V. B. Shilov

The optical limitation effect and features of luminescence kinetics in hybrid nanosystems with CdSe/ZnS quantum dots and organic agents

The optical limitation effect in three-component systems formed in colloidal solutions of semiconductor CdSe/ZnS quantum dots with participation of fullerene C60 and perylene, has been experimentally investigated. The first and second harmonics of a YAG:Nd3+ laser operating in the single-shot mode with a pulse duration of 7 ns and laser pulses subjected to stimulated Brillouin scattering (SBS)-stimulated Raman scattering (SRS) compression with a duration of about 20 ps near 560 nm have been used as radiation sources. It is shown that the optical limitation efficiency in the systems studied is determined by electron transfer. This is confirmed by the analysis of luminescence quenching.

Light quenching and dark states in colloidal solutions of semiconductor CdSe/ZnS quantum dots

The photodynamics of optical limiting in colloidal solutions of different-size CdSe/ZnS quantum dots is studied. The behavior of the dependences points to a multistage process that includes the bleaching and optical limiting stages. The limiting photodynamics is compared with luminescence dynamics of quantum dots under conditions of high-power excitation. It is shown that the optical limiting efficiency in such media is determined by the position of exciting radiation with respect to the main exciton absorption band of the quantum dot. The roles played by so-called dark states and light quenching in limiting photodynamics are discussed.

Absorption and emission dynamics in concentrated optical ensembles under laser excitation

A new theoretical model describing the emission and absorption dynamics in an ensemble of molecules under intense coherent pulsed pumping is developed on the basis of the concepts of cooperative light-induced luminescence (CLIL). The CLIL development is described within the framework of formalism of the system density matrix in the space of photon wave functions. It is shown that the fast growth of CLIL relates to the development of coherent states of the quantum field in the area of efficient cooperative interactions of molecules (coherence volume). A system of equations for the calculation of CLIL energy, population of excited states, and optical absorption of the system in dependence on the laser pump energy density is solved. The theoretical results obtained are in good agreement with the experimental data.

Optical properties of vanadium dioxide nanoparticles in nanoporous glasses

Nanoparticles of vanadium dioxide have been synthesized in nanoporous silicate glasses with a pore size of 7 and 17nm. Static temperature hysteresis loops of the transmittance, corresponding to the semiconductor-metal phase transition in the vanadium dioxide nanoparticles, have been obtained at a wavelength of 1.15μm. The nonlinear-optical response of the nanoparticles has been measured in the visible and near-IR regions for picosecond laser pulses. The variation of the optical properties of nanoparticles in the pores of the glass at the semiconductor-metal phase transition has been numerically modelled.

Low-dispersion optical fiber highly transparent in the UV spectral range

The National Ignition Facility performs fusion experiments using ultraviolet (351 nm) light. High-bandwidth, low-attenuation optical fibers are required to transport subnanosecond, UV laser diagnostic signals from the target chamber area to recording instruments located in adjacent rooms, with some fiber runs approximately 65 m in length. Special optical fibers are developed and fabricated to perform this task, since no existing commercially available fibers possess all of the required characteristics. These large-core (435 µm) fibers have optical dispersions less than 0.9 psec/m and attenuations less than 150 dB/km at 351 nm.

Optical limiting of laser radiation and light quenching in colloidal solutions of CdSe/ZnS semiconductor quantum dots and hybrid systems

The photodynamics of power optical limiting is studied in colloidal solutions of quantum dots by exiting the system in the absorption band with 0.4-ns 532-nm pulses. Based on a parallel analysis of the dependence of the nonlinear transmission and luminescence decay kinetics of the investigated solutions, the conclusion is drawn that the main mechanism of the optical limiting of nanosecond laser radiation pulses is light quenching of the so-called dark states in quantum dots. The efficiency of limiting is determined by the dynamics of the population of these states. It is shown that CdSe/ZnS QDs–C60 hybrid system has the same efficiency in both the single-pulse and 10-Hz reptation rate modes.

Enhancement of the quantum efficiency of a fluorescence cesium filter

The dependence of the quantum efficiency of fluorescence cesium vapor filters, which allow one to select with a high contrast the desired narrow-band signal against the background of broadband (solar) radiation, is studied. The most important characteristic of such filters, apart from the spectral band, is the quantum efficiency; i.e., the ratio of the number of florescent photons to the number of absorbed photons of excitation. It is experimentally shown that addition of a buffer gas to working cesium atoms can substantially increase the quantum efficiency as compared with that of working atoms in vacuum. The dependence of the quantum efficiency on the characteristic of transitions that are involved in population of atomic levels from which fluorescence occurs, and the processes resulting in an increase in the quantum efficiency of atomic fluorescence filters are considered.

Development and production of UV and VUV sources

This paper discusses gas-discharge sources of ultraviolet and vacuum ultraviolet radiations developed at the S. I. Vavilov State Optical Institute. The main characteristics of lamps with arc, glow, rf, and barrier discharges are presented, along with areas in which they can be used. It is indicated that krypton, xenon, argon, hydrogen, deuterium, neon, helium, and combinations of these gases are used as a fill gas. It is pointed out that a recent breakthrough in VUV engineering was to use magnesium fluoride and lithium fluoride windows. After the technique for attaching windows made from these materials to glass bulbs was mastered, it became possible to create a new class of VUV sources. It is emphasized that the structure of the laboratory of gas-discharge light sources assumes that the development of new types of UV and VUV lamps is to be combined with their production. This makes it possible to carry out small-scale production and to develop and fabricate sources (lamps) as single samples to meet individual technical requirements, and this is important when developing new devices that use UV and VUV radiation sources.

Narrow-band fluorescence filters based on cesium vapor

The characteristics of narrow-band atomic fluorescence filters intended for separating out the useful signal on the background of broad-band noise radiation have been studied. Cesium vapors in a vacuum chamber and with additives of buffer gases are used as the working medium of the filters. It is shown that, under certain conditions, adding a buffer gas increases the quantum efficiency.

Effect of cooperative interactions in optical ensembles on the threshold characteristics of lasing in the case of coherent optical pumping

The dependence of the threshold pump energy of dye lasers on the quantum yield of fluorescence of active solutions in the case of laser excitation was studied. The rate of increase in the threshold pump energy was found to be considerably lower than the rate of decrease in quantum yield. The results were interpreted in terms of the development of the cooperative interaction between active centers in the high-intensity coherent pump field.