Irina N. Dolganova

Non-Destructive Evaluation of Polymer Composite Materials at the Manufacturing Stage Using Terahertz Pulsed Spectroscopy

Nowadays, composite materials are widely used in building and construction industry, in motor-vehicles, spacecrafts and aircrafts, and in biomedical science due to the ability of combining various consistent components for manufacturing composite materials with physical and chemical properties significantly different from the properties of each component. Polymer composite materials (PCMs) appear to be the most common type of composites. PCMs consist mainly of polymer binder reinforced with the glass-fiber-fabric. Although PCMs are widely applied, PCM manufacturing technology lacks the methods of non- destructive testing. In this paper we demonstrate that terahertz (THz) pulsed spectroscopy (TPS) appears to be a unique instrument for solving important problems of PCM manufacturing control. We experimentally demonstrate the efficiency of TPS for non-destructive control of PCM binder polymerization, since THz radiation is sensitive to changes of picosecond dynamics in media. Furthermore, we show the ability to detect the internal non-impregnated voids inside the PCM structure by means of THz time-of-flight tomography. These results highlight the potentials of TPS applications for non-destructive control of PCM manufacturing process.

A hybrid continuous-wave terahertz imaging system

A hybrid (active-passive mode) terahertz (THz) imaging system and an algorithm for imaging synthesis are proposed to enhance the THz image quality. The concept of image contrast is used to compare active and passive THz imaging. Combining the measurement of the self-emitted radiation of the object with the back-scattered source radiation measurement, it becomes possible to use the THz image to retrieve maximum information about the object. The experimental results confirm the advantages of hybrid THz imaging systems, which can be generalized for a wide range of applications in the material sciences, chemical physics, bio-systems, etc.

Scattering in structured two-layered medium

Multiple scattering in two-layered medium was modeled using Monte Carlo numerical simulation. Special case of group formation in such layers was considered. To estimate the impact of structure factor on the overall results, the rigorous calculation of single scattering phase function was used. Comparison with the Monte Carlo simulations for the respective model phase function shows that there were some differences in the scattered radiance. These differences had no significant energy redistribution in the angular dependence of the scattered radiance, but different elongation in the zero-direction occurred. So it was shown that the group formation and special structure still leaded to some changes in the scattering process, even if the medium had several layers with different parameters and had rather large width.

Peculiarity of Terahertz Waves Scattering

Scattering of terahertz (THz) radiation is considered to be a significant problem for many applications, since it has often multiple character and is followed by interference effects. We present the computational results of THz propagation through scattering layers, obtained by using Monte Carlo simulation scheme of radiation transfer. Dense package of particles is considered for enhancing the influence of structure factor. Interference effects are shown to play an essential role for scattering phase function and scattering angular distribution of THz radiance.

Monte Carlo simulation of optical coherence tomography signal of the skin nevus

Monte Carlo (MC) numerical simulation of light propagation in living tissue is widely used for characterization of optical coherence tomography (OCT) signals. Using MC simulation we obtained OCT images of skin with dysplastic nevus. Two various positions of skin nevus in depth were considered. Comparing these OCT simulation results with image of skin without nevus, we showed that OCT medical approach allows to detect dysplastic nevus at different stages of its life.

Terahertz solid immersion microscopy for sub-wavelength-resolution imaging of biological objects and tissues

We have developed a method of terahertz (THz) solid immersion microscopy for imaging of biological objects and tissues. It relies on the solid immersion lens (SIL) employing the THz beam focusing into the evanescent-field volume and allowing strong reduction in the dimensions of the THz beam caustic. By solving the problems of the sample handling at the focal plane and raster scanning of its surface with the focused THz beam, the THz SIL microscopy has been adapted for imaging of soft tissues. We have assembled an experimental setup based on a backward-wave oscillator, as a continuous-wave source operating at the wavelength of λ = 500 μm, and a Golay cell, as a detector of the THz wave intensity. By imaging of the razor blade, we have demonstrated advanced 0.2λ-resolution of the proposed THz SIL configuration. Using the experimental setup, we have performed THz imaging of a mint leaf revealing its sub-wavelength features. The observed results highlight a potential of the THz SIL microscopy in biomedical applications of THz science and technology.

Wavelet-domain de-noising of optical coherent tomography data for biomedical applications

Optical coherent tomography (OCT) is a rapidly developing method of fundamental and applied research. Detection and processing of OCT images is a very important problem of applied physics and optical signal processing. In the present paper we are demonstrating the ability for effective wavelet-domain de-noising of OCT images. We are realizing an algorithm for wavelet-domain de-noising of OCT data and implementing it for the purpose of studying test samples and for in vivo nail tomography. High de-noising efficiency with no significant losses of information about the internal sample structure is observed.

In vitro terahertz spectroscopy of gelatin-embedded human brain tumors: a pilot study

We have performed the in vitro terahertz (THz) spectroscopy of human brain tumors. In order to fix tissues for the THz measurements, we have applied the gelatin embedding. It allows for preserving tissues from hydration/dehydration and sustaining their THz response similar to that of the freshly-excised tissues for a long time after resection. We have assembled an experimental setup for the reflection-mode measurements of human brain tissues based on the THz pulsed spectrometer. We have used this setup to study in vitro the refractive index and the amplitude absorption coefficient of 2 samples of malignant glioma (grade IV), 1 sample of meningioma (grade I), and samples of intact tissues. We have observed significant differences between the THz responses of normal and pathological tissues of the brain. The results of this paper highlight the potential of the THz technology in the intraoperative neurodiagnosis of tumors relying on the endogenous labels of tumorous tissues.

Sapphire shaped crystals for laser-assisted cryodestruction of biological tissues

We have developed cryo-applicators based on the sapphire shaped crystals fabricated using the edge-defined film-fed growth (EFG) and noncapillary shaping (NCS) techniques. Due to the unique physical properties of sapphire: i.e. high thermal, mechanical, and chemical strength, impressive thermal conductivity and optical transparency, these cryo-applicators yield combination of the tissue cryo-destruction with its exposure to laser radiation for controlling the thermal regimes of cryosurgery, and with the optical diagnosis of tissue freezing. We have applied the proposed sapphire cryo-applicators for the destruction of tissues in vitro. The observed results highlight the prospectives of the sapphire cryo-applicators in cryosurgery.

Sapphire capillary interstitial irradiators for laser medicine

In this paper, we demonstrate instruments for laser radiation delivery based on sapphire capillary needles. Such sapphire irradiators (introducers) can be used for various medical applications, such as photodynamic therapy, laser hyperthermia, laser interstitial thermal therapy, and ablation of tumors of various organs. Unique properties of sapphire allow for effective redistribution of the heat, generated in biological tissues during their exposure to laser radiation. This leads to homogeneous distribution of the laser irradiation around the needle, and lower possibility of formation of the overheating focuses, as well as the following non-transparent thrombi.