This PDF file contains the front matter associated with SPIE Proceedings Volume 11124 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Although unique potentials of terahertz waves for chemical identification and material characterization have been recognized for quite a while, the relatively poor performance of current terahertz spectroscopy and spectrometry systems continue to impede their deployment in field settings. This talk describes some of the recent advancements in terahertz spectroscopy systems by using optically-pumped plasmonic photoconductors for terahertz wave generation and detection. Incorporating plasmonic nanostructures inside the active area of photoconductive terahertz sources and detectors offers enhanced quantum efficiencies while maintaining ultrafast operation. This enhancement is due to the unique capability of plasmonic nanostructures to significantly increase the concentration of photo-induced carriers inside the device active area, where they interact with a bias/terahertz electric field to generate/detect terahertz radiation. By the use of this powerful technique, broadband terahertz spectroscopy with record-high signal-to-noise ratio levels exceeding 140 dB and broadband terahertz spectrometry with quantum-level sensitivities are demonstrated. Such high-sensitivity terahertz spectroscopy and spectrometry systems could offer numerous opportunities for e.g., biomedical sensing, atmospheric studies, astrophysics studies, pharmaceutical quality control, and security screening applications.

The quantum cascade laser (QCL) has been central to the development of terahertz (THz) science and technology in the last decade, thanks to its electronic and optical properties, which can be accurately tailored with quantum and photonic engineering. Control over the spatial and spectral features of THz QCL radiation has been addressed with different solutions, exploiting periodic structures such as edge-emitting 3rd-order distributed feedback lasers, plasmonic lasers, and one dimensional (1D) or two-dimensional (2D) photonic crystals. Novel resonators exploiting aperiodic photonic architectures recently emerged as a versatile approach to engineer the emission of THz QCLs, circumventing the power extraction issues of periodic resonators. Here, we report on the development of 1D and 2D THz QCL resonators providing a combination of high output power, controlled beam shaping and stable continuous wave (CW) operation. We devised a laterally corrugated wire laser with a top extraction hole array. The distinct periodicities of the lateral corrugation and the top hole array allow separate control of light feedback and extraction, optimizing the power output (42 mW in pulsed regime), slope efficiency (250 mW/A) and beam divergence (10°). Stable single-mode emission was achieved with a maximum CW power output of 6 mW. We furthermore demonstrate the first electrically pumped CW random THz lasers reaching a maximum peak power of 21 mW and a CW power of 1.7 mW with multimode emission over a 430 GHz-bandwidth. Using an external coupled cavity, a continuous tuning of 11 GHz and of 20 GHz with modehopping were demonstrated.

Current-injection pumping in graphene makes carrier population inversion enabling lasing and/or amplification of terahertz (THz) radiation. We have recently demonstrated single-mode THz lasing at 100K in graphene-channel transistor laser structures. Introduction of a gated double-graphene-layered (G-DGL) van der Waals heterostructure is a promising route to further increase the operation temperature and radiation intensity via plasmon- and/or photon-assisted quantummechanical tunneling. We have proposed a cascading of the G-DGL unit element working as a new type of THz quantumcascade lasers. Numerical analyses demonstrate further increase of the quantum efficiency of THz lasing by orders of magnitude compared to a transistor or single G-DGL structure.

Frequency combs, spectra of phase-coherent equidistant lines, have revolutionized time and frequency metrology. The recently developed quantum cascade laser (QCL) comb has exhibits great potential with high power and broadband spectrum. However, in the terahertz (THz) range, cryogenic cooling has to be applied for THz QCL combs. We report a room temperature THz frequency comb at 3.0 THz based on difference-frequency generation from a mid-IR QCL comb. A largely detuned distributed-feedback grating is integrated into the QCL cavity to provide the single mode operation as well as enhanced spatial hole-burning effect for multimode comb operation. Multiheterodyne spectroscopy with multiple equally spaced lines by beating it with a reference Fabry-Pérot comb confirms the THz comb operation. This type of THz comb provides a new solution to chip-based high-speed high-resolution THz spectroscopy with compact size at room temperature.

Incoherent terahertz (THz) sources can be compact, stable, reliable and cheaper alternative to coherent emitters for compact THz systems. Low power of incoherent THz emitters can be compensated by benefit from extremely high sensitivity of THz micro-detectors. Incoherent THz torch device based on Ga(As,Bi)/AlGaAs parabolic quantum well (PQW) is modeled, fabricated and experimentally investigated paying special attention to the THz spectral range and optical properties. The structures for optical characterization were grown using MBE technique on GaAs substrates. The experimental study was carried out to measure the absorption by intersubband transition of electrons in PQW using vacuum Fourier transform spectroscopy, conventional farinfrared Fourier transform spectroscopy and THz time-domain spectroscopy. Transmittance spectra dependence on temperature and photo-excitation of undoped structures for THz torch device is studied exploring impact of the PQW on THz spectra.

Plasma-based generation schemes of terahertz (THz) are promising and flexible sources of high-field, broadband THz pulses. The traditional plasma-generation scheme involves combining an ultrafast laser pulse with its second harmonic in a tight focus to generate a plasma from which THz radiation is emitted. We demonstrate non-traditional experimental schemes for plasma-based THz generation using multiple laser pulses. THz emission of a plasma formed by a commensurate two-color pulse (containing a near IR frequency and its second harmonic) can be enhanced by the addition of an 800-nm pulse, which is the waste light from an optical parametric amplifier. We observed enhancements of the THz electric field by a factor of up to 30. Numerical calculations done using the well-known photocurrent model are in good agreement with experimental results. These studies help suggest future avenues of improvement in practical table-top plasma generation of THz.

This proceeding details the experimental investigation and scheme used to generate vortex beams at THz and far-infrared frequencies. Main experimental and numrical results are presented by M. Ivanov et al.^{1, 2} We investigate the generation of broadband terahertz (THz) pulses between 10 and 40 THz with a phase singularity from two-color femtosecond laser-induced gas-plasmas. Experimental scheme allows for independent control of the amplitude, phase, polarization, and longitudinal and transverse positions of fundamental and second harmonics. When the second harmonic beam has a vortex charge the THz beam acquires an azimuthal phase modulation as well. Moreover, it turns out that also the THz intensity becomes modulated along the azimuthal angle. The phase structure of the singular THz beam is indirectly revealed by astigmatic transformation of the beam by a cylindrical mirror and additionally confirmed by the vortex THz beam behaviour upon change of relative phase between the fundamental and the second harmonic.

TeraFERMI is a beamline built up in 2015 at the Free Electron Laser (FEL) Fermi at Elettra in Trieste (Italy). Fermi is a seeded FEL that works in a single pass-single bunch mode at 10 or 50 Hz, covering the spectral range from 100 to 4 nm. TeraFERMI is based on a Coherent Transition Radiation source that provides high intense THz electric field in the MV/cm range. Such a THz electric field can push nonlinear materials well into their nonlinear regime. The beamline experimental setup fulfills the capability to address nonlinear regime by measuring both fluence-dependent transmission/reflection spectra and pump-probe response. A class of materials particularly studied at TeraFERMI is that of Topological Insulators. Indeed, thanks to their Dirac massless carriers of their conductive surface, topological insulators show nonlinear THz behavior similar to the case of graphene.

The use of photo-mixing techniques for THz emission offers attractive performances such as tunability and modulation bandwidth, that are suitable for bio-medical sensing and imaging, communications, or security. We will present the state-of-the-art performances of a vertical-external-cavity surface-emitting laser that operates on two transverse modes to ensure a stable continuous-wave and coherent (longitudinal, transverse and polarization) dual-frequency operation. THz emission is subsequently obtained by excitation of an uni-traveling-carrier photodiode (UTC-PD). The stability of the dual-frequency operation is achieved thanks to different types of functionalized surfaces involving the micro-fabrication of integrated III-V absorbing metallic masks or metamaterial phase masks by e-beam lithography. These functionalized surfaces allow to shape the optical and THz performances in terms of power, tunability and coherence. The latter will be specifically detailed in terms of longitudinal coherence, showing a THz frequency noise that is orders of magnitude lower than the optical one thanks to a significant correlation of technical noise. Tunable emission will be demonstrated from 50 GHz up to few THz with a linewidth of 150 kHz (during 3-ms), for a power of 1 W at 260 GHz that is limited by the UTC-PD for an optical excitation at 1064 nm at room temperature. We will discuss on the possibility to improve such a power significantly by taking advantage of the involved high-order transverse mode, offering possible intrinsically coherent networks of photo-emitters, thus paving the way to compact and agile coherent THz sources offering an output power over few mWs at frequencies of 100s of GHz.

A continuous wave (CW) terahertz source emitting in a broad frequency range (1-5THz) is promising towards achieving a compact, high power, finely tunable, room temperature terahertz generation system which will be of immense significance towards the realisation of terahertz applications in spectroscopy, communication, sensing, and imaging among others. We have demonstrated a tunable continuous-wave Quantum Dot external cavity laser emitting at two frequencies for continuous wave terahertz emission in a Quantum dot Photoconductive Antenna (PCA). The external cavity QD Laser has been characterised with tunability of 152nm and a tuning range from 1143nm -1295.8nm that lies within the THz difference frequency for the generation of THz radiation from QD based PCAs.

In this presentation we will demonstrate a highly efficient generation of higher-order THz harmonics in graphene. The underlying physics is the collective, thermal response of the free electrons in graphene to the driving THz fields. As a result, graphene possesses the nonlinear coefficients several order of magnitude higher than other typical solids.

Ultrashort terahertz (THz) pulses are a powerful tool for both probing and controlling novel phenomena in quantum materials. This is particularly useful in Dirac materials, since these materials exhibit novel magnetic and lattice excitations that can potentially be used to control their properties. Here, the use of ultrashort THz pulses to reveal the circular photogalvanic effect in the Weyl semimetal TaAs and probe magnetoplasmon modes in graphene nanoribbons will be examined. We performed THz emission spectroscopy on the (112) and (001) surfaces of the Weyl semimetal TaAs. Our data enables us to clearly distinguish between helicity-dependent photocurrents generated within the ab-plane and polarization-independent photocurrents flowing along the non-centrosymmetric c-axis. Such findings are in excellent agreement with previous static photocurrent measurements. However, by considering both the physical constraints imposed by symmetry and the temporal dynamics intrinsic to current generation and decay, we can attribute these transient photocurrents to the underlying crystal symmetry of these materials. We also used terahertz (THz) magneto-optical spectroscopy to demonstrate how a periodic array of graphene micro-ribbons can be used to control the transmission spectrum and polarization state of a THz pulse whose electric field is oriented along the pattern’s axis of periodicity (perpendicular to the long axis of the ribbons). Our results demonstrate that graphene micro-ribbon arrays are a powerful system for controlling the coupling between light and magnetoplasmonic modes. This enables the tailoring of THz transmission profiles and polarization states using applied magnetic fields.

We provide an overview on THz frequency metrology, starting from the nowadays available continuous wave THz sources, discussing their main features such as tunability, spectral purity and possibility of frequency referencing to the primary frequency standard. A comparison on the achieved results in high precision molecular spectroscopy is given and discussed, and finally a special emphasis is placed on the future developments of this upcoming field. In fact, particular attention will be given to new generation metrological-grade THz sources, such as a novel 3-octaves-spanning roomtemperature continuous-wave source based on difference frequency generation, and the latest developments regarding quantum cascade laser frequency combs based on four-wave-mixing nonlinear processes.

Coherently excited phonons are unique tools to control material properties, drive phase transitions or even access hidden phases on ultrafast time scales. The increasing availability of high-field THz and mid-infrared sources facilitates targeting of specific resonantly driven phonon modes, while leaving the material in its electronic ground state. Nevertheless, this direct excitation is restricted to IR-active modes, whereas purely Ramanactive modes are symmetry protected against even intense resonant THz fields. Thus, for Raman-active modes, nonlinear excitation mechanisms must be employed, which are either mediated through modulation of the electric polarizability or through anharmonicities of the crystal lattice. Respectively, these difference-frequency processes are conventional impulsive stimulated Raman scattering (ISRS) and, more recently, ionic Raman scattering (IRS), which both lack the precise selectivity of resonant excitation. Here, we present the THz sum-frequency counterparts of these two mechanisms, which are more selective, nonimpulsive, and provide direct control over the phonon phase. We demonstrate THz sum-frequency excitation of the archetypal Raman-active phonon in diamond. This two-photon absorption process, the upconversion counter part of ISRS, directly imprints the carrier-envelope phase of the light field onto the coherent phonon’s phase. Additionally, our theoretical formalism based on first-principles calculations in combination with phenomenological modeling predicts an efficient sum-frequency counterpart for IRS, which was subsequently confirmed by other experimental research groups. In summary, we complete the map of photonic and ionic Raman excitation mechanisms with their sumfrequency counterparts, providing a comprehensive guide for selective excitation of coherent phonons and other Raman-active modes by strong THz fields.

The past decade has seen transformative changes in the terahertz spectrum beyond 100 GHz, both in terms of technological progress and in application development. Of note is the progress made towards enabling efficient and compact Terahertz systems operable at room temperature and deployable at large scales. On the application development, the interest in this spectrum has grown significantly in the band due to the evolution of 5G and steadily increasing large-scale deployments of technology in the sister millimeter-Wave bands. On the technology side, we have seen significant advancements in a multitude of integrated technology substrates in electronics, photonics and in hybrid systems. In the electronics regime, this potpourri of technology has spanned from III-V based devices such as InP HBTs and HEMTs (f_max > 1 THz) to silicon-based IC technology that have shown remarkable advancements in complex systems including chip-scale phased arrays, active and passive imagers, and wireless communication systems. The ‘THz gap’ has steadily been closing in the past ten years due to the technological progress, and attention is being paid now towards closing the ‘THz’ and large-scale ‘application’ gap in the next decade. To enable this shift in paradigm in presence of device limitations, we will need to innovate on new design architectures that allow properties such as reconfigurability, adaptability and multi-functionality in THz chip-scale systems yet being realized in substrates where the devices are inherently not optimally efficient. In this paper, we summarize the advancements in integrated THz systems in the past decade, discuss future challenges and directions to progress towards that goal.

We present a self-mixing terahertz-frequency gas spectroscopy technique using a multimode quantum cascade laser. A precision-micro-machined external waveguide module and a double-metal quantum cascade laser device are used to increase the optical feedback and the laser’s frequency tuning range. Methanol spectra are obtained using two laser modes at 3.362 THz and 3.428 THz simultaneously, with more than 8 absorption peaks resolved over a 17-GHz bandwidth, which provide minimum detectable absorption coefficients of 2.7×10^-4 cm⁻¹ and 4.9×10⁻⁴ cm⁻¹, respectively. In contrast to all previous self-mixing spectroscopy, our multimode technique expands the sensing bandwidth significantly. This broadband spectroscopy technique can potentially be used for the identification and analysis of chemical, biological radiological and nuclear (CBRN) agents and explosives.

In a topological crystalline insulator such as Pb_1-xSn_xSe, massless Dirac states emerge at an interface with a trivial insulator. We demonstrate the great versatility of Pb_1-xSn_xSe electronic properties, which makes it a highly promising material to control the massless Dirac states emerging from topological properties. Using magnetooptical transmission spectroscopy on high quality molecular beam epitaxy grown Pb_1-xSn_xSe, we probe the variation of its bulk energy gap versus chemical composition, temperature, and strain. The determination of its bulk electronic properties will be of critical relevance to design heterostructures. A magneto-optical study on PbSnSe/PbEuSe superlattices will allow us to characterize the topological interface states occurring at each interface, as well as their tunability versus temperature. The engineering of these massless states is shown to be a promising route to achieve photo detection and photoemission in the terahertz range.

Based on parallel-plate waveguides (PWWGs), we have developed both passive and active terahertz (THz) sensors, filters, splitters, and switches. We utilize the PPWG since it has excellent waveguiding properties with a simple geometry that allows for incorporation of unique electromagnetic functionalities. A few passive devices are discussed while the focus remains on active devices. The active control is enabled by our innovation to incorporate liquid metals, which can be relocated by application of a small electrical voltage (< 4V), as part of the waveguide geometry itself. The device geometry directly affects the device performance (e.g., frequency band of operation, channel output power). Therefore, by moving the liquid metal, the geometry is reconfigured which results in altering the device function. To show the practicality of these devices to be used for THz wireless communications, we demonstrate the ability of these devices to support a 1 Gb/s data stream on a THz carrier wave and show that this signal can be successfully switched with high modulation depths of ±40 dB. These results show the strong promise of these components to form important signal processing building blocks in the future infrastructure of THz wireless communications.

One can observe terahertz (THz) radiation from various kinds of materials, when excited with a femtosecond laser. The observation of the THz waveforms enables us to explore ultrafast nature of electronic materials and devices as THz emission spectroscopy. When one excites the THz emission from a certain substance with the laser and visualizes the emission images by scanning the laser beam on it, the resolution of the images is limited by the laser beam diameter rather than THz wavelength. Thus, construction of a laser-THz emission microscope (LTEM) would provide a new tool for material/device science and industrial applications. We proposed and have been developing LTEM since 1996 and evaluated various materials and devices such as high-Tc superconductors, manganites, ferroelectrics, wide gap semiconductors, and VLSIs. Here we present recent progress on the study focusing on semiconductor industry application. the noncontact local evaluation of m-plane GaN wafers, deep-inside of multi-junction solar cells, failures in VLSIs, and the surface potential of passivated Si wafers will be introduced.

Several terahertz-wave radar techniques based on a resonant-tunneling-diode (RTD) oscillator are under investigation. First, an amplitude-modulated continuous-wave (AMCW) radar able to measure the absolute distance was achieved by demodulating the wave returning from the target and measuring its phase, either by determining the time delay with an oscilloscope, or by using an IQ demodulator to determine the sine and cosine of the phase. Our current record with this type of radar is a ranging error of 0.063 mm; however, it can only measure the distance up to a single reflecting surface. Second, a subcarrier frequency-modulated continuous-wave (FMCW) radar has been demonstrated to work and is expected to allow the simultaneous ranging of several targets. The ranging error for this radar was found to be 0.73 mm. Additionally, a radar technique based on the swept source optical coherence tomography (SS-OCT) principle is proposed. Terahertz-wave 2D imaging can be combined with these radar techniques to obtain a 3D imaging system.

We present a terahertz-SLM with a frequency working range from 1.0 THz to 2.3 THz. Over the complete frequency range, the spatial modulation contrast exceeds 50% with a peak modulation contrast of 87% at 1.38 THz. The pixels of the SLM consist of mirror arrays that can be selectively actuated by a bias voltage of 35 V. Each individual pixel can either work as a grating, that diffracts terahertz radiation away from the detector, or as a flat mirror, that reflects all terahertz radiation into the detector. The mirrors have a size of 220 μm x 100 μm. Due to the wide frequency working bandwidth of more than 1 THz, such modulators can be used as spatial light modulators in terahertz coded aperture imaging spectroscopes with single-pixel detectors.

Fibonacci or bifocal terahertz (THz) imaging based on silicon diffractive zone plate in a continuous wave mode at 0.6 THz is demonstrated. Silicon as a low absorbing material was used in the laser ablation process to fabricate the Fibonacci structures. Zone plates were designed by the three-dimensional finite-difference time-domain method. To illustrate the Fibonacci focusing, the performance was studied both theoretically and experimentally by determining spatial profiles, the distance between the foci and the focal depth at frequencies of 0.3 THz and 0.6 THz. Terahertz images of various packaged objects at the 0.6 THz frequency were simultaneously recorded with the spatial resolution of wavelength in two different planes separated by 7 mm distance. Imaging performance using the Fibonacci lens is compared with the operation of the conventional silicon phase zone plate.

Light absorption in graphene causes a significant change in electron temperature due to the low electronic heat capacity and weak electron-phonon coupling. This property makes graphene a beautiful material for hot-electron bolometers (HEB). However, along with the above advantages, a major challenge remains that, with weak electron-phonon scattering, the resistance is only weakly temperature dependent for pristine graphene. It is thus challenging to measure the electron temperature change due to incoming radiation power. In addition, thermally isolating graphene in order to achieve the small electron-phonon thermal conductance is difficult. To overcome this issue, stronger temperature dependence has been obtained either by using dual-gated bilayer graphene to create a tunable bandgap or by introducing defects to induce strong localization. Both schemes have successfully produced bolometric detection, with responsivities up to 2×105 V W−1 and a temperature coefficient for the resistance as high as 22 kΩ K−1 at 1.5 K. Here we use graphene quantum dots, where a bandgap is induced via quantum confinement and the graphene quantum dots device exhibits an extraordinarily high variation of resistance with temperature (higher than 430 MΩ K−1), leading to responsivities of 1 × 1010 V W−1.

Utilization of sources generating short optical pulses requires techniques for the monitoring of the temporal characteristics of the pulses. The monitoring is often performed by an interferometric autocorrelation technique with detectors which possess higher-order nonlinearity. In the optical and mid-infrared spectral domains, one often employs quadratic detection exploiting two-photon absorption or sum-frequency generation. In the THz frequency domain, finding convenient detectors for the monitoring of pulsed sources remains to be a challenge. One option is quantum-engineered devices, exploiting, for example, intersubband transitions, but due to the low THz photon energy, such detectors require cryogenic cooling. Recently, we proposed to exploit electrical rectification in antenna-coupled field-effect transistors (FETs) which provide electrically controllable higher-order nonlinearities and temporal resolution on a picosecond scale [1,2]. Such detectors can be operated at room temperature and be used with different pulsed THz radiation sources. Here we will present physical explanation for this phenomenon and will demonstrate its application in nonlinear THz autocorrelation experiments. [1] A. Lisauskas et al., “Field-effect transistors as electrically controllable nonlinear rectifiers for the characterization of terahertz pulses,” APL Photonics, vol. 3, no. 5, p. 051705, May 2018. [2] K. Ikamas, I. Nevinskas, A. Krotkus, and A. Lisauskas, “Silicon Field Effect Transistor as the Nonlinear Detector for Terahertz Autocorellators,” Sensors, vol. 18, no. 11, p. 3735, Nov. 2018.

Performance of terahertz (THz) photoconductive devices, including detectors and emitters, has been improved recently by means of plasmonic nanoantennae and gratings. However, plasmonic nanostructures introduce Ohmic losses, which limit gains in device performance. In this presentation, we discuss an alternative approach, which eliminates the problem of Ohmic losses. We use all-dielectric photoconductive metasurfaces as the active region in THz switches to improve their efficiency. In particular, we discuss two approaches to realize perfect optical absorption in a thin photoconductive layer without introducing metallic elements. In addition to providing perfect optical absorption, the photoconductive channel based on all-dielectric metasurface allows us to engineer desired electrical properties, specifically, fast and efficient conductivity switching with very high contrast. This approach thus promises a new generation of sensitive and efficient THz photoconductive detectors. Here we demonstrate and discuss performance of two practical THz photoconductive detectors with integrated all-dielectric metasurfaces.

Coherent imaging is a well-established technique in the THz range, in this paper we explore the coherent continuous-wave (CW) THz imaging by recording the complex-valued spatial Fourier spectrum in the focal plane of the imaging system, and by utilizing the Fast Fourier Transform (FFT) technique to numerically retrieve both the intensity and the phase information of the object. System is built up based on the heterodyne detection consisting of two electric multiplier chain locked to each other with a slightly frequency off-set and a narrow-band CMOS TeraFET detector, aiming at the recording and reconstruction of 2D and 3D scenes. With a detection area of 80×70mm² and a sampling rate of 1pixel/mm² , both 7.6-cm-diameter 2D intensity image and 3D tomography extracted from the phase information of the object are reconstructed, which also reveals the system a capability of covering a large field of view (FOV).

We report that the intensity of the terahertz pulse is significantly enhanced by placing the femtosecond laser induced air plasma into a high-voltage DC electric field, which is generated by two parallel metal electrode plates. We experimentally demonstrate that the intensity of the terahertz pulse enhances linearly with the increase of the external electric field magnitude. We also find that the width of the effective spectrum decreases as the bias voltage increases, and the center frequency shifts to the low frequency. Furthermore, we find an optimal solution for applying the external electric field by changing the angle of the two parallel metal electrode plates. We speculate that the above phenomenon is mainly due to the plasma current generating terahertz and the bias electric field can drive the current in the plasma to enhance the terahertz signal.

Terahertz digital holography is an attractive combination of terahertz imaging and digital holography, which possesses the unique propagation and penetration ability of terahertz radiation as well as the advantages of high spatial resolution full-field phase-contrast imaging. We proposed a continuous-wave off-axis reflective terahertz digital holography to measure the morphology of the object. An experimental setup was built using a 2.52 THz (118.83 μm) far-infrared gas laser 295-FIR and a pyroelectric array detector. The field of view was expanded by stitching the reconstructed amplitude and phase distributions of three consecutive holograms after sub-pixel registration.

Measuring in real-time two phase flow composition of a mixed fluid having high gas void fraction (GVF) remains a challenging task in oil-gas fields. Such fluid is abundant in gas pipelines where pressure and temperature fluctuations lead to condensate gas. This may also be the case of crude oil produced from CO2 or steambased enhanced oil recovery (EOR); where the injected gas is mixed with the produced oil. This paper presents a new concept of high GVF measurement using a Terahertz-based imaging system. It explores the fact the gas phase has very low absorption of THz waves, while it yields an absorption factor that is proportional to the amount of liquid. The recent availability of low cost THz imaging systems that can generate two dimensional (2D) images at more than 100 frames/seconds make them well suitable for flow metering applications. Two different Artificial Intelligence (AI) algorithms, namely Support Vector Machine (SVM) and Artificial Neural Network (ANN), were assessed using an inhouse multiphase flow loop. The corresponding results reveal that while ANN and SVM yield very accurate results, the SVM technique performed slightly better where a maximal error of 0.46 % for GVF in the GVF range from 80 to 100% could be achieved. This suggests that the technique can be considered as a good candidate for next generation flow metering and imaging of multiphase flows.