Alexander I. Ignatiev

Chloride photo-thermo-refractive glasses

The known photo-thermo-refractive (PTR) glass is a photosensitive multi-component silicate glass containing fluorine and bromine and doped with cerium, antimony, and silver. The UV irradiation and subsequent heat treatment of this glass result in the crystalline phase precipitation and negative refractive index change up to 1000 ppm in the UV-irradiated area. This effect is used for holographic recording the volume Bragg’s gratings. In the present research, we developed and studied the new class of chlorine-containing PTR glasses in which the UV irradiation and subsequent heat treatment cause the precipitation of silver nanoparticles with a shell consisting of mixed silver and sodium chlorides. The growth of the shell on the silver nanoparticle was shown to lead to a local positive refractive index change in the UV-irradiated area against the unirradiated one up to 1500 ppm.

Photostructurable photo-thermo-refractive glass

Photostructurable properties of photo-thermo-refractive glass are discovered for the first time. The etching kinetics in HF solutions for virgin photo-thermo-refractive glass and glass ceramics are investigated. The etching rate of the glass ceramics is shown to be more than ten times higher than that of glass. Future prospects of applying the chemical etching technology for developing various PTR glass-based photonic and mechatronic elements are discussed.

Formation of luminescent centers in photo-thermo-refractive silicate glasses under the action of UV laser nanosecond pulses

It is shown experimentally that the result of the UV nanosecond laser irradiation of the silver-containing photo-thermo-refractive (PTR) glasses depends on the pre-history of glass. If the PTR glass was preliminary irradiated by the UV radiation by UV mercury lamp into the absorption band of Ce3+ ions the laser irradiation results in the silver molecular clusters (MCs) luminescence quenching. If the PTR glass was not preliminary irradiated by the UV radiation the UV nanosecond laser irradiation action results in the silver MCs luminescence appearance. The subsequent thermal treatment below the glass transition temperature results to the increase of the luminescence intensity. The thermal treatment above the glass transition temperature led to the silver nanoparticles formation and to luminescence quenching.

Optical Gradient Waveguides in Photo-Thermo-Refractive Glass Formed by Ion Exchange Method

Photo-thermo-refractive (PTR) glasses are the class of polyfunctional materials that combine the properties of several monofunctional materials such as photo-refractive, laser, luminescent, and plasmonic ones. Based on PTR glasses, various diffractive holographic elements and photonic devices were developed in both the volume and fiber versions. In this paper, the fabrication of optical planar waveguides on PTR glass by low-temperature ion exchange is reported for the first time. Planar waveguides were fabricated through substituting the sodium ions in glass by silver, potassium, rubidium, and cesium ones from the nitrate melts. The silver waveguides were shown to have the largest depth (27 μm) and reveal no birefringence. For the silver waveguides, an increase in the refractive index is caused by differences in the polarizabilities of cations exchanged. The maximum increment of the refractive index was observed in the cesium waveguides (0.0512). An increase in the refractive index and also appearing the birefringence in potassium, rubidium, and cesium waveguides are found to be due to the compressive mechanical stresses and their relaxation. The potentialities of the ion exchange technology for fabricating, in PTR glasses, planar gradient waveguides with low losses (0.5 dB/cm) are demonstrated, the potentialities extending the application field of PTR glasses in photonics.

Formation of luminescence centers and nonlinear optical effects in silver-containing glasses under femtosecond laser pulses

It is experimentally shown that irradiation of silver-containing silicate glass by IR femtosecond laser pulses leads to generation of free electrons in glass as a result of multiphoton ionization. Free electrons, being captured by charged molecular silver clusters, transform them into the neutral state, as a result of which the luminescence intensity along the laser-pulse track significantly increases. When a laser pulse propagates in glass, cubic nonlinearity dominates in the initial portion of the path, which leads to pulse self-focusing and filamentation. In the final portion of the path, the dominant process is self-defocusing, which is caused by the local decrease in the refractive index as a result of multiphoton generation of free electrons.

Luminescent glass fiber sensors for ultraviolet radiation detection by the spectral conversion

Abstract. It is shown that glass fibers doped with luminescent molecular clusters of silver, cadmium and lead chalcogenides, or copper (I) can be used for the efficient radiation conversion of ultraviolet (UV) radiation to the visible spectral region. The advantages of radiation trapping in fibers by the luminescent centers and of spectral conversion are discussed. The excitation and luminescence spectra of luminescent fibers are presented. Analysis of application areas of the luminescent glasses and fibers is performed. The construction of the sensitive element for sensor models for electrical spark and UV radiation detection is described. The characteristics of the models of sensors for electrical spark and UV radiation detection are presented.

Advances in photo-thermo-refractive glass composition modifications

The novel photo-thermo-refractive (PTR) glass developed in ITMO University is a very promising optical material for photonic and plasmonic applications. In this paper authors represent study of tin influence on photo thermo inducted crystallization process and make a comparison of the optical and holographic properties of the new and classic composition of glass. Also during this work was made overall optimization of chemical composition namely was optimized concentration of halides, fluorides, bromides which are responsible for crystalline phase properties. Ions of antimony, which playing key role in catching and transferring electrons emitted during the UV exposure and subsequent heating. Also was lowered the concentration of stray impurity ions which a capable to catch photo-electrons. Optical spectra show that new composition of PTR glass has no absorption band in visible range caused by metal nano particles of silver. That allows recording of pure phase holograms in wide spectral range. Furthermore new PTR glass allows receiving refractive index modulation up to 1500 ppm. And the UV exposures needed to achieve maximum changes in refraction index are 6-7 times lower than in classic glass.

Design and fabrication of optical devices based on new polyfunctional photo-thermo-refractive glasses

Novel optical elements and devices (holographic volume Bragg gratings, gradient optical elements, optical and plasmonic waveguides, hollow structures, thermo-and biosensors, phosphors for LEDs, down-converters for solar cells) have been designed and fabricated based on new polyfunctional photo-thermo-refractive glasses. Some technologies (photo-thermo-induced crystallization, holograms recording, laser treatment, ion exchange, chemical etching) have been used. Shown that photo-thermo-refractive glasses can be used as a basic optical material for many photonics applications with the characteristics comparable with other commercially available materials.

Latest achievements in chemical composition optimization of photo-thermo-refractive glass and its applications

Review on latest modification applappliedied to chemical composition of PTR glass was made. Advancements of updated chemical composition of PTR glass was shown in comparison with commercially produced glass. Such properties as refractive index change, optimal exposition and optical losses in visible range for the glass with recorded hologram was studied. In work samples of two chemical compositions were studied. Conditions of matching included equal regimes of thermal treatment and expose dosages as well as optimized parameters for each composition. Also the study of holograms received at optimal parameters for each glass was made on three different wavelengths. Moreover several new applications for holograms on a modified PTR glass were tested: such as holographic marks in telescopic systems and complex linked holograms. Due to high transparency in visible range, PTR glass now can be applied for creating holographic marks in telescopic systems. Studies show transparency of 92% with Fresnel losses. Also it is found that spectral selectivity is maintained for such holograms, thus it is opening a new way of optical solutions in telescopic systems. As it was measured, spectral selectivity of recorded hologram corresponds to 400mkm efficient thickness according to calculations. Though, it needs further studies to increase the effective thickness of such holograms as well as investigations of different Bragg angles at recording step. Complex (linked) holography is another way of multiplexing inside a bulk glass. It leads to combination of reflecting and transmitting Bragg gratings as a unite element with proper functions. This, for instance, can provide positive feedback for complexes of laser diode crystals on a small size site. Simultaneously, such element can combine emission from all emitting surfaces in one beam. This study may lead to creation of high power coherent diode laser sources at small size site with ultra-narrow emitting bandwidth and high quality spatial beam characteristics.

Spectral-luminescent Properties of Silver Clusters Formed in Ion-exchanged Antimony-doped Photo-thermo-refractive Glasses

Photo-thermo-refractive glasses are now attractive material for developing various elements and devices of photonics. Influence of antimony oxide content in the photo-thermo-refractive glass composition and subsequent heat treatment temperature on the spectral-luminescent properties of silver non-metal clusters and metal nanoparticles formed with low-temperature ion exchange method were studied. Silver clusters in ion-exchanged Sb-doped photo-thermo-refractive glasses reveal broadband and intense emission in the visible and near infrared ranges. Absolute quantum yield of luminescence reaches 63% (λex=365 nm), which opens up new prospects for using such materials as phosphors for white LEDs and down-convertors for