The Infona portal uses cookies, i.e. strings of text saved by a browser on the user's device. The portal can access those files and use them to remember the user's data, such as their chosen settings (screen view, interface language, etc.), or their login data. By using the Infona portal the user accepts automatic saving and using this information for portal operation purposes. More information on the subject can be found in the Privacy Policy and Terms of Service. By closing this window the user confirms that they have read the information on cookie usage, and they accept the privacy policy and the way cookies are used by the portal. You can change the cookie settings in your browser.
Here we demonstrate the experimental results on in-house fabricated polymer THz porous fiber with sub-wavelength features. The experimental results confirm the theoretical prediction of low dispersion characteristics in a THz porous fiber as compared to a microwire.
We present a photoconductive probe-tip applicable for near- and far-field measurements in the terahertz frequency range. The probe-tip is based on a triangular patch of freestanding LT-GaAs of only 1.3 mum thickness with a pair of tapered metallic wires on top. Using non-resonant electric field enhancement at the tip of the probing device a spatial resolution of 5 mum and a bandwidth of 2 THz is demonstrated.
Photoconductive aperture antenna arrays are used in THz time domain systems as the transmitter and the receiver elements, and the radiation properties of the antennas are characterized in terms of the applied dc bias and the optical excitation power.
We investigate asymmetric split ring resonators (SRR) for the THz frequency range. These SRRs exhibit sharp resonances and strong field localization, which is of potential interest e.g. for biosensing of minute amount of sample material. Our near-field measurements show the local response of the SRRs on a scale much smaller than the resonance wavelength of 320 mum. Fig. 1 depicts the spatially resolved...
High-speed asynchronous optical sampling is used for the rapid and precise determination of transmission resonances of terahertz surface sensors based on asymmetric double split ring resonator arrays. The sensor response represented by a characteristic resonant frequency is determined to 0.66113 THz with an accuracy of plusmn325 MHz within 2 seconds of read-out time.
Various motion input and sensing methods have been evaluated in designing a home-based physiotherapy rehabilitation system for spinal cord injury patients. The important design factors include; the ability of the system to track human motion such that the requirements of a game input and data logging software are met; the ability to modify the platform to suit the existing and possible future requirements;...
We present results on THz near-field measurements of sub-wavelength single holes made in metal. Time and frequency dependence of the electric near-field of single sub-wavelength apertures are compared with the near-field predictions made by the well-known Bethe-Bouwkamp model.
An array of sub-wavelength circular apertures (d=60 mum), periodically distributed in a square lattice, was studied in the near field using Terahertz Time-Domain Spectroscopy (THz-TDS). Images of the complete electric field distribution (Emacrx,Emacry,Emacrz) were recorded over a subsection of the array, as well as the corresponding spectral information, with a spatial resolution Lt10 mum.
Optical scanning methods for characterizing radiation properties of THz photoconductive antenna arrays are proposed, and as an example, a fourteen element equally spaced array structure made on low temperature grown GaAs (LT-GaAs) is characterized using the proposed methods.
Ionization gating confines high-harmonic generation to the leading edge of the driver pulse. Experimentally produced soft-x-ray continuous radiation is spectrally broad and tunable. The method suggests isolated attosecond-pulse production with long driver pulses.
Despite the classic stresses on insulation systems, repetitive voltage pulses are more and more present in modern power systems. Their influence is yet quite unknown. Considering the large slew and repetition rates of HVDC valves with voltage-sourced converters, high frequency noise is generated and subjected to the insulation systems, e.g. oil and cellulose, used in transformers. For an assessment...
Octave-spanning laser pulses enable a new coherent control scheme based on the carrier-envelope phase (CEP). Multiphoton ionization of Xe atoms demonstrates CEP control over the phases of photoelectron quantum states and therefore the photoelectron direction.
We present results on THz near-field measurements of sub-wavelength apertures in metal films. Our results allow us to test, with unprecedented detail, the near-field predictions made by the well-known Bethe-Bouwkamp model.
Ionization gating confines high-harmonic generation to the leading edge of the driver pulse. Experimentally produced soft-x-ray continuous radiation is spectrally broad and tunable. The method suggests isolated attosecond-pulse production with long driver pulses.
We present results on THz near-field measurements of sub-wavelength apertures in metal films. Our results allow us to test, with unprecedented detail, the near-field predictions made by the well-known Bethe-Bouwkamp model.
In this paper, a metallic waveguide concept that combines dispersion-free and low-loss propagation characteristics with two-dimensional mode confinement over a broad frequency range. Waveguide consists of two planar arranged metalized slabs of 300 mum thickness separated by a 270 mum wide slit. The width a of each slab in x-direction is 20 mm and is considered as quasi-infinite in terms of the propagating...
This paper presents simulation and experimental results of a metallic wire-pair structure (H-pair) negative-index materials (NIM) and examine the dielectric characteristics of this structure in the THz frequency range using THz time-domain spectroscopy (TDS). This structure possesses negative index features at normal incidence. This makes measurements, that are otherwise difficult to carry out, possible...
In this work, fabrication and characterization of a negative-index metamaterial consisting of free-standing wire-pair composite structures is presented for application at THz frequencies. Complex index of refraction data is derived from amplitude- and phase-sensitive THz time-domain transmission and reflection measurements and compared with theoretical results. A first direct measurement of a negative...
Equivalent surface impedance is proposed to model an ultra-thin DNA monolayer in numerical simulations of THz bio-chips. Surface impedance model not only improves the accuracy, but also saves a large amount of computational resources compared to thin film dielectric model. Applying the proposed model to an existing bio-chip device predicts that electromagnetic properties of an ultra-thin DNA monolayer...
Single element coplanar strip-line photoconductive (PC) emitters remain to date the most common means of generating an detecting sub-picosecond terahertz radiation. These antennas however, suffer from excitation power limitations leading to relatively early saturation. It is possible to overcome such limitations by using several radiating elements arranged as an array. We present an array structure...
Set the date range to filter the displayed results. You can set a starting date, ending date or both. You can enter the dates manually or choose them from the calendar.