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We report on unusual photoconductivity under the action of strong terahertz laser pulses in PbTe(Ga). The character and even the sign on the photoconductivity depends on the level of photoexcitation: it is positive and persistent at high degrees of excitation, whereas it is negative and non-persistent at low levels of excitation. We show that this non-trivial photoelectric behaviour is due to formation...
We present an approach for two-port on-wafer calibration to establish the test reference planes within the substrate of the device under test for the WR3 (220–325 GHz) and WR5 (140–220 GHz) frequency bands. On-wafer calibration is useful for characterizing elements such as transistors for modeling or for the confirmation of circuit models. There are numerous publications for on-wafer calibrations,...
We report on the observation of Kerr effect induced by an intense terahertz pulse in a (100) Gallium Phosphide crystal. The temporal and angular behaviors of the phase retardation have been measured and agree well with theoretical predictions. From these measurements, we extracted the nonzero tensor elements of the third-order response function of the crystal in the terahertz range.
A practical solution using a THz optical source as a Local Oscillator (LO) for radio astronomy above 2 THz requires that the source to be frequency or phase locked. Therefore, it is crucial to enable a high conversion efficiency heterodyne mixer to produce a stable LO source that can operate at room temperature. Harmonically pumped 1.9–3.2 THz Schottky diode based mixers have been designed to enable...
A compact 140GHz 8-way power combing module is described using compositing integrated structure. For a unit of radial power combing, the width of the module subjects to severe limitations. We develop a step-by-step design procedure, including waveguide T-junction, hybrid based on waveguide directional coupler and distorted T-junction. For purpose of improving the gain of the module, a driving amplifier...
We report nonlinear terahertz transmission through photoexcited graphene using optical-pump/terahertz-probe technique. Transient enhancement in the terahertz transmission of the graphene sample is observed when the sample is photoexcited. This transmission enhancement is found to decrease nonlinearly with the terahertz electric field.
A simple method is presented to characterize the dielectric probe for the near-field beam scanning in mm-wave domain. It is shown that the probe spatial-response can be modeled by Gaussian functions and then directly used in the convolution process to determine the actual measured field. Therefore, the complicated classic deconvolution operation can be replaced by an easy comprehensive analytical...
This paper presents the design, fabrication and characterization of a terahertz (THz) spoof surface plasmon based near field probe. It is built using a single side metalized bulls-eye plastic structure with a micro-lens at the aperture. 3-D printing is used in the fabrication of the plastic structure followed by a thin film metal coating. Details analysis is carried out using FEM simulation tool....
We report the first investigation of single Titanium Dioxide (TiO2) sub-wavelength size (20–30μm) spheres and ellipsoids using THz near-field microscopy. The Mie resonances are observed in individual particles allowing characterization of the resonance line-width and its dependence on the particle dimensions and shape.
A portable THz imaging system for the study of wall paintings is currently under construction in the framework of the THz-ARTE project. The device design and operating principle will be presented together with preliminary results on test samples.
We report on the second harmonic generation of a near-infrared pulse in a Zinc Telluride (ZnTe) crystal through the Pockels effect induced by an intense terahertz pulse, demonstrating cascading second-order nonlinear phenomena in the terahertz range.
We investigate through numerical simulation the coupling properties of a novel, AC-coupled, contact-free probe. The new probe couples radiation from a CPW-embedded device-under-test via polarization current, which is then transformed to conduction current in the probe and down-converted in frequency to baseband by an optically-pumped photomixer. Numerous simulations have been realized in order to...
Photo-excited charge carriers at semiconductor surfaces generate pulses of terahertz (THz) radiation. By mapping the spatial distribution of the THz radiation in the near-field and the angular emission pattern in the far-field, we link the THz generation process to the photo-current direction. We find that inplane carrier dynamics play an important role and can even be the dominant source of THz radiation.
Ocular temperatures during infrared or millimeter wave exposure were measured with thermography, fluoroptic thermometer, and microencapsulated thermochromic liquid crystals (MTLC) method. MTLC showed good correlation with ocular damage.
This paper reports the design, fabrication, and characterization of a suite of dielectric probes for near-field and evanescent microfluidic sensing applications. Four different probe designs are studied. These structures are made from cylindrical alumina dielectric rods, and were integrated with microfluidic channels. Mixtures of two different solvents were used to characterize the probes. The sensitivity...
Interpretation of the vector waveform detected by using the electro-optic (EO) sampling method in the terahertz time-domain spectroscopy is presented, especially when there is a velocity difference between the elliptically-polarized terahertz pulse and the optical probe pulse in the EO crystal. The formulation can be used to interpret the time-domain vector waveform detected by the EO sampling method...
The recent development of micromachined probes for on-wafer characterization of devices and circuits now permit measurements to the WR-1.0 waveguide band (0.75–1.1 THz). This paper presents the probe design concept, describes methods for characterizing the probes, and applies the probes for direct on-wafer characterization of planar Schottky diodes at 1 THz. Measurements show the WR-1.0 probes exhibit...
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