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We demonstrate coherent THz emission based on the stable operation of a dual-frequency vertical-external-cavity surface-emitting laser. The laser operates on two Laguerre-Gauss transverse modes in a single-axis cavity, thanks to sub-wavelength thick metallic transverse mask deposit on the surface emitting semiconductor structure. A beat note at frequencies from 50 GHz to 3 THz has been demonstrated...
The output power and tuning range of injection-seeded terahertz-wave parametric generators (is-TPG) have improved significantly in recent years. Peak output power of a few tens of kW have been achieved, and the upper limit of the tuning range has increased from 3.0 to 5.0 THz. However, the acquisition of spectra requires long measurement time, because is-TPG is a tunable source and emits only one...
In this paper, measurements with a THz imaging system at 346 GHz together with electromagnetic simulations have demonstrated the capability of THz sensing for the non-destructive density determination of intermediate products in the pharmaceutical industry. The results confirm the ability of THz imaging to detect density changes in pharmaceutical samples by measuring the phase variation of the wave...
We have been developing a nondestructive quantitative inspection technique for pharmaceutical tablets. We constructed a compact optical system to stabilize signal intensity, in which a galvano mirror was applied for adjusting incident angle of seeding beam and a 2D-CMOS sensor was used for signal detection. We evaluated its performance and confirmed that 0.5wt% of DL-histidine in L-histidine could...
Based on a number of inquiries from the industrial community Terasense has developed and started production of a new terahertz imaging system. The system is designed for a conveyor based non-destructive testing and security scanning applications. The imaging kit includes 1×256 pixel THz linear camera and 100 GHz (80 mW) source with a special projection optics. The terahertz imaging system has undergone...
This work explores a rapid design and manufacturing approach to realize complex 3D pillar type filter and transmission line structures for applications in the 220 GHz–325 GHz range, which cannot be economically reproduced by conventional machining processes or present rapid prototyping methods. The significance of this investigation is that at THz frequencies, the exact conductor shape and surface...
In this work the complete system for THz measurements is presented and briefly described. Proposed solution allows to avoid the most important disadvantages of the lock-in technique without compromising the noise parameters of the developed readout system. The prototype, designed and tested by the authors, supports the pixel line of FET-based THz detectors. The system consists of the hardware part...
We present two kinds of broadband terahertz wave modulator fabricated with large-area graphene-based field-effect transistors (GFET). One is with improved modulation depth and switch speed by cautiously selecting an ultrathin AbO3 film (60 nm) as the gate dielectric materials, which reduces the Coulomb impurity scattering and cavity effect, and thus greatly improves the modulation performance. Another...
This paper describes metal-oxide-semiconductor field effect transistors working as detectors of THz radiation integrated monolithically with a source follower (the common-drain amplifier). This solution makes lock-in measurements independent of the length of the connecting cable.
We introduce the use of Time-Frequency (TF) filtering applied to Terahertz Time-Domain Spectroscopy (THz-TDS) data in order to extract valuable information hidden into the noise floor. The Short Time Fourier Transform (STFT) provides a spectrum analysis in time, we optimized its Gaussian window in order to analyse and filter the THz signals of substances. The formalism presented allows an efficient...
We report on a detector-free on-chip dual frequency comb setup based on terahertz quantum cascade lasers. The presented dual-comb covers a bandwidth of 630 GHz with a centre frequency of 2.5 THz. Instead of a fast detector one of the lasers has been used as a fast detector itself. The frequency comb spacing was analysed using frequency counting techniques revealing an accuracy down to δfrep/fcarrier...
Automotive coating plays an important role in car industry. They protect the car bodies from various aggressive weathering and mechanical deformations. Though many techniques have been developed for car coating, there is still a demand for non-destructive characterization of multilayer coatings. Therefore, research on new measurement methods is still ongoing. In this paper, we investigate thin coating...
We report thermal effects on carrier dynamics in graphene revealed by terahertz spectroscopy. We attribute our observations to extreme sensitivity of carrier density and mobility to environmental changes.
Maximising the power extracted from UTC photodiodes is central to the successful realisation of photonic terahertz emitters. For antenna integrated UTCs this requires the optimisation of the impedance match between UTCs and antennas. We present a comprehensive investigation of the UTC output impedance up to 400 GHz, by means of a semi-analytical approach and using 3D full-wave modelling. We introduce...
We present non-contact characterization of GaAs Schottky contacts in the 140–220 GHz band. The non-contact probing technique utilizes planar on-chip antennas that are monolithically integrated with the coplanar waveguide environment housing the Schottky diode under test. The diode contact is fabricated through a 6 mask lithographic process with a 5 μm deep-trench under the contact to minimize parasitics...
A new approach for precise complex optical parameter of highly absorptive liquid is proposed for transmission THz time-domain spectroscopy. Due to the nature of liquid, indirect measurement of sample thickness increases inaccuracy in optical parameter. Here, we reduced uncertainty in optical parameter through an algorithm optimizing sample thickness by Kramers-Kronig relations. Less than 2% error...
We investigate the impact of periodic sampling time errors of terahertz time-domain waveforms and analytically calculate the influence on the spectrum of the measurement. We assess the effects on optical parameter extraction.
We present a compact, room-temperature, high-power and broadly tunable terahertz source based on a two-section digital distributed feedback laser diode and a plasmonic photomixer. It offers a 3 THz radiation frequency tuning range with a radiation power of 0.45 mW at 1.62 THz.
We demonstrate a parallel-plate waveguide (PPWG) T-junction used as a power splitting router. We are able to direct the THz light down either one of the two output channels by integrating a small triangular septum into the waveguide plate. We find good agreement between experiment and simulation in both amplitude and phase. We show that the ratio between waveguide outputs varies exponentially with...
We devise arrays of surface emitting THz QCLs exploiting two novel lithographic configurations: a) a dual periodicity slit architecture and b) corrugated sinusoidal wire laser cavities. Extremely low divergent optical beams, with up to 85 mW of emitted optical powers and 245 mV/A slope efficiencies have been reached.
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