Irina A. Shikunova

Terahertz Photonic Crystal Waveguides Based on Sapphire Shaped Crystals

In this paper, an ability for highly efficient terahertz (THz) waveguiding in multichannel sapphire shaped crystals is demonstrated. The edge-defined film-fed growth (EFG) technique (or Stepanov technique) of shaped crystal growth has been implemented to manufacture the THz photonic crystalline (PC) waveguide. The PC waveguide has been characterized using both numerical simulations and experimental study. It allows guiding the THz waves in multimode regime with the minimal dispersion in frequency range of 1.0-1.55 THz and the minimal power extinction coefficient of 0.02 dB/cm at 1.45 THz. The mode interference phenomenon has been observed in this waveguide highlighting the prospectives of its use for intrawaveguide interferometry. These results demonstrate the capabilities of combining the EFG/Stepanov technique advantages with unique properties of sapphire, such as relatively low THz-wave absorption, high mechanical, thermal, chemical, and radiation strength, for manufacturing the THz waveguides characterized with low loss and dispersion and suitable for use in wide range of THz technology applications in biomedical and material sciences, including sensing in aggressive environment.

Growth of Sapphire Ribbons with Capillary Channels for Laser Spectroscopy

Sapphire ribbons with extended capillary channels 450–600 μm in diameter were grown from melt by the Stepanov technique in order to develop a new scalpel capable of fluorescent diagnostics of the state of biological tissue. An automated system was built which allows one to control the shape and quality of sapphire ribbons at all growth stages.

Numerical simulation of terahertz-wave propagation in photonic crystal waveguide based on sapphire shaped crystal

Terahertz (THz) waveguiding in sapphire shaped single crystal has been studied using the numerical simulations. The numerical finite-difference analysis has been implemented to characterize the dispersion and loss in the photonic crystalline waveguide containing hollow cylindrical channels, which form the hexagonal lattice. Observed results demonstrate the ability to guide the THz-waves in multi-mode regime in wide frequency range with the minimal power extinction coefficient of 0.02 dB/cm at 1.45 THz. This shows the prospectives of the shaped crystals for highly-efficient THz waveguiding.

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.

A concept of cryoapplicator based on sapphire shaped crystal enabling control of the ice ball formation using spatially-resolved elastic backscattering of light

We have proposed a concept of monitoring ice ball formation in biological tissues during cryodestruction process via spatially-resolved detection of elastic light backscattering. For this purpose, we developed an experimental setup for study cryodestruction by using applicators based on sapphire shaped crystals with internal channels for optical irradiation of biotissues and detection of backscattered light. Due to the unique physical properties of sapphire, i.e. high thermal, mechanical, and chemical strength, high thermal conductivity and optical transparency, the sapphire cryoapplicators yield combination of the tissue cryodestruction with the optical control of tissue freezing. We have shown experimentally that using the proposed concept of applicator with several channels, it is possible to monitor changes of the ice ball during the cryodestruction process.

Technological aspects of manufacturing terahertz photonic crystal waveguides based on sapphire shaped crystals

Recently, terahertz (THz) photonic crystal waveguides based on sapphire shaped crystals have been proposed. These waveguides combine unique properties of sapphire with advantages of the edge-defined film-fed growth (EFG) or Stepanov technique of shaped crystal growth and allow guiding THz waves in a wide spectral range with small dispersion and losses. The sapphire photonic crystal waveguides are capable for operation in aggressive environment, which makes possible to perform high-temperature and high-pressure THz measurements, as well as THz measurements of aggressive chemicals. In this paper, the technological aspects of sapphire THz photonic crystal waveguide manufacturing by the EFG/Stepanov technique (including, the problems of seeding and automated control of multichannel shaped crystal growth) have been described. Prospective applications of sapphire photonic crystal waveguides in various branches of THz science and technology have been discussed.

Multi-spectral endogenous fluorescence imaging for bacterial differentiation

In this paper, the multi-spectral endogenous fluorescence imaging was implemented for bacterial differentiation. The fluorescence imaging was performed using a digital camera equipped with a set of visual bandpass filters. Narrowband 365 nm ultraviolet radiation passed through a beam homogenizer was used to excite the sample fluorescence. In order to increase a signal-to-noise ratio and suppress a non-fluorescence background in images, the intensity of the UV excitation was modulated using a mechanical chopper. The principal components were introduced for differentiating the samples of bacteria based on the multi-spectral endogenous fluorescence images.

Neurosurgical sapphire handheld probe for intraoperative optical diagnostics, laser coagulation and aspiration of malignant brain tissue

In this paper, a handheld contact probe based on sapphire shaped crystal was developed for the intraoperative optical diagnosis and aspiration of malignant brain tissue combined with the laser hemostasis. Such a favorable combination of several functions in a single instrument significantly increases its clinical relevance. It makes possible highly-accurate real-time detection and removal of either large-scale malignancies or even separate invasive cancer cells. The proposed neuroprobe was integrated into the clinical neurosurgical workflow for the intraoperative fluorescence identification and removal of malignant tissues of the brain.

Principle component analysis and linear discriminant analysis of multi-spectral autofluorescence imaging data for differentiating basal cell carcinoma and healthy skin

In present paper, an ability to differentiate basal cell carcinoma (BCC) and healthy skin by combining multi-spectral autofluorescence imaging, principle component analysis (PCA), and linear discriminant analysis (LDA) has been demonstrated. For this purpose, the experimental setup, which includes excitation and detection branches, has been assembled. The excitation branch utilizes a mercury arc lamp equipped with a 365-nm narrow-linewidth excitation filter, a beam homogenizer, and a mechanical chopper. The detection branch employs a set of bandpass filters with the central wavelength of spectral transparency of λ = 400, 450, 500, and 550 nm, and a digital camera. The setup has been used to study three samples of freshly excised BCC. PCA and LDA have been implemented to analyze the data of multi-spectral fluorescence imaging. Observed results of this pilot study highlight the advantages of proposed imaging technique for skin cancer diagnosis.