Vavilov State Optical Institute

About: Vavilov State Optical Institute is a facility organization based out in Saint Petersburg, Russia. It is known for research contribution in the topics: Laser & Holography. The organization has 1884 authors who have published 2648 publications receiving 21682 citations.

Homogeneous crystal nucleation in silicate glasses: A 40 years perspective

Abstract: We review a plethora of relevant experimental results on internal homogeneous crystal nucleation in silicate glasses obtained in the last four decades, and their analyses in the framework of the classical nucleation theory (CNT). The basic assumptions and equations of CNT are outlined. Particular attention is devoted to the analysis of the properties of the critical nuclei, which, to a large extent, govern nucleation kinetics. The main methods employed to measure nucleation rates are described and the possible errors in the determination of the crystal number density (and, correspondingly, in nucleation rates) are discussed. The basic regularities of both time and temperature dependencies of nucleation rates are illustrated by numerous experimental data. Experimental evidence for a correlation between maximum nucleation rates and reduced glass transition temperatures is presented and theoretically justified. Special attention is given to serious problems that arise in the quantitative description of nucleation rates when using the CNT, for instance: the dramatic discrepancy between calculated and measured nucleation rates; the high value of the crystal nuclei/melt surface energy, σcm, if compared to the expected value estimated via Stefan’s rule; the increase of σcm with increasing temperature; and the discrepancies between the values of the surface energy and the time-lag for nucleation when independently estimated from nucleation and growth kinetics. The analysis of the above mentioned problems leads to the following conclusion: in contrast to Gibbs’ description of heterogeneous systems underlying CNT, the bulk thermodynamic properties of the critical nuclei generally differ from those of the corresponding macro-phase resulting simultaneously in significant differences of the surface properties as compared with the respective parameters of the planar interfaces. In particular, direct experimental evidence is presented for compositional changes of the crystal nuclei during formation of the critical nuclei and their growth from critical to macro-sizes. In addition, detailed examinations of crystal nucleation and growth kinetics show a decrease of both the thermodynamic driving force for nucleation and of the critical nuclei/liquid interfacial energy, as compared with the respective properties of the macro-phase. However, despite significant progress in understanding crystal nucleation in glasses in the past four decades, many problems still exist and this is likely to remain a highly interesting subject for both fundamental and applied research for a long time.

Polarized alkali-metal vapor with minute-long transverse spin-relaxation time.

Abstract: We demonstrate lifetimes of Zeeman populations and coherences in excess of 60 sec in alkali-metal vapor cells with inner walls coated with an alkene material. This represents 2 orders of magnitude improvement over the best paraffin coatings. We explore the temperature dependence of cells coated with this material and investigate spin-exchange relaxation-free magnetometry in a room-temperature environment, a regime previously inaccessible with conventional coating materials.

Effect of ZnS shell thickness on the phonon spectra in CdSe quantum dots

Abstract: The evolution of the optical phonon spectra of colloidal core/shell CdSe/ZnS quantum dots with an increase of the shell thickness from 0.5 to 3.4 monolayers has been studied by resonant Raman spectroscopy. The results obtained suggest that the ZnS shell changes its structure from amorphous to partly crystalline as the thickness increases. Simultaneously, an increase in Raman scattering by surface (core/shell interface) phonons and the redshift of the corresponding phonon band have been observed and assigned to variations in the shell structure. The disorder present in the shell provides a major contribution to the line shape of the Raman spectra at higher ZnS coverage. A method to control the quality of quantum dots based on Raman spectroscopy is proposed.

IR fundamental spectra and structure of pyrophosphate glasses along the 2ZnO·P2O5–2Me2O·P2O5 join (Me being Na and Li)

Abstract: The IR reflection spectra of mixed zinc alkali pyrophosphate glasses in the broad frequency ranges are reported and the quantitative treatment of these with a version of the dispersion analysis method was conducted based on the specific analytical model of the complex dielectric constant of glasses. Numerical data on the optical constants, band frequencies, and band intensities are calculated. Results obtained are interpreted in terms of vibrations of the (PO3)2− and (PO2)− terminal groups, (PO4)3− anion, and P–O–P bridge. The presence of all these groups in the structures of glasses under study is confirmed and the formation of the (P3O9)3− ring metaphosphate anion rather than the chain polymeric phosphate anions is suggested. The gradual decrease in the width of the anion distribution toward the pyrophoshate anion with the Me2O for ZnO substitution is also confirmed. It is shown that this decrease determines the IR spectrum variations observed in the 0 to about 27 mol% Na2O composition range. The amounts of the (PO4)3− and (P3O9)3− anions are shown to become negligible in the structures of glasses with Na2O content greater than 30 mol%, and the IR spectrum variations observed in the 27–45 mol% Na2O composition range are shown to be mostly due to the intensity redistribution from the low-frequency component of the asymmetric stretch of the (PO3)2− terminal group to the high-frequency component of the same stretch.

Laser and nonlinear properties of the potassium gadolinium tungstate laser crystal KGd(WO4)2:Nd3+-(KGW:Nd)

Abstract: S. I. Vavilov State Optical InstituteState Research CenterScientific Research and TechnologicalInstitute of Optical Materials ScienceSt. Petersburg 193171, RussiaAbstract. The mechanical, thermophysical, spectroscopic, nonlinear,and laser properties are presented for one of the most efficient lasercrystals: neodymium-doped potassium gadolinium tungstate,KGd(WO