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In this contribution, we discuss the features of design and polarimetric inspection of terahertz achromatic waveplates. The design of the crystalline quartz half-wave plate was performed taking into account the ellipticity and the introduced phase difference between the orthogonal components of the output radiation polarization vector. The designed waveplate are relatively thin, work equally efficiently in the frequency range from 0.4 to 1.4 THz, and, most importantly, are cheap to manufacture. The modification of the experimental terahertz time-domain spectroscopy polarimetric setup involving direct waveform detection is proposed. The proposed polarimetry THz time-domain spectrometer with electro-optic detection shows parasitical signals absence and easier measurement procedure.

Speckle patterns can be very promising for many applications due to their unique properties. This paper presents the possibility of numerically and experimentally formation of speckle patterns using broadband THz radiation. Strong dependence of the statistical parameters of speckles, such as size and sharpness on the parameters of the diffuser are demonstrated: the correlation length and the mean square deviation of the phase surface inhomogeneity. As the surface correlation length is increasing, the speckle size also increases and its sharpness goes down. Alternatively, the magnification of the standard deviation of the surface height leads to the speckle size diminishing and growth of the speckle sharpness. The dimensions of the experimentally formed speckles correspond to the results of numerical simulation. The possibility of utilizing formed speckle patterns for the implementation of the ghost imaging technique has been demonstrated by methods of numerical modeling.

Time-resolved terahertz spectroscopy has become a common method both for fundamental and applied studies focused on improving the quality of human life. However, the issue of finding materials applicable in these systems is still relevant. One of the appropriate solution is 2D materials. Here, we demonstrate the transmission properties of unique graphene-based structures with iron trichloride FeCl3 dopant on glass, sapphire and Kapton polyimide film substrates that previously were not investigated in the framework of the above-described problems in near infrared and THz ranges. We also show properties of a thin tungsten disulfide WS2 film fabricated from liquid crystal solutions transferred to a polyimide and polyethylene terephthalate substrates. The introduction of impurities, the selection of structural dimensions and the use of an appropriate substrate for modified 2D layered materials allow to control the transmission of samples for both the terahertz and infrared ranges, which can be used for creation of effective modulators and components for THz spectroscopy systems. Electronic supplementary material The online version of this article (10.1186/s11671-019-3062-3) contains supplementary material, which is available to authorized users.

Terahertz (THz) time-domain holographic detection unit prototype for studying propagation dynamics of broadband vortex beams carrying optical angular momentum was developed. The setup consists of a femtosecond laser system, a THz radiation generator, a replaceable set of modulation components for shaping various OAM-beams, an optical delay line, and a wide-aperture electro-optical detecting module with 3D-printed mechanical parts. 3D-printed kinematic mounts of designed detection unit are available for public use as open-source hardware.

A method of ultrafast wireless information transmission using spectrum-sliced supercontinuum (SC) along the THz frequency range is presented in this letter. The THz spectrum-sliced SC was formed by femtosecond optical pulses doubled in a Michelson interferometer before being input onto a MgO:LiNbO3-THz generator. Two THz pulses generated by femtosecond pulses within a MgO:LiNbO3-crystal provided the spectrum-sliced SC in the spectral domain, which was recorded by an electro-optical detection system. The transmission rate in this method is determined by the bandwidth of the THz spectrum, the number of spectral lines in the SC, and the pulse repetition rate. We have demonstrated an SC containing 31 spectral lines with 23-GHz spacing within the range from 0.04 to 0.75 THz. The signal with encoded information was successfully transmitted over 2.4 m in free-space.

We proposed a simple and cost-effective method to manipulate the temporal and spectral properties of pulsed terahertz waves. A deep modulation of a pulse spectrum was both numerically and experimentally verified using Fresnel apertures with a radius ranging from several to several tens of the central wavelength of the broadband terahertz radiation. N-fold frequency minima were formed in the spectrum at a specific axial position behind the filter. Non-paraxial properties of this filter were also analyzed. A significant value (35%) of the ratio of the longitudinal to the transverse field component at the filter frequency was obtained. The measured results agree well with the simulation and theoretical predictions. The property of such a diffractive Fresnel notch filter can benefit the generation of longitudinal terahertz fields and relevant applications. publishedVersion

By doping ZnSe crystals with Fe2+ ions at a level of 0.23 wt. %, the transmission of broadband terahertz (THz) radiation from 0.4 to 0.5 THz range have been enhanced for up to 20%. The sample transmission was carried out using a terahertz time-domain spectroscopy setup. To explain the arising effect and changes in band structure, non-linear absorption of undoped and Fe-doped ZnSe samples were studying using femtosecond pump - supercontinuum probe spectroscopy in visible and NIR spectral ranges. Such enhanced transmission of Fe2+: ZnSe can be applied for creating terahertz radiation control devices.

This investigation presents a method of determining the frequency band of pulsed terahertz spectrometer for reliable research and technique for scan time decrease. Both methods lead to consistency and acceleration of data.

Paper presents tunable terahertz broadband phase-only modulator based on CdSe — CdS. It produces linear phase shift in broadband THz wave controlled by modulator illumination and bias voltage.

In this paper we study the influence of the period between U-shaped split-ring resonators (SRRs) on the trans- mission/absorbtion properties and refraction index of metasurfaces in THz frequency range (0.1 - 1 THz) using experiments and numerical simulations. The metasurfaces are formed by U-shaped SRRs arrays. The period varies from 63 to 300 μm The metasurface electromagnetic responses are obtained using terahertz time-domain spectroscopy. The experimental and numerical results reveal the shift in transmission spectra for the metasurface response and the tuning of absorbtion intensity at the period between U-shaped SRRs changing. The notable change in the metasurface refractive index is shown.

In the present paper research results of broadband THz radiation influence in a range 0.1÷2 THz on some biological tissues are presented. Theoretical modeling of THz radiation propagation through the fat sample is performed. Experimental absorption spectra of samples of vegetable oil, nail tissue, skin tissue and blood are obtained. Spectra of these tissues differ in a range of 0.1 ÷ 2 THz. Also they depend on water content. From these samples vegetable oil has the best transmission.