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The main reason for the alternation of terahertz (THz) response in biological samples is the transition of a part of water from its free to bound state and back. To analyze such results, a precise spectrum of bound water within THz range should be known. The suggested wet powder spectroscopy method is optimal for this task. We measured the THz transmission of dry glucose pressed into pellets. Then, we added a small amount of water to these pellets and again measured the THz spectra. The contribution from the free water state starts to appear in resulting THz spectra after water concentration in glucose samples reaches 14–16%. Just below is the optimal point to extract the spectral contribution from bound water. We extracted the absorption and refraction spectra of bound water and confirmed that they are an order of magnitude weaker than those of free water within 0.07–1-THz range.

In this paper, we measure broadband terahertz spectra from a single 744-nm filament produced in tight, medium, and loose geometrical focusing conditions. Terahertz spectra are measured using interferometer coupled to a helium-cooled bolometer avoiding any cutoff frequencies. Based on THz spectrum maximum position and spectral width, we estimate electron-heavy particle (neutrals and ions) collision rate. Numerical simulations are performed using the state-of-the-art model of unidirectional femtosecond pulse propagation and convergence/divergence of optical radiation at large angles.

Sensitivity of the THz frequency range to the solutions of biomolecules originates from the decrease of absorption and dispersion of water in its bound state. Correct measurement and interpretation of the THz spectra of water-containing samples is still a challenging task because the reliable relaxation model for such spectra is not well established. The transmission and the attenuated total internal reflection geometries data were combined for precise analysis of the spectra of the aqueous solutions of bovine serum albumin within the range 0.05–3.2 THz. We compare the concentration dependencies of the dielectric function at “low,” “middle,” and “high” frequency and do not confirm an anomalous increase in absorption for concentrations below 17 mg/mL published by other teams.

This study explores a new type of terahertz-radiation source based on a molecular crystal of rubidium acid phthalate (RbAP) and a tunable metamaterial that functions as a filter. The high-quality oscillatory response of the RbAP crystal lattice in the terahertz frequency range enables the generation of narrowband terahertz radiation at multiple frequencies simultaneously, with high spectral brightness and peak power. Single femtosecond laser pulses excite the crystal. Switching between the generated spectral lines is achieved using a planar metamaterial, the absorption lines of which depend on the incident radiation polarization. The developed source allows for dynamic tuning of the emission spectral line, which makes it more versatile and efficient than conventional narrowband sources, such as quantum cascade lasers.

We report on the results of experimental studies of the photocurrent (PC) of photodiodes based on GaAs p-i-n structures with InAs/GaAs(001) double asymmetric quantum dot (DAQD) arrays obtained by self-assembling in the process of low-pressure metal-organic vapor phase epitaxy (LP-MOVPE). Three peaks were observed in the dependence of the PC on the reverse bias, measured under photoexcitation with a photon energy equal to the energy of the interband ground state transition in larger InAs QDs. These peaks were attributed to photoexcitation of electrons from the ground hole states in larger QDs into the ground electron states followed by resonant dissipative (with absorption or emission of optical phonons) and conservative tunneling into the GaAs conduction band via the ground electron states in smaller QDs. The PC dependence on the bias voltage agrees qualitatively with the theoretical field dependence of the probability of 1D dissipative tunneling between the QDs.

Intense electromagnetic fields can be obtained now in THz frequency range. THz pulses with electric field intensity above 1 MV/cm are now requested for strong-field applications like particle acceleration, short electron bunches measurements, controlling the state of the matter. The advantage of a THz pulse in comparison with the visible frequency range is the almost non-oscillating field that interacts with charged particles more efficiently. The advantage over a direct field is the ability to remotely focus this radiation in space and in time. Except for the huge free-electron lasers facilities, the only way to get THz pulses of MV/cm intensity is the conversion of high-power femtosecond laser pulses. We compare two ways of generating intense THz pulses using the radiation of TW and GW laser systems operating at 800 nm. They are two-color filamentation in gas and optical rectification in nonlinear crystals. The prospects for scaling of THz generation methods for a petawatt laser are discussed.

Aqueous solutions of guanylurea hydrogen phosphite (GUHP) have been synthesized. The temperature dependence of equilibrium GUHP concentration in water was obtained. The change in the density of aqueous GUHP solutions with a change in their concentration was investigated. The influence of the solution pH on the GUHP solubility in water in the temperature range of +25–45°C was analyzed. The crystallization range of monoclinic GUHP crystals, belonging to the sp. gr. Cc , was determined. GUHP crystals were grown using different methods, based on cooling or maintaining a constant temperature, with mixing aqueous solutions or without mixing. The properties of the grown crystals in the optical and THz ranges were investigated.