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One can observe terahertz (THz) radiation from various kinds of materials, when excited with a femtosecond laser, owing to ultrafast current modulation. THz waves reflect various kinds of properties such as local electric field, particularly ultrafast transient phenomena, in their waveforms. The observation of the THz waveforms enables us to explore ultrafast nature of electronic materials and devices...
We investigated the use of low-temperature-grown (LTG) GaAs photoconductive antenna (PCA) excited at 1560 nm for the detection of terahertz (THz) pulses. The decrease in the excitation spot size with a PCA of properly reduced gap length was found to be efficient to enhance the signal intensity. With a spot size of 2.7 μm exciting a 1.5 μm gap PCA, the amplitude of the detected THz wave is an order...
In this contribution we review some of our recent result in achieving power transmission enhancement through sub-wavelength apertures at both microwaves and optical frequencies. We aim at exciting highly localized magnetic resonances in order to design devices whose size is comparable to that of the aperture and suitable, thus, for practical applications. The proposed approaches may be applied indeed...
In this contribution we propose a review of our latest results in applying the scattering cancellation technique to cloak complex objects, both at microwave and optical frequencies. Different configurations based on the employment of metamaterials are reviewed, analyzing their performances through proper figures of merit and discussing the fundamental aspects of design procedure. Our theoretical models...
We have used the Pockels effect in ZnTe to demonstrate that the frequency and the phase of Quantum Cascade Lasers emitting at 2.4 and 2.7 Terahertz can be actively stabilized to the n-th harmonic of the 90 MHz repetition rate of a commercial, mode-locked Er-doped fiber-laser. The beating between the stabilized QCL frequency and the harmonic of the repetition rate yielded a signal-to-noise ratio >;...
Thin film deposition based on plasma CVD processes are well known for many years. While these processes mainly drove the miniaturization of wafer based micro electronics, the upscale was for a long time of minor interest. With the increasing activations in photovoltaic devices or flat panel displays, the homogeneous large area deposition became more important. This paper will contribute to handle...
In this paper, we consider the effect of the finite conductivity on the design of a radial line slot array (RLSA). Such an effect can be not negligible at high frequencies, especially when low cost metallization techniques are adopted. We show how this effect can be easily introduced in the numerical modeling of the antenna. As a matter of the fact, we extend the analytical evaluation of the dyadic...
The photo-Dember effect is known as source of impulsive THz radiation after excitation with femtosecond optical pulses. The origin of the emission is the ultrafast separation of electron and holes in strong carrier gradients due to different diffusion coefficients. For a simple semiconductor surface the time dependent polarization is oriented perpendicular to the excited surface which complicates...
Terahertz imaging and sensing have attracted much attention in recent years, because they can be applied to many application fields. A terahertz real-time imaging technologies considered increasingly important in the future (Terahertz Camera) was developed. The terahertz camera consists of a light source (Terahertz quantum cascade laser) and a un-cooled micro-bolometer array, which can easily get...
There has been an increasing interest in the use of terahertz electro-magnetic waves at frequencies of >;275 GHz with extremely large bandwidth for ultrahigh-speed wireless communications. This paper reviews our recent challenges towards 100-Gbit/s wireless communications using terahertz waves.
We report the investigation of two nonlinear optical phenomena which are related to intra-excitonic transitions in semiconductor quantum wells and thus occur in the THz range. This is, on one hand, the generation of THz sidebands of near-band gap radiation, a perturbative process, and on the other hand, the AC Stark effect manifested by the Autler-Townes splitting as a non-perturbative effect. Both...
Terahertz (THz) spectroscopy and THz imaging techniques are expected to have great potential for the noninvasive analysis of works of art. THz waves can penetrate opaque materials and create three-dimensional maps of materials by spectroscopic imaging non-destructively. Satisfactory results using model samples have been obtained by many institutions. In particular, the imaging by using THz pulses...
To achieve the Chu lower bound for the radiation Q, an electrically small magnetic dipole antenna should not store any magnetic energy internally to the minimum sphere enclosing the antenna. As shown in our previous works, the internal stored magnetic energy can be reduced, although not entirely eliminated, by introducing a solid magnetic core inside the antenna. In this paper, using analytical results...
In this paper we describe the design, key features and results obtained from the development of a generic platform usable for telemetry links and sensor network applications. Our target platform operates in the ISM band (433 MHz) and supports a variety of modulation and data handling options. The first part of the paper deals with design methodology, block organisation and some of the requirements...
Electronic calibration set for wideband sixport is discussed in the paper. The calibration method in use is mentioned, standard calibration sets are presented with their parameters and the electronic calibration set is designed to offer similar parameters with the ease of single connection to measurement system. Main circuit schematics with real measured values of S11 are shown and obtained results...
This paper is focused on the measuring method based on the sixport coupler. It is an alternative method usable in high frequency and microwave region. It has the main feature - rf part of measuring hardware is simple in comparison with conventional vector network analyzers. This paper describing an automatic sixport measuring system controlled by PC.
Reactive and radiative near-fields are important to be measured in connection with occupational human exposure. Both electric (E) and magnetic (H) field components need to be evaluated in this case and they are to be compared against the occupational safety limits. The need for a proper device and a correct procedure for these measurements are crucial. Present work focused on exposure assessment very...
The paper gives an overview of the phase of arrival (PoA) and time of arrival (ToA) techniques for distance measurement of UHF RFID tags. It introduces a new method based on the evaluation of received signal phase change during a linear frequency modulation (LFM) chirp. The phase of signal arrival is converted to the instantaneous frequency of a FMCW beat using a delay-multiply FSK demodulator with...
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