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Chip scale terahertz dielectric waveguides, consisting out of high resistivity silicon as a core material have been fabricated. The waveguide loss is measured to be ∼1dB/cm at both 1 THz and 2.5 THz.
Millimetre wave radar has been successfully applied in cloud research for a number of decades. The Rutherford Appleton Laboratory (RAL) has developed a 94 GHz radar based on solid state components and operated in Frequency Modulated Continuous Wave (FMCW) mode. The approach for improving the RF design — including the implementation of Doppler capability — and the results of this activity will be presented.
A fully integrated THz detection system consisting of an on chip dipole antenna, a plasmonic detector, and a wide band amplifier in 130 nm AlGaAs/InGaAs pHEMT technology is reported. The fabricated chip achieves an absolute responsivity of 3 V/W, while maintaining a 50 dB signal to noise ratio (SNR) over a modulation bandwidth of 8.5 GHz at ∼ 0.3 THz.
A 19×8 pixel array with a read-out integrated circuit was designed and fabricated in a micro-machined SOI-CMOS process. The pixels are antenna-coupled MOSFET bolometers operating at room temperature in a wide 0.6–1.2 THz band. The read-out circuit features column multiplexed differential amplifiers, offset calibration capability and chopper stabilization. We present the performance of the read-out...
Design development of continuous-wave 240 GHz gyrotron and 300 GHz gyrotrons with output power about 200–1000 kW for fusion research at advanced plasmas with intense magnetic field is presented. Main goal of such gyrotrons is application for EC complexes of IGNITOR and DEMO tokamaks. This paper includes task motivation and existing technical basis, results of calculation, design, technical requirements...
We demonstrate the generation of 11ps terahertz pulses from metal-metal (MM) quantum cascade lasers (QCLs) at 77K via active mode-locking. Contrary to popular belief that a long gain recovery time is required, we demonstrate that the dominant factor necessary for active pulse generation is in fact the synchronization between the propagating electronic microwave modulation and the generated THz pulses...
A hybrid mode section is integrated into the end of the metal-metal (MM) waveguide of a terahertz (THz) frequency quantum cascade laser (QCL) by removing sub-wavelength portions of the top metal layer. This allows a hybrid mode to penetrate into the air, which reduces the effective index of the mode and improves the out-coupling performance at the facet. The transmission of the processed metal-metal...
In this paper preliminary results of radar imaging measurements using a narrowband signal in the low terahertz band are presented. Measurement system architecture as well as the narrowband imaging technique are also discussed. Verification of the theoretical method of acquiring images by the use of narrowband signal through its application to real radar data is presented. Additionally, the results...
Shallow donor impurities in silicon, once frozen out at low temperature, share many properties in common with free hydrogen atoms [1]. They have long been the subject of spectroscopic investigation, but it is only very recently [2,3] that it has been possible to investigate the time-domain dynamics of orbital excitations such as the 1s to 2p, due to the difficulty of obtaining short, intense pulses...
Spatial light modulators (SLM) can be used for many applications, including imaging and beam steering. With the emergence of THz SLMs being able to control thousands of pixels, the aforementioned applications become feasible for the THz region. The degree of control that can be exerted with a SLM and in turn its usefulness directly depends on the light pattern it creates. The resulting light patterns...
We demonstrate a terahertz imaging system utilizing self-mixing in a 2.9 THz quantum cascade amplifier, through the use of an anti-reflection coated silicon lens to completely suppress lasing action. The fully exploited optical gain of the quantum cascade amplifier allows induced voltage perturbations to be spatially mapped with a signal to noise ratio of up to 55 dB and an acquisition rate of up...
We have demonstrated phase sensitive detectors of coherent terahertz radiation that use single nanowires as active elements. The single GaAs/AlGaAs nanowires acted as sensitive photoconductive elements within a gold antenna structure on quartz. The detectors were also implemented in a terahertz time domain spectroscopy (THz-TDS) system. Our devices show great promise as near-field terahertz sensors...
The frequency of a 2.5 THz QCL are stabilized to sub-hertz accuracy by phase-locking to a stable 100 MHz microwave reference, using a 2.3–3.2 THz room temperature Schottky diode based harmonic mixer. The down-converted phase locked beat note is stable over a long term test.
Terahertz (THz) spectroscopy has emerged over the last two decades as a versatile probe of a large variety of materials and processes. Because the transient THz electric field rather than its power is measured, frequency-dependent material properties such as absorption coefficient, refractive index, and complex conductivity in the far-infrared region of the electromagnetic spectrum are determined...
Beam profile measurement of broadband THz pulses in a TDS system are carried out by analyzing the spatial distribution of the pulse. Beam-waists of different frequency components are calculated. Overall the waist decreases with the increasing frequency with higher order modes being observed.
A method of reducing the dielectric loss of poly-dimethylsiloxane (PDMS) in the terahertz range with dopants is presented. Samples of PDMS are doped with varied concentrations of polytetrafluoroethylene (PTFE) micro-particles, and characterized with terahertz time domain spectroscopy (THz-TDS) in order to extract their material properties. It is found that controlled doping can significantly reduce...
We demonstrate a spatially resolved method to measure carrier lifetimes and carrier distributions based on optical pump — terahertz probe spectroscopy. The pump-probe delay range spans from 600 ps to 200 μs. The spatial resolution is sub-wavelength being better than 50 μm (≺ λcenter/6 at 1THz).
THz mixtenna chips and quasi-optical mixers for focal plane imaging applications are presented. Firstly, the THz Schottky diodes with the cutoff frequency of 3.2 THz are designed and fabricated. Then, the mixtenna chips are designed, by extending the two pads of the diode to a differentially-fed antenna. Finally, the 325 GHz quasi-optical mixer and mixer array, which consist of the mixtenna chip integrated...
It is demonstrated that the thermal origin of the excess wing in the THz portion of the dielectric spectrum of water is the same as that of the main dielectric peak. The implication is that models positing the free rotation of water molecules to account for the Excess wing are not correct. A self-terminating Proton cascade is one possible explanation.
The design and the performance of a 4.7-THz local oscillator (LO) for the GREAT (German REceiver for Astronomy at Terahertz frequencies) heterodyne spectrometer on SOFIA, the Stratospheric Observatory for Infrared Astronomy, are presented. The LO is based on a quantum-cascade laser, which is mounted in a compact mechanical cryocooler. It delivers up to 150 μW output power into a nearly Gaussian shaped...
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