S. A. Ivanov

Holographic characteristics of a modified photothermorefractive glass

The spectral and holographic characteristics of classical and modified photothermorefractive glass are compared. It shows that modified photothermorefractive glass has no additional absorption bands in the blue–green region, as is the case in classical photothermorefractive glass. This makes it possible to record purely phase holograms in modified photothermorefractive glass. The refractive-index increment is a factor of 2 greater in modified photothermorefractive glass than in classical photothermorefractive glass.

Recording holographic marks for telescopic systems in photo-thermo-refractive glass

The basic possibility of forming a holographic image of a two-dimensional object mark in photothermo-refractive (PTR) glass is demonstrated. The parameters of a hologram in a three-dimensional medium are calculated, and a subsequent analysis of the characteristics of the recorded mark prototype is performed. The advantages are shown of PTR glass as a holographic medium in telescopic systems in comparison with existing analogs. Samples with high transmission in the visible spectral range (more than 85%) and high diffraction efficiency (more than 95%) are obtained that show all the effects inherent in holographic marks in existing telescopic systems.

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.

Narrowing of the emission spectra of high-power laser diodes with a volume Bragg grating recorded in photo-thermo-refractive glass

The spectral characteristics of a high-power semiconductor laser with an external cavity in which longitudinal-mode selection is implemented by means of a holographic volume Bragg grating recorded in photo-thermo-refractive glass are investigated. Mode selection leads to narrowing of the spectrum of the laser diode from an initial width of 6 nm to 5 Å. In the narrowed spectrum, a fine structure representing a set of eigenmodes that correspond to the length of a laser chip is resolved. The number of these modes is limited by the width of the spectral selectivity curve of the grating. It is shown that insertion of the grating into the cavity leads to severalfold enhancement of the grating selectivity. It is demonstrated that the implemented external-cavity design makes it possible to smoothly tune the laser emission wavelength in a 10-nm range.

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.

Analysis of the hologram recording on the novel chloride photo-thermo-refractive glass

In this research, we present new holographic material based on fluoride photo-thermo-refractive glass(PTR) - chloride PTR glass. One of the benefit of this type of PTR glass is positive refractive index change. During this work, for the first-time volume Bragg gratings were recorded in this kind of material. The first experiments revealed that such gratings are mixed i.e. possess both absorption and phase components. Complex analysis shows that both refractive index and absorption coefficient are modulated inside the grating structure. We found out that at first there is no strict dependence of the refractive index change from dosage, but as we continue the process of thermal treatment – dependence is appear. Exposure influence on the refractive index change for this glass differs from fluoride one and shows some sort of saturation after the exposure of 4-6 J/cm2 . We distinguished refractive index change and absorption coefficient change and observed both behavior with increasing thermal treatment time. We found out that the increase of thermal treatment time results in the significant refractive index change. At the same time the absorption does ‘not practically change. It was found that maximum modulation of refractive index is comparable with fluoride PTR glass and achieves value of 1600 ppm. The modulation of absorption is equal to induced absorption caused by silver nanoparticles and depends from reading wavelength. Our study shows that almost all absorption is modulated inside the grating.

A Holographic Prism Based on Photo-Thermo-Refractive Glass: Requirements and Possibilities

A technology for multivalued holographic measurement of a plane angle—a holographic prism, which serves as the basis for a device for calibrating the testing tools for navigational equipment under rolling— has been developed. The holographic prism is a miniature sample of photosensitive material, which contains a system of superimposed holographic gratings, and a laser the radiation of which passes through gratings to form a fan of diffracted beams. The fan in a prism based on a calcium fluoride (fluorite) crystal with color centers contained six out-of-plane beams radiating from a region with a hard-to-localize center. This fact hindered calibration of the measure and its application in the testing device. The use of photothermo-refractive glass as a material for preparing a sample and recording a system of holograms in it makes it possible to eliminate the drawbacks of fluorite-based prism. The number of holograms rises up to 21, the fan becomes in-plane, and its center is localized in a small region, with a size of several tenths of the sample thickness (1–2 mm). The fan beams are energetically homogeneous, and each can be identified when using the fan in a testing device.

Holographic prism based on photo-thermo-refractive glass

New application of photo-thermo-refractive glass (PTR) named “holographic prism” is presented. In the holographic prism angles between directions are set by the holograms which create “fan” of signal beams. This kind of prism creates several signal beams which are equal to the reflections from facets of the conventional silica prism. Implementation of PTR glass as a holographic medium for this device brought us several advantages and new features. First it leads to decrease in overall size of the prism that positively affects the identification process of the beams crosspoint. Thus, it increases sensitivity and accuracy of the measure. Second, greater value of the refractive index change in PTR glass in comparison with calcium fluoride crystal allows us to increase quantity of the recorded reference beams for the measure which leads to sensitivity increase. During this work, we established recording schedule for the PTR glass in case of the superimposed gratings recording. Was found that exposure for each grating should be equal to the 1/N fraction of the optimal exposure where N is the number of multiplexed gratings. We proved that in this case the total value of the refractive index modulation amplitude is equal to that for the single grating with optimal exposure. Considering obtained data we successfully performed recording of the holographic prism of the second modification with 14 channels.

Resonator free Er-Yb laser based on photo-thermo-refractive (PTR) glass

First step of Er-Yb laser based on PTR glass creation was made. Complex study of luminescent characteristics of PTR glass doped with Er-Yb with recorded holograms was made. Direct measurements of population inversion of main Erbium level 4I13/2 for different Erbium concentrations and pumping power was made. Was shown that spectral and luminescent characteristics of poly-functional PTR glass doped with Er-Yb and recorded holograms are comparable to the traditional laser barium phosphate glass.

Longitudinally diode pumped CW Er-Yb laser based on photo-thermo-refractive glass

For the first time CW laser oscillation on Er-Yb doped PTR glass with diode pumping is demonstrated. For the monolithic laser the maximum output power of 0.47W at wavelength of laser oscillation of 1574 nm and a slope efficiency of 6% was achieved.