We present the results of terahertz generation studies under excitation via femtosecond lasers pulses epitaxial films of InAs, which were synthesized on semi-insulating and highly doped GaAs substrates. It is shown that a terahertz emitter based on epitaxial InAs film grown on a heavily doped GaAs n-type substrate, has the same terahertz generation efficiency as the InAs-film emitter grown on a semi-isolating GaAs substrate, but it has a significantly better spectral resolution, which is mainly determined by the parameters of the optical delay line and the femtosecond laser’s stability.

We present the results of terahertz generation studies under excitation via femtosecond lasers pulses epitaxial films of InAs, which were synthesized on semi-insulating and highly doped GaAs substrates. It is shown that a terahertz emitter based on epitaxial InAs film grown on a heavily doped GaAs n-type substrate, has the same terahertz generation efficiency as the InAs-film emitter grown on a semi-isolating GaAs substrate, but it has a significantly better spectral resolution, which is mainly determined by the parameters of the optical delay line and the femtosecond laser’s stability.

Generation of a terahertz radiation in $\alpha$-Sn / Ge quantum wells by ultrashort laser pulses is studied. Existence of the $\alpha$-Sn at room temperature is shown by Raman spectroscopy. Cardinal differences were found in the parameters of THz pulses generated in samples with quantum wells widths of 4 nm, 6 nm sign and in nanostructures with quantum wells widths of 8.5 nm, 10 nm. The observed changes in the polarization dependences of the electric field of the THz radiation generated in $\alpha$-Sn/Ge nanostructures with changes in the width of quantum well going from 6 nm to 8.5 nm are associated with the transition from a normal band structure to an inverted one in these nanostructures.

An Erratum to this paper has been published: https://doi.org/10.1134/S1063785022140012

The possibility of obtaining spectra of the complex refractive index of mononucleotide films deposited on a polished silicon substrate in the terahertz (THz) range has been shown for the first time. The transmission of biopolymer samples with a THz spectrometer was measured. The natural absorption frequencies and refractive index spectrum of adenosine in the THz range were defined.

В настоящей работе представлены результаты экспериментального исследования фототоков в наноструктурах на основе квантовых ям α-Sn/Ge при их возбуждении фемтосекундными оптическими импульсами, как непосредственно контактным методом, так и регистрацией терагерцового излучения, индуцированного этими фототоками. Данная структура представляет интерес с точки зрения получения нового топологического материала. Исследуемые образцы представляли собой нанометровые слои Ge и α-Sn, синтезированные методом электронно-лучевого осаждения на поверхность подложки кремния с верхним слоем SiO2.

This work describes the possibility for reconstructing the optical properties of a biological object using terahertz pulse time-domain holography method (THz-PTDH). Flat pellets made from sublimated blood plasma (healthy and diabetic) were used as samples. As a result, we created a convenient model that based on experimentally measured THz fields provided by THz-TDS system. Using this model, it is possible to reconstruct spatial distributed optical properties, as well as frequency-dependent characteristics.

The experimental results of scattering and near-field interaction of a terahertz electromagnetic field with graphene ribbons near a metal probe of an atomic force microscope are reported. The amplification of a near-field terahertz scattering in ribbons is shown in comparison with unstructured graphene. The appearance of resonance peaks in the range 0.2–1.6 THz in the scattering spectra of terahertz radiation on graphene ribbons in the presence of a probe was detected, which is possibly due to the interaction of radiation with plasmons in the ribbons.

We observed a strong emission of terahertz radiation, in sandwich nanostructures made of Ge and α-Sn nanometer thick films. Together with the THz emission there arise photocurrent, induced by an irradiation of the structures with ultra-short optical pulses. There a strong generation of photon-drag currents of nonequilibrium Dirac (and/or Weil) electrons has been detected. This result and other discovered novel unique properties of the Ge/Sn multi-layers are indicating on an emergence of a new class of topological materials, where massless electrons have a strong interaction with the irradiated light.

We report on the experimental study of the scattering and the near-field interaction of a THz electromagnetic field with graphene layers near the probe of a terahertz near-field microscope. There are resonance lines in the spectrum for a graphene monolayer-based transistor structure, which is possibly due to the strong plasmon response at terahertz frequencies and the manifestation of plasmon interference in the graphene strip.

Experimental results obtained in a study of the effect of electron–hole plasma on the generation of terahertz (THz) radiation in semiconductor nanowires grown by metal-organic vapor-phase epitaxy (MOVPE) are presented. It is shown that the temporal dynamics of photoexcited charge carriers in semiconductor nanowires is determined by the transport of carriers, both electrons and holes, and by the time of capture of electrons and holes at surface levels.

This paper presents the experimental studies of the generation of terahertz radiation in periodic arrays of GaAs/AlGaAs core/shell nanowires via excitation by ultrashort optical pulses. It is demonstrated that terahertz emission occurs via excitation of photocurrent in the nanowires. The dynamics of photoinduced charge carriers is studied via the influence of an electron–hole plasma on terahertz radiation.

We report on the experimental study of the signal of near-field contribution to scattering of THz electromagnetic waves in ringlike microstructures using terahertz near-field microscope. It was established that terahertz near-field signal is strongly enhanced inside the ring.

Terahertz wave generation through optical rectification of femtosecond laser pulses and its detection in GaSe and GaSe1−xSx crystals with a relatively low (x = 0.04) and high (x = 0.29) content of sulfur was studied. The decrease of terahertz generation and detection efficiency at an increase of sulfur content in GaSe1−xSx was observed. The phase-matching conditions for electro-optical sampling in GaSe and GaSe1−xSx crystals were analyzed. The arising possibility to achieve the narrowing of terahertz detection bandwidth using thicker GaSe crystals was experimentally confirmed.

THz generation under excitation by ultrashort optical pulses from ordered arrays of GaAs nanowires is reported. It was found that the efficiency of THz generation is determined by the geometrical parameters of nanostructures and has a resonant character. Furthermore, it is shown that the terahertz generation efficiency at optimum geometrical parameters of an array of semiconductor nanowires is greater than the corresponding value for bulk semiconductor p-InAs which is the most effective THz emitter.

Представлены экспериментальные результаты исследования влияния электронно-дырочной плазмы на генерацию ТГц-излучения в полупроводниковых нитевидных нанокристаллах на основе GaAs, выращенных методами MOVPE. Было показано, что временная динамика фотовозбужденных носителей заряда в полупроводниковых нитевидных нанокристаллах определяется транспортом носителей заряда, как электронов, так и дырок, временем захвата электронов и дырок на поверхностные уровни. DOI: 10.21883/FTP.2017.12.45177.40

The experimental results on the effect of an electron-hole plasma on the THz generation in GaAs NWs grown by MOVPE are presented. It is shown that the dynamics of photoexcited charge carriers in nanowires is determined by the transport of charge carriers - electrons and holes and by the capture time of electrons and holes onto the surface levels. The dependence of initial fall time of THz emission on the intensity of the pump can be accounted for by a theory based on majority-carrier flow. The characteristics time obtained can be used to determine the momentum relaxation time of the electrons.

The paper presents the results of experimental studies of the generation of terahertz radiation in periodic arrays of GaAs nanowires via excitation by ultrashort optical pulses. It is found that the generation of THz radiation exhibits resonant behavior due to the resonant excitation of cylindrical modes in the nanowires. At the optimal geometric parameters of the nanowire array, the generation efficiency is found to be higher than that for bulk p-InAs, which is one of the most effective coherent terahertz emitters.