A. Andriesh’s research while affiliated with Academy of Sciences of Moldova and other places

A high sensitivity speckle based fiber-optic method for registration of low intensity IR radiation is described. The method is based on the effect of variation of the speckle pattern in the far-field of a multimode fiber. IR radiation that falls on a lateral surface of the fiber leads to variation of the speckle image. Computer processing of the speckle image provides information on the amplitude of perturbation that interacts with the fiber. An algorithm was developed for processing of the speckle image and determining of the intensity of IR radiation. The results of the computer simulation correlate well with the experimental ones.

In this paper we report about a possibility of application of chalcogenide glasses as active media in optoelectronic temperature sensors. All investigations were performed on a sample of Ge18As18Se64 chalcogenide glass as typical covalent network glass with rigid structure. Temperature dependence of optical transmission in the fundamental optical absorption edge region was studied through the glass transition interval. A monotone increasing temperature dependence of position of the fundamental optical absorption edge at the half maximum of its intensity was observed through the whole investigated temperature range as well as quasi-linear dependence upon the temperature in the region below glass transition.

A high sensitivity fiber-optic method for registration of low intensity IR radiation is proposed. The method is based on the effect of variation of the speckle pattern in the far-field of a multimode fiber. IR radiation that falls on a lateral surface of the fiber leads to variation of the speckle image. Computer processing of the speckle image provides information on the amplitude of the perturbation that hits the fiber. An algorithm has been developed for processing of the speckle image and determining of the intensity of IR radiation. The results of computer simulation correlate sufficiently well with experimental ones.

The paper presents a brief review of optical properties of infrared optical fibers based on chalcogenide glass materials. The most representative results on optical transmission of chalcogenide glasses used for fabrication of IR fibers as well as photo-induced absorption features in chalcogenide glass fibers are presented.

Diffraction optical structures are the main elements of diffraction optics with the perspectives for application in the systems of filtering, multiplexing, routing, focusing, and collimating of the light, as well as for fabrication of the photonic crystals. Thin films prepared from chalcogenide glasses and polymers were used for the fabrication of diffractive structures by holographic and electron-beam recording technology. The electric field and other technological procedures have been used during the holographic writing process in order to increase the diffraction efficiency and the spatial density of the recording media. The problem of obtaining low-cost but efficient luminescent materials is still present. It was shown that intensive luminescence is manifested from composite materials consisting of arsenic sulfide and arsenic selenide doped with rare-earth ions (Dy3+ and Pr3+), and polymers polyvinylalcohol or polyvinylpyrrolidone.

Thin luminofore layers of nanocomposites (NC) on a base of copolymer styrene and butylmethacrilate (SBMA) and of organic luminofores 5-(4-dimethylamino-benzylidene)-pyrimidine-2,4,6-trione (PI) or 3-(4-dimethylamino-phenyl)-1-(4-isothiocyanato-phenyl)-propenone (PII) are obtained. The dimensions of PI and PII particles are less than 100 nm and they are uniformly distributed in a matrix of polymer. The absorption of NC reveals bands of absorption with maxima at 470, 432 and 340 nm for PI-SBMA and 443 nm for PII-SBMA. The photoluminescence (PL) of NC reveals an intensive wide band at 532 nm for PI-SBMA and 5 bands at 450, 490, 518, 640 and 700 nm for PII-SBMA.

Vibrational and structural properties of GexSb40 xS60 (x = 25, 27, 35) chalcogeide glasses are studied in unmodified and gamma-radiation-modified states by using infrared spectroscopy, high-energy synchrotron x-ray diffraction and extended x-ray absorption fine structure spectroscopy. An agreement between radiation-induced structural changes and vibrational properties measured is established. It is suggested that the atomic pairs with wrong coordination created in the framework of coordination topological defect formation concept play a key role in the formation of radiation-modified state of the investigated glasses. Advantages and disadvantages of post-technological radiation-modification of chalcogenide glasses are considered within configuration coordinate model for description of unmodified and radiationmodified states.

Thin films prepared from chalcogenide glasses and polymers were used in the fabrication of diffractive structures by holographic and electron recording technology.

Thin layers of composite and nanocomposite material based on the amorphous arsenic sulfide and polymer polyvinylpyrrolidone (PVP), received by chemical dissolution As2S3 and composite separately, mixing and deposition on various substrates (silica glass, polyethylene terephthalate and monocrystalline silicon, etc.) have been investigated. Research of morphology of layers has revealed, that composites represent a polymeric material as matrix in which As2S3 spheroids with sizes of 1 µm and less distributed in regular intervals and depend on conditions of technology of obtaining. Optical transmission, refractive index and the diffraction efficiency of holographic record on thin layers of composites were measured. Composite retains many properties of the initial components from which they are prepared. The decreasing of the As2S3 component in the composite leads to absorption edge shift to higher energies and spheroid dimensions decreasing. Optical properties of the composites are changed due to ultraviolet (UV) light irradiation. This allows to utilize these structures for optical recording of information in particular holographic recording of diffraction gratings. The investigated new composites are perspective for different photonic devices as well as for recording media with high resolution.