a simple analytical model and results from numerical simulations. A high finesse of 9 and a quality (Q) factor exceeding 440 at 0.47 THz are observed. Due to the large evanescent field, the high Q-factor THz WGM bubble resonators can be used as a compact, highly sensitive sensor in the intriguing THz frequency range.

Micro ring and micro bubble resonators are of enormous importance in the optical regime [1], [2], however little work has yet been done in the terahertz (THz) realm [3]. In this work we present simulations and measurements of whispering gallery modes (WGMs) in a dielectric bubble resonator at THz frequencies. The resonators are numerically analyzed with both finite element method as well as Mie scattering theory. The experiments are performed with a continuous wave THz spectrometer. At critical coupling a very high Q-factor of more than 400 at 0.465 THz is experimentally observed. The measured Finesse of the THz bubble resonator is ∼ 9. The enormous potential of bubble WGM THz resonators for sensing applications are discussed.

Zusammenfassung Der vorliegende Beitrag beschäftigt sich mit der Rolle von Produktivgenossenschaften bei Unternehmenskrisen und Unternehmensnachfolgen. Wir präsentieren zunächst einen Überblick über die theoretische und empirische Literatur und konfrontieren diese mit den bisherigen praktischen Erfahrungen in Deutschland. Auf dieser Basis arbeiten wir heraus, wann und wie Produktivgenossenschaften einen Betrag zur Stabilisierung kleiner und mittlerer Unternehmen leisten können.

We report on the coupling of a free-space Gaussian beam to symmetric high-quality (Q) whispering-gallery mode resonators (WGMRs) for terahertz (THz) radiation. We achieve very high excitation efficiencies up to 50% to THz WGMs with a Q-factor of 1.5×104 at 0.7 THz. The high coupling efficiencies have been realized by leveraging a Gaussian beam with a nearly diffraction-limited focal spot, as well as readily available low-loss, high-index silicon spheres with diameters comparable to the wavelength. The results convincingly underline the viability of free-space coupling in the THz frequency range.

The vast majority of resonant systems show a red-shift for the resonance frequency when a perturbation, e.g., losses, is introduced to the system. In contrast, here we report for the first time, to the best of our knowledge, the experimental demonstration of both red- and anomalous blue-shifting of whispering-gallery modes (WGMs) using dielectric and metallic substrates. The maximum blue-shift is more than three times as large as the expected red-shift, proving that the anomalous blue-shift is more than a peculiar curiosity. The experiments are performed in the terahertz frequency range with coherent continuous-wave spectroscopy. The results establish dielectric and metallic tuning as a novel and viable approach to tune high-quality WGMs and provide valuable insights into the anomalous blue-shift of WGM cavity systems. The tuning capabilities for these compact monolithic resonators are of significant interest for fundamental science and technological applications alike.

Zusammenfassung In der gesellschaftlichen Debatte um ein Mehr an Wirtschaftsdemokratie in Zeiten von Shareholder-Value und übertriebener Profitmaximierung geraten vermehrt alternative Unternehmensformen in den Blickwinkel. Speziell Genossenschaften mit ihren Eckpfeilern von Gleichheit, Selbsthilfe und Solidarität werden häufig von vornherein mit einer demokratischen Ausrichtung in Verbindung gebracht. Genossenschaften stehen für ein demokratisches Miteinander und für ein auskömmliches, nachhaltiges Wirtschaften zur Erfüllung unterschiedlichster Bedürfnisse. Zu beobachten ist, dass diese Wirkung sich erfreulicherweise in neuen genossenschaftlichen Förderaufträgen abseits der traditionellen genossenschaftlichen Sektoren zeigt. In der Vielfalt der Eigentumsformen stellt die Genossenschaft einen zunehmend an Bedeutung gewinnenden Baustein dar.

We report on the implementation of a metal ridge spoof plasmon waveguide of micro pillars in a hexagonal lattice for guidance of Terahertz (THz) radiation. Finite-difference time-domain (FDTD) simulations demonstrate broadband, low-loss and low dispersion guidance between 0.30 THz to 0.65 THz. A very high 2D coupling efficiency can be achieved with a common linearly polarized Gaussian beam source. 3D FDTD simulations are presented to study the impact of finite pillar height on the dispersion relation and mode distribution. An experimental realization of the micro pillars based on femtosecond laser machining of micro holes in a Polystyrene (PS) template is presented.

We numerically study the guidance properties of a dielectric tube Terahertz (THz) waveguide with an antireflection (AR) structure to efficiently extend the bandwidth of a low loss dielectric tube waveguide. The results obtained from the 3D finite-difference time-domain (FDTD) simulations are in excellent agreement with THz time-domain spectroscopy (THz-TDS) measurements of 3D-printed prototypes of the novel THz waveguides. The presented AR-structure consists of dielectric close-packed cones arranged in a hexagonal lattice on the outer circumference of the dielectric tube. With feature sizes of about 600 μm and 1200 μm the investigated cones are in the order of the wavelength between 0.2THz to 1THz.

We investigate guidance of Terahertz (THz) radiation in metallic and 3D-printed dielectric helical waveguides in the frequency range from 0.2 to 1 THz. Our experimental results obtained from THz time-domain spectroscopy (THz-TDS) measurements are in very good agreement with finite-difference time-domain (FDTD) simulations. We observe single-mode, low loss and low dispersive propagation of THz radiation in metallic helical waveguides over a broad bandwidth. The 3D-printed dielectric helical waveguides have substantially extended the bandwidth of a low loss dielectric tube waveguide as observed from the experimental and simulation results. The high flexibility of the helical design allows an easy incorporation into bench top THz devices.

We investigate thermal tuning of an ultra-high quality (Q) terahertz (THz) whispering-gallery mode resonator (WGMR) made of low loss silicon. The Si THz WGMR can be continuously tuned with a rate of about 29 MHz/K in the frequency range from 650 GHz to 666 GHz. Furthermore, we utilize the Si WGMR to extract the thermo-optic coefficient of Si at 459 GHz and 659 GHz in the temperature range from 295 K to 363 K.

We report on the first experimental demonstration of terahertz (THz) whispering-gallery modes (WGMs) with an ultra high quality (Q) factor of $1.5 \times {10}^{4}$ at 0.62THz. The WGMs are observed in a high resistivity float zone silicon (HRFZ-Si) spherical resonator coupled to a sub-wavelength silica waveguide. A detailed analysis of the coherent continuous wave (CW) THz spectroscopy measurements combined with a numerical model based on Mie-Debye-Aden-Kerker (MDAK) theory allows to unambiguously identify the observed higher order radial THz WGMs.

We report on a 3D-printed helical waveguide to increase the bandwidth of a low-loss dielectric tube Terahertz (THz) waveguide. The helical design prevents the multiple reflections in the tube cladding hence avoiding the pronounced interference pattern in the attenuation spectrum of a dielectric tube waveguide. Both THz time-domain spectroscopy (THz-TDS) measurements and finite-difference time-domain (FDTD) simulations consistently confirm the extended bandwidth of the dielectric helical waveguide. In addition, numerical investigations reveal that the broadband behavior of the 3D-printed helical waveguide is not critical with respect to the absorption of the waveguide material.

We report on Fano resonances in a high-quality (Q) whispering-gallery mode (WGM) spherical resonator coupled to a multi-mode waveguide in the terahertz (THz) frequency range. The asymmetric line shape and phase of the Fano resonances detected with coherent continuous-wave (CW) THz spectroscopy measurements are in excellent agreement with the analytical model. A very high Q factor of 1600, and a finesse of 22 at critical coupling is observed around 0.35 THz. To the best of our knowledge this is the highest Q factor ever reported for a THz WGM resonator.

We report on data processing for continuous wave (CW) terahertz (THz) spectroscopy measurements based on a Hilbert spectral analysis to achieve MHz resolution. As an example we investigate the spectral properties of a whispering gallery mode (WGM) THz bubble resonator at critical coupling. The experimental verification clearly demonstrates the significant advantages in relative frequency resolution and required acquisition time of the proposed method over the traditional data analysis. An effective frequency resolution, only limited by the precision and stability of the laser beat signal, can be achieved without complex extensions to a standard commercially available CW THz spectrometer.

We experimentally observe broadband Terahertz pulse propagation in flexible metal helix waveguides. Our measurements are in very good agreement with finite-difference time domain simulations. The waveguides have a constant attenuation coefficient of 0.2 cm−1 in the region between 0.3 and 0.9 THz. The measured temporal signals indicate that the THz pulse is confined to the core of the helical waveguide. Moreover, a constant magnitude of the group-velocity dispersion parameter of less than 1 ps THz−1 cm−1 in the region from 0.5 THz to 0.9 THz reveals the low dispersive behavior of the helical waveguide.

The cloud point curve of aqueous solutions of poly(N-isopropylacrylamide), poly(N-isopropylmethacrylamide) and their statistical copolymers were determined turbidimetrically. All the Systems demix upon heating at the cloud point temperature and mix reversibly upon cooling. The cloud points are independent of the total concentration of the solutions (dilute range) and of the sample thickness. Mixtures of the homopolymers poly(N-isopropylacrylamide) and poly(N-isopropylmethacrylamide) in water (ternary systems) exhibit two cloud points, which are nearly the same as the cloud points of the two binary systems homopolymer/water. A quantitative correlation was found between the cloud point temperatures of copolymers of N-isopropylacrylamide and N-isopropylmethacrylamide and the composition of the latter.

The integrity and function of encapsulated parathyroid tissue following xenotransplantation is limited by oxygen and nutrition supply and capsule fibrosis. Since some of these factors depend on stability and biocompatibility of the coating material, multilayer microcapsules have been developed. Parathyroid tissue pieces and digested single cells from pigs were encapsulated in barium-alginate and in polyacrylic acid (PAA) multilayer capsules. After 7 days of culture the function of the encapsulated cells were assessed. Subsequently, in a part of the cultured microcapsules the viability was directly assessed whereas the other part was transplanted in dark animal [DA] rats for 30 days. After explantation viability and fibrotic reaction were examined. Single cells showed a significant increase in parathyroid hormone [PTH] secretion when exposed to medium low in calcium, whereas minced tissue pieces revealed necrosis without stimulatory responsiveness. Morphometry showed significantly better viability of single cells compared with minced tissue in vitro and in vivo. The fibrotic reaction against capsules with minced tissue was more pronounced than for capsules containing single cells. There was no difference between barium alginate and PAA capsules when containing minced tissue. In single cells, however, the fibrous tissue reaction differed significantly between barium alginate and PAA capsules. Encapsulated single cells of parathyroid tissue maintain detectable function and viability. In contrast minced tissue underwent necrosis and induced significantly more connective tissue reaction than single cells indicating an interrelationship between necrosis and fibrosis.

The formation of tetrakis(benzo-3,4-dihydro-1,3-oxazines) 2 by condensation of resorcarenes 1 with various primary amines and an excess of formaldehyde is not only regioselective but, in the case of (R)- or (S)-1-phenylethylamine and their para-substituted (Br, Me) derivatives, also completely diastereoselective. The reaction with the structurally similar (R)-1-aminoindane and (S)-1-(1-naphthyl)ethylamine, on the other hand, produced only a slight excess of one of the two possible epimers 2 and with (R)-1-cyclohexylethylamine no diastereoselectivity was found at all. The presence and the ratio of both diastereomeric structures can be clearly determined by NMR spectroscopy. Inspection of partly converted reaction mixtures suggests that the preferred crystallisation of one of the epimers is responsible for the diastereoselectivity observed in the case of 1-phenylethylamines and not an entirely diastereoselective reaction. The identity of 3, a cyclic triamine obtained as a side product of the Mannich reaction with (R)-1-aminoindane, was established by single crystal X-ray structure analysis.