Abstract-Hyperspectral terahertz imaging with electro-optic dual combs and a FET-based detector

Pedro Martín-Mateos, Dovilė Čibiraitė-Lukenskienė, Roberto Barreiro, Cristina de Dios, Alvydas Lisauskas, Viktor Krozer,  Pablo Acedo

https://www.nature.com/articles/s41598-020-71258-6

In this paper, a terahertz hyperspectral imaging architecture based on an electro-optic terahertz dual-comb source is presented and demonstrated. In contrast to single frequency sources, this multi-heterodyne system allows for the characterization of the whole spectral response of the sample in parallel for all the frequency points along the spectral range of the system. This hence provides rapid, highly consistent results and minimizes measurement artifacts. The terahertz illumination signal can be tailored (in spectral coverage and resolution) with high flexibility to meet the requirements of any particular application or experimental scenario while maximizing the signal-to-noise ratio of the measurement. Besides this, the system provides absolute frequency accuracy and a very high coherence that allows for direct signal detection without inter-comb synchronization mechanisms, adaptive acquisition, or post-processing. Using a field-effect transistor-based terahertz resonant 300 GHz detector and the raster-scanning method we demonstrate the two-dimensional hyperspectral imaging of samples of different kinds to illustrate the remarkable capabilities of this innovative architecture. A proof-of-concept demonstration has been performed in which tree leaves and a complex plastic fragment have been analyzed in the 300 GHz range with a frequency resolution of 10 GHz.

Abstract-Terahertz Detection With a Low-Cost Packaged GaAs High-Electron-Mobility Transistor

Elham Javadi,  Alvydas Lisauskas,  Mahmoud Shahabadi,  Nasser Masoumi , Jingshui Zhang, 
Johann Wolfgang Goethe

https://ieeexplore.ieee.org/document/8506393

We present experimental results of an investigation into the performance of a commercial, packaged GaAs high-electron-mobility transistor (HEMT) as a detector of terahertz (THz) radiation in the frequency ranges 0.22–0.32 and 0.520–0.650 THz. Enclosed in a standard ceramic housing and without a dedicated antenna for radiation coupling, the transistor is capable of sensitive direct detection (power detection) of THz radiation at room temperature. The device responsivity shows a strong variation with wavelength, indicating that various device features (transistor metallization, contact pads, wires) act as an effective THz antenna. With the THz radiation focused with a parabolic mirror (and without a substrate lens), the maximum responsivity reaches 2.5 and 0.72 V/W with values of the minimum optical noise-equivalent power (NEP) of 1.4 and 2.5 nW/ Hz−−−√ at the sensitivity peaks at 0.271 and 0.632 THz, respectively. The performance of the HEMT, in comparison with antenna-coupled FET detectors optimized for THz detection (TeraFETs), can be assessed better if the responsivity and the NEP are referred to the effective antenna cross-section determined experimentally for the device. We arrive at a cross-sectional responsivity of 42 V/W (1.6 V/W) and a cross-sectional NEP of 135 pW/ Hz−−−√ (1250  pW/ Hz−−−√ ) at 0.271 THz (0.632 THz), for measurements through the ceramic cap. The cross-sectional NEP values are about one order of magnitude at 0.271 THz and two orders of magnitude at 0.632 THz higher than those achieved with the best TeraFETs, yet in a range where they enable many practical applications at low cost for the detector.

Abstract-Efficient Detection of 3 THz Radiation from Quantum Cascade Laser Using Silicon CMOS Detectors

Kęstutis Ikamas, Alvydas Lisauskas, Sebastian Boppel, Qing Hu, Hartmut G. Roskos

https://link.springer.com/article/10.1007/s10762-017-0407-9

In this paper, we report on efficient detection of the radiation emitted by a THz quantum cascade laser (QCL) using an antenna-coupled field effect transistor (TeraFET). In the limiting case when all radiated power would be collected, the investigated TeraFET can show up to 230 V/W responsivity with the noise equivalent power being as low as 85 pW/Hz−−−√$\sqrt{\text{Hz}}$ at 3.1 THz, which is several times lower than that of the typical Golay cell. A combination of the QCL and a set of off-axis parabolic mirrors with 3-inch and 2-inch focal lengths was used to measure the signal-to-noise ratio (SNR) of the TeraFET. The practically achieved SNR was five times lower than that of the Golay cell and two orders of magnitude lower than a bolometer’s. However, TeraFETs are much faster and do not need a signal modulation, thus can be used both in a continuous mode for power monitoring or for investigation of transient processes on a sub-microsecond time scale.

Abstract-Exploration of Terahertz Imaging with Silicon MOSFETs

• Alvydas Lisauskas, 
• Maris Bauer, 
• Sebastian Boppel, 
• Martin Mundt, 
• Bassam Khamaisi, 
• Eran Socher,
• Rimvydas Venckevičius, 
• Linas Minkevičius, 
• Irmantas Kašalynas, 
• Dalius Seliuta, 
• Gintaras Valušis, 
• Viktor Krozer, 
• Hartmut G. Roskos, 

• http://link.springer.com/article/10.1007%2Fs10762-013-0047-7

We summarize three lines of development and investigation of foundry-processed patch-antenna-coupled Si MOSFETs as detectors of THz radiation: (i) Exploiting the pinciple of plasma-waved-based mixing in the two-dimensional electron gas of the transistors’ channels, we demonstrate efficient detection at frequencies as high as 9 THz, much above the transit-time-limited cut-off frequencies of the devices (tens of GHz). Real-time imaging at 600 GHz with a 12 × 12 detector array is explored. (ii) Given the limited THz power usually available for applications, we explore imaging with enhanced sensitivity in heterodyne mode. We show that real-time operation of a 100 × 100-pixel heterodyne camera should be possible at 600 GHz with a better dynamic range (30 dB) than for direct power detection (20 dB), even if only a quarter-milliwatt of local-oscillator power, distributed radiatively over all detector pixels, is available. (iii) Finally, we present an all-electronic raster-scan imaging system for 220 GHz entirely based on CMOS devices, combining the CMOS detectors with an emitter circuit implemented in a 90-nm CMOS process and delivering radiation with a power on the 100- μW scale. Considering progress in the field, we anticipate that the emitter concept of oscillator-based power generation with on-chip frequency multiplication will carry well into the sub-millimeter-wave regime.