M. M. Nazarov

Application of time-domain THz spectroscopy for studying blood plasma of rats with experimental diabetes

The absorption spectra of rat blood plasma have been studied by time-domain THz spectroscopy in the frequency range from 0.1 to 2.0 THz. The absorption coefficient of blood plasma is found to be significantly reduced, depending on the diabetes severity.

Analysis of blood plasma at terahertz frequencies

Terahertz time-domain spectroscopy in the 0.05-2.5 THz frequency range was employed to analyze blood plasma samples obtained from laboratory animals with experimental diabetes and from healthy controls. It was found that transmission and reflection coefficients of samples from rats with diabetes differed significantly from control values in both amplitude and phase. The cause of the detected differences is discussed with respect to variation in the terahertz response of water.

Determination of the refractive index of β-NaYF4/Yb3+/Er3+/Tm3+ nanocrystals using spectroscopic refractometry

A method for measuring refractive index n of nanosize particles in the visible and near-IR spectral ranges is proposed. The method is based on comparing refractive index ncolloid of a colloid solution of nanoparticles in several solvents with refractive indices nsolvent of corresponding pure solvents and has an accuracy of ±2 × 10−4. Upconversion nanosize phosphors (UCNPs) are synthesized in the form of a β-NaYF4 crystalline matrix doped with Yb3+, Er3+, and Tm3+ rare earth ions. UCNPs have a doped core with a diameter of 40 ± 5 nm and undoped shell with a thickness of 3–5 nm. Synthesized nanocrystals possess intense photoluminescence in the blue, green, and red spectral ranges upon excitation by IR radiation with a wavelength of 977 nm. Using a spectroscopic refractometer, the dispersion of the refractive index of β-NaYF4/Yb3+/Er3+/Tm3+ nanocrystals was measured for the first time in the spectral range of 450–1000 nm with an accuracy of ±2 × 10−4.

THz monitoring of the dehydration of biological tissues affected by hyperosmotic agents

Different ways for monitoring the dehydration of tissues affected by hyperosmotic agents have been comparatively analyzed to increase the THz transparency of biological tissues. The data obtained with an original THz laser spectrometer, a Nicolet 6700 Fourier spectrometer, and a Callegari Soft Plus system for skin diagnostics are in good agreement. The corresponding responses of biological tissues (in the form of THz transmittance, reflectance, absorption coefficient, and hydration coefficient) to the effect of biologically compatible hyperosmotic agents have been studied.

Study of the dielectric function of aqueous solutions of glucose and albumin by THz time-domain spectroscopy

We report a study of aqueous solutions of glucose and bovine serum albumin using THz time-domain spectroscopy. To describe the permittivity of the solutions of these substances, we use a simplified model being applicable in the frequency range of 0.05 – 2.7 THz. On the assumption that most of the water molecules become bound at high concentrations of glucose and protein in the solution, the changes in water characteristics are investigated. To improve the reliability of the results, the measurements are performed by two independent methods: the method of attenuated total internal reflection and the transmission method. Combination of the results obtained by these two methods allows expanding the spectral range towards lower frequencies.

Studying human and animal skin optical properties by terahertz time-domain spectroscopy

Human and rat skin reflection spectra and the effect of glucose and glycerol on these spectra are studied in vivo by terahertz time-domain spectroscopy in the frequency range of 0.1–2.0 THz. Variations in skin optical properties proved to correlate with changes in the blood glucose level.

Formation of channel optical waveguides in polymethylmethacrylate with embedded electro-optic chromophore DR13 by the photoinduced bleaching method

A composite polymeric material based on polymethylmethacrylate (PMMA) with embedded electro- optical (EO) chromophore DR13 is designed. Irradiation with electromagnetic radiation in the visible range leads to a bleaching of the composite and its refractive index n decreases due to the irreversible photodestruction of the chromophore. Changes in the absorption spectrum and refractive index of the composite with the irradiation time are measured. It is shown that the change in n depends on the concentration of DR13 in the polymer matrix and can reach a value of Δn = 0.034 in the telecommunication C-range near a wavelength of 1.55 μm. The rate of bleaching depends on the wavelength of the actinic light and reaches its maximum when the wavelength is near the maximum of chromophore absorption. With the use of the photobleaching method and the PMMA/DR13 composite, channel waveguides and the other elements of the integrated optical devices are fabricated, including waveguide splitters, directional couplers, and Mach–Zehnder interferometers. This simple one-step method does not involve the removal of polymer material by liquidphase or reactive ion etching.

Terahertz Response of a Polymer Composite with High Concentration of Silicon Micro- and Nanoparticles

The methods used for the formation of composite materials with a definite high refractive index in a terahertz (THz) frequency range due to the incorporation of silicon micro- or nanoparticles into a polymer-thermoplast matrix are considered. The dielectric properties of the composites are studied versus the concentration of silicon particles and THz radiation frequency. The maximum achievable limits of refraction, absorption, and scattering are determined. The possibility to use a composite material based on polyethilene impregnated with Si-nanoparticles for manufacturing THz optics elements is demonstrated.