Oleg B. Danilov

Nonlinear-optical laser-radiation limiters

This article describes nonlinear-optical laser-radiation limiters based on fullerenes and fulleroid and semiconductor nanostructures. It is shown that limiters based on such nonlinear-optical media make it possible to limit the laser radiation to a level that is safe for eyes and semiconductors in the visible, near-, and mid-IR regions in a wide range of laser-pulse widths.

Nonlinear optical limiters of laser radiation based on reverse saturable absorption and stimulated reflection

We presented wide range of laser-radiation optical limiters that are based on different physical principles, operating in 400-12000 nm spectral range with rate 100-1 ns and providing wide dynamic range of limiting required for eye and sensor protection. We propose and investigate a method for reduction of the optical limiting threshold due to the Bragg reflection in a system with distributed feedback. The limiting threshold with the Borman effect, accompanying by diffractional absorption suppress and stimulated reflection from the LC Bragg grating, is about (mu) J/cm2 for nano seconds pulse. We investigate nonlinear optical limiters of laser radiation based on fullerene-contained materials, operating on the basis of reverse saturable absorption (RSA) as well as stimulated nonlinear reflection of laser radiation. Fullerenes C60, C70 and C84 were studied with the second harmonic of Nd:YAG laser, 532 nm, single-mode radiation pulses of 30 ns duration and maximum energy 0.35 J. Definite thresholds of RSA limiting vary from 0.05 to 0.1 J/M2) depending on fullerene density and limiting scheme. Dynamic range of limiting sufficiently increases for multi-pass trains, the fluence decreases up to 10000 times. We elaborate 3000-12000 nm laser-radiation attenuators based on multi-layer interference containing vanadium-dioxide film. It is shown that these attenuators can operate due to both amplitude and diffraction effect. Attenuation is up to 1x103- 1x105 times for 1 MW/cm2 beams, operating time being 30-100 ns. For sensors in cooled optical systems, radiation attenuators can be used with vanadium oxides having the phase transition at cryogen temperatures.

Converting solar energy into laser radiation using a fullerene-oxygen-iodine laser with solar pumping

The concept of a system for directly converting solar energy into laser radiation on the basis of a fullerene-oxygen-iodine laser has been developed. It is shown that this system has advantages and is competitive with other similar solar-energy-conversion systems. Various versions of singlet-oxygen generators based on solid-phase fullerene-containing structures are analyzed. Based on this analysis, it is concluded that such a generator needs to be operated with molecular oxygen passing through a porous fullerene-containing coating deposited on a substrate with a porous structure to compensate the loss of oxygen in the coating as it undergoes photodesorption. Experimental research into the processes of solar-energy conversion into laser radiation has been carried out, using a prototype that has been developed of a fullerene-oxygen-iodine laser with pumping by a solar-radiation simulator. Lasing in the pulsed-periodic regime of laser operation has been obtained, with repetition rate 10Hz and mean output power 30W. Lasing energy per unit volume of the active medium of 9J/L has been achieved.

Singlet-oxygen generator on base of solid-state fullerene-containing structures for fullerene-oxygen-iodine laser design: physical principles

The singlet oxygen generator development is the basic problem of fullerene oxygen iodine laser design. Physival principles of singlet oxygen generator on the base of solid-state fullerene-containing structures were investigated. The solid-state singlet oxygen generator is a surface of membranous structures with embedded fullerenes (fullerites) of fullerene-like nanostructures - astralenes. Singlet oxygen is generated by interaction of molecular oxygen, sorbed by the surface and fullerene-like nanostructures, photoexcited by optical pump. The singlet oxygen entrance in gas phase occurs as a desorption wave, caused by surface heating by optical pump. The effectiveness of molecular oxygen sorption by fullerene C60 and astralen depending on temperature, the extent of nanostructures heating, oxygen pressure and morphology of coating was studies.

Nonlinear-optical limiters of laser radiation based on suspensions of carbon and fulleroid nanoparticles

The mechanisms of nonlinear-optical limitation in suspensions of carbon and fulleroid nanoparticles have been studied experimentally and theoretically. The study was carried out in the wide spectral range of 300-1064 nm. Suspensions of fulleroid nanoparticles - astralenes - have proven to be more promising in a number of parameters (the limitation efficiency, the possibility of multiple use).

Photodynamics of nonlinear fullerene-containing media

The results of theoretical and experimental studies on photodynamics and mechanism of nonlinear optical processes, responsible for optical limiting of power radiation in the wavelength range from 0.3 to 1.3 microns, are presented. Peculiarities in the mechanisms of optical limiting for different fullerene-containing matrices, including solutions, solid-state and polymer systems, are shown.

Possibility of realizing fullerene-oxygen-iodine laser with solar pumping (sun-light FOIL)

We consider the possibility to design the fullerene-oxygen- iodine laser with optical pumping (solar, particularly). It is assumed that singlet oxygen is formed at pass of molecular oxygen through (and interaction with) mixture of lower and higher fullerenes in the triplet metastable state obtained at illumination of fullerenes. The presented results of estimates by a photokinetic model show the opportunity to reach the efficiency of the FOIL with solar pumping at the level of several tens of percents. We present the results of experimental and theoretical studies of singlet oxygen yield at interaction of optical pumping with fullerene in solutions. Laser radiation with wavelength of 532 nm and wideband lamp radiation for imitation of solar radiation were used as pumping.

Solid-phase fullerene-like nanostructures as singlet oxygen photosensitizers in liquid media

Singlet oxygen generation by fullerene and astralen containing surfaces and powders under visible irradiation was studied in water and organic liquids by means of 1Δg state luminescence and chemical scavenger transmittance measurements. The chemical method, pioneered for solid photosensitizers of 102, allowed to measure the singlet oxygen concentration in the aqueous medium down to 108 cm-3. The singlet oxygen sensitizing by the solid-phase fullerene-containing systems was found to be 100 times less effective then by fullerene in solution. The results obtained confirm the applicability of these structures in biology and medicine.

Fullurene-oxygen-iodine laser (FOIL): physical principles

The paper considers the physical principles of developing the fullerene - oxygen - iodine laser (FOIL) with optical (sunlight in particular) pumping. Kinetic scheme of such a laser is considered. It is shown that the utmost efficiency of FOIL may exceed 40% of the energy, absorbed by fullerenes. Presented are the experimental results of singlet oxygen generation in liquid media (solutions and suspensions) and in solid-state structures, containing either fullerenes or fullerene-like nanopartickles (FNP). In experiment was shown the possibility of the singlet oxygen transfer to the gaseous phase by means of organizing of the solution (suspension) the boiling as well as of the gasodynamic wave of desorption from the solid-state structures, containing fullerenes or FNP. We present the preliminary experimental results of pulsed generation in optically pumped FOIL with the use of primary photodissociation of iodide for preparation of the atomic iodine in the generation zone. In the experiments on FOIL generation was implemented the principle of spectral separation of optical pumping.

Fullerene-oxygen-iodine laser (FOIL): physical principles

The paper considers the physical principles of developing the fullerene —oxygen — iodine laser (FOIL) with optical (sunlight in particular) pumping. Kinetic scheme of such a laser is considered. It is shown that the utmost efficiency of FOIL may exceed 40% of the energy, absorbed by fullerenes. Presented are the experimental results of singlet oxygen generation in liquid media (solutions and suspensions) and in solid-state structures, containing either fullerenes or fullerene-like nanopartickles (FNP). In experiment was shown the possibility of the singlet oxygen transfer to the gaseous phase by means of organizing of the solution (suspension) the boiling as well as of the gasodynamic wave of desorption from the solid-state structures, containing fullerenes or FNP. We present the preliminary experimental results of pulsed generation in optically pumped FOIL with the use of primary photodissociation of iodide for preparation of the atomic iodine in the generation zone. In the experiments on FOIL generation was implemented the principle of spectral separation of optical pumping.