22 pages, 12 figures, review paperInternational audienceResonant frequencies of the two-dimensional plasma in FETs increase with the reduction of the channel dimensions and can reach the THz range for sub-micron gate lengths. Nonlinear properties of the electron plasma in the transistor channel can be used for the detection and mixing of THz frequencies. At cryogenic temperatures resonant and gate voltage tunable detection related to plasma waves resonances, is observed. At room temperature, when plasma oscillations are overdamped, the FET can operate as an efficient broadband THz detector. We present the main theoretical and experimental results on THz detection by FETs in the context of their possible application for THz imaging

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The absolute spatial displacement of Bloch-oscillating electrons in semiconductor superlattices is measured as a function of time with a few angstrom resolution using a novel experimental technique: The oscillating Bloch wave packet creates a small dipole field which can be determined using the field shift of the Wannier-Stark ladder transitions as a sensitive detector. The total amplitudes and their dependence on the static electric field are in good agreement with a theory including excitonic effects.

The authors report on detection of terahertz radiation by high electron mobility nanometer InGaAs∕AlInAs transistors. The photovoltaic type of response was observed at the 1.8–3.1THz frequency range, which is far above the cutoff frequency of the transistors. The experiments were performed in the temperature range from 10to80K. The resonant response was observed and was found to be tunable by the gate voltage. The resonances were interpreted as plasma wave excitations in the gated two-dimensional electron gas. The minimum noise equivalent power was estimated, showing possible application of these transistors in sensing of terahertz radiation.

the manipulation of graphene and its derivatives occupy a relatively insignifi cant part, i.e., less than 1%. The fi rst publications on graphene modifi cation with laser irradiation appeared in 2008, however, since 2010, the number of publications has risen exponentially.Graphene oxide (GO) has emerged as a versatile material for nanocarbon research. Several types of oxygen-containing functional groups present on the basal plane, and the sheet edge allows GO to interact with a broad range of organic and inorganic materials. [ 9 ] Furthermore, GO is an abundant and low-cost material synthesized from graphite or graphite oxide; it retains a layered structure but, at the same time, it can be characterized by the loss of electronic conjugation caused by the oxy groups at the edge or plane defects. GO has a potential use in energy, [ 10 ] electronics, [ 11 ] molecular sensing areas, [ 12 ] catalysis, [ 13 ] etc. Moreover, it can be reduced chemically or thermally in order to achieve graphenelike properties. [ 14 ] The material produced during such a procedure is usually referred to as "reduced GO" (rGO). However, residual defects such as remnant oxygen atoms, [ 15 ] Stone-Wales defects (pentagon-heptagon pairs), [ 16 ] and holes [ 17 ] appearing due to the loss of carbon (in the form of CO or CO 2 ) from the basal plane [ 18 ] limit the electronic quality of rGO.A laser is a powerful tool which is used for various applications in industry, medicine, science, and material processing. [ 19 ] It is usually employed in different processes such as ablation, etching, cutting of various materials, as well as direct A dramatic rise in research interest in laser-induced graphene oxide (GO) reduction and modifi cation requires an overview of the most recent works on this subject. Typical methods for the recognition and confi rmation of modifi ed graphene and its derivatives, such as Raman, Fourier-transform infra-red (FTIR), X-ray photoelectron (XP), and ultraviolet-visible (UV-vis) spectroscopies, are introduced briefl y in this review. A major part of the survey is devoted to the main modifi cation ways and the laser parameters used in the literature. A discussion of possible reduction and modifi cation mechanisms is also presented. Recent applications, especially in the biomedical fi eld such as cell therapy treatment, as well as signifi cant results of GO modifi cation, are discussed in detail. Finally, perspectives for the application of laser-induced GO modifi cations in passive THz photonics and biomedicine are briefl y addressed.

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In this roadmap article, we have focused on the most recent advances in terahertz (THz) imaging with particular attention paid to the optimization and miniaturization of the THz imaging systems. Such systems entail enhanced functionality, reduced power consumption, and increased convenience, thus being geared toward the implementation of THz imaging systems in real operational conditions. The article will touch upon the advanced solid-state-based THz imaging systems, including room temperature THz sensors and arrays, as well as their on-chip integration with diffractive THz optical components. We will cover the current-state of compact room temperature THz emission sources, both optolectronic and electrically driven; particular emphasis is attributed to the beam-forming role in THz imaging, THz holography and spatial filtering, THz nano-imaging, and computational imaging. A number of advanced THz techniques, such as light-field THz imaging, homodyne spectroscopy, and phase sensitive spectrometry, THz modulated continuous wave imaging, room temperature THz frequency combs, and passive THz imaging, as well as the use of artificial intelligence in THz data processing and optics development, will be reviewed. This roadmap presents a structured snapshot of current advances in THz imaging as of 2021 and provides an opinion on contemporary scientific and technological challenges in this field, as well as extrapolations of possible further evolution in THz imaging.

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