Vladimir N. Kurlov

Sapphire fibres grown by a modified internal crystallisation method

Abstract Single-crystal c -axis Al 2 O 3 fibres were grown by the modified internal crystallisation method, and were evaluated as reinforcements for high-temperature composites. Fibres were characterised by orientation, shape and mechanical properties. Growth procedures and fibre properties are reported.

Experimental and theoretical study of the diffraction properties of various crystals for the realization of a soft gamma-ray Laue lens

Crystals are the elementary constituents of Laue lenses, an emerging technology which could allow the realization of a space borne telescope 10 to 100 times more sensitive than existing ones in the 100 keV - 1.5 MeV energy range. This study addresses the current endeavor to the development of efficient crystals for the realization of a Laue lens. In the theoretical part 35 candidate-crystals both pure and two-components are considered. Their peak reflectivity at 100 keV, 500 keV and 1 MeV is calculated assuming they are mosaic crystals. It results that a careful selection of crystals can allow a reflectivity above 30% over the whole energy range, and even reaching 40% in its lower part. Experimentally, we concentrated on three different materials (Si_{1-x}Ge_x with gradient of composition, mosaic Cu and Au) that have been measured both at ESRF and ILL using highly-monochromatic beams ranging from 300 keV up to 816 keV. The aim was to check their homogeneity, quality and angular spread (mosaicity). These crystals have shown outstanding performance such as reflectivity up to 31% at ~600 keV (Au) or 60% at 300 keV (SiGe) and angular spread as low as 15 arcsec for Cu, fulfilling very well the requirements for a Laue lens application. Unexpectedly, we also noticed important discrepancies with Darwins model when a crystal is measured using various energies.

Growth of shaped sapphire crystals using automated weight control

Abstract The automated control systems have been developed for the growth of various sapphire crystals by edge-defined film-fed growth (EFG) and noncapillary shaping (NCS) methods. Automated crystal weight control is based on the analysis of the behaviour of the mass rate deviation at all stages of the growth process (seeding, crystal expansion, stationary growth, in-situ cross-sectional changing). The maintenance of the mass rate deviation in a certain range provides the crystal quality control as well as crystal shape control.

Nanoscintillators for Microscopic Diagnostics of Biological and Medical Objects and Medical Therapy

The main focus of this paper is the description of qualitatively new facilities for diagnostics of biological and medical objects and medical therapy obtained by applications of nanocrystalline scintillators. These facilities are based on abilities of nanoscintillators to selective conjugation with various biomolecular objects and noticeable variations of their atomic structures, X-ray diffraction (XRD) patterns, and light-emission characteristics induced by modifications of conditions on their external surfaces. Experimental results presented in this paper provide development of detection in vivo just inside a living organism of various viruses, cancer cells, and other pathological macromolecules by means of scanning X-ray diffractometry of nanoparticles introduced into the body. These data are produced by selective adsorption of pathological bioobjects by these nanoparticles and subsequent modifications of their XRD patterns. Application of narrow collimated X-ray beams and new types of X-ray detector matrices providing microscopic spatial resolution due to usage of nanoscintillators enables determination of the regions where these pathologies are localized with high accuracy. The procedure of detection of pathological organelles by this method improves possibilities for effective destruction of these pathologies by low-dose X-ray irradiation of the places of their localization. High effectiveness of this X-ray destruction is provided by concentrated absorption of X-ray quanta by the nanoscintillators and direct transfer of the absorbed energy to the pathological objects that are attached to the absorbing particles. Constructions of 3-D radiation detector matrices providing necessary microscopic spatial and angular resolutions of X-ray imaging are described on the basis of nanoscintillators, fiber light guides, and microcapillary matrices.

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.

Fabrication, properties and usage of single-crystalline YAG fibres

Abstract Single crystalline YAG fibres are now produced by an internal crystallization method. Essentially, the method is crystallization of the oxide melt infiltrated into continuous channels made in an auxiliary matrix, normally molybdenum, and then extracting the fibre from the auxiliary matrix by chemical dissolution of it. The method is relatively simple and requires sufficiently small energy input into a real process of the fibre production. Because crystallising a batch of the fibres by using ICM is actually similar to making bulk crystals an expected cost of ICM fibres is of the same order of magnitudes as that of bull crystals. It is shown that usage of ICM–YAG-fibres in a Ni-based matrix yields composites with high fibre/matrix interface strength and, hence, high creep resistance at very high temperatures for Ni-based materials.

Fabrication of near-net-shaped sapphire domes by noncapillary shaping method

Near-net-shaped sapphire domes were successfully grown directly from the melt by novel noncapillary shaping method (NCS method). NCS combines EFG capillary feeding and bulk growth sequentially. The obtained blanks up to 80 mm diameter demonstrated a high crystalline and optical quality. Several near-net-shaped sapphire domes were grown in the course of one growth process.

Solid immersion terahertz imaging with sub-wavelength resolution

We have developed a method of solid immersion THz imaging—a non-contact technique employing the THz beam focused into evanescent-field volume and allowing strong reduction in the dimensions of THz caustic. We have combined numerical simulations and experimental studies to demonstrate a sub-wavelength 0.35λ0-resolution of the solid immersion THz imaging system compared to 0.85λ0-resolution of a standard imaging system, employing only an aspherical singlet. We have discussed the prospective of using the developed technique in various branches of THz science and technology, namely, for THz measurements of solid-state materials featuring sub-wavelength variations of physical properties, for highly accurate mapping of healthy and pathological tissues in THz medical diagnosis, for detection of sub-wavelength defects in THz non-destructive sensing, and for enhancement of THz nonlinear effects.

The noncapillary shaping (NCS) method: a new method of crystal growth

Abstract A new method for growing shaped crystals was developed, called the “noncapillary shaping” (NCS) method. Crystals of sapphire and other oxide compounds with constant and variable cross-sections without gas inclusions in their volume were grown by the NCS method.

Tunable two-dimensional assembly of colloidal particles in rotating electric fields

Tunable interparticle interactions in colloidal suspensions are of great interest because of their fundamental and practical significance. In this paper we present a new experimental setup for self-assembly of colloidal particles in two-dimensional systems, where the interactions are controlled by external rotating electric fields. The maximal magnitude of the field in a suspension is 25 V/mm, the field homogeneity is better than 1% over the horizontal distance of 250 μm, and the rotation frequency is in the range of 40 Hz to 30 kHz. Based on numerical electrostatic calculations for the developed setup with eight planar electrodes, we found optimal experimental conditions and performed demonstration experiments with a suspension of 2.12 μm silica particles in water. Thanks to its technological flexibility, the setup is well suited for particle-resolved studies of fundamental generic phenomena occurring in classical liquids and solids, and therefore it should be of interest for a broad community of soft matter, photonics, and material science.