I. M. Belousova

Theoretical investigation of nonlinear limiting of laser radiation power by suspensions of carbon particles

The effect of nonlinear limiting of laser radiation power by aqueous suspensions of carbon particles is analyzed by solving the equations of heat conduction, hydrodynamics, and phase transition dynamics self-consistently with the problem of light scattering, absorption, and passage through an extended medium. The results of computer simulation and experiments are compared.

Photoinduced quenching of the luminescence of singlet oxygen in fullerene solutions

The photoinduced quenching of the luminescence of singlet oxygen in solutions of C60 and C70 fullerenes in CCl4 is studied. It is shown that intense pumping of the solutions by ultraviolet and visible radiation leads to formation of relatively long-lived fullerene-oxygen complexes, which are effective quenchers of the 1Δg excited state of singlet oxygen. The behavior of these complexes depending on the experimental conditions (pumping intensity, concentration of fullerenes in the solution, and temperature) is studied. Decomposition of complexes with time is investigated. It is shown that, upon formation and gradual degradation of these complexes, the absorption spectra of the solutions change with time. The C60 fullerene is shown to be more stable to the intense pumping, its concentration being completely restored with the decomposition of the complexes. At the same time, C70 fullerene is partly irreversibly lost and the solution does not reach its initial concentration after decomposition of complexes.

Comparative studies of optical limiting in fullerene and shungite nanocarbon aqueous dispersions

Optical limiting properties of natural carbon nanoparticles (Shungite carbon) and fullerene aggregates in aqueous dispersions were for the first time studied and juxtaposed. For the picosecond laser pulses both dispersions exhibited comparable optical limiting property, apparently due to nonlinear absorption (mainly TPA). In the domain of the nanosecond laser pulses, nonlinear scattering NLS is thought to be main optical limiting mechanism in the dispersions under study. Shungite carbon dispersion showed stronger optical limiting (being similar to CBS) in visible and IR, which we ascribe to its structure more favorable to the thermal relaxation processes responsible for the NLS mechanism.

Structural and optical properties of solid-phase singlet oxygen photosensitizers based on fullerene aqueous suspensions

The relationship between the structural and photosensitizing properties of solid-phase particles of fullerene C60 in aqueous suspensions is studied using the methods of absorption spectroscopy, electron spin resonance spectroscopy (ESR), X-ray diffraction, and spectrophotometry of solutions of singlet oxygen chemical traps—histidine in combination with p-nitrosodimethylaniline. Two new variants are proposed for obtaining aqueous suspensions of particles of solid-phase fullerene whose structures are disordered and whose degrees of amorphization are 67 and 40%, respectively. It is shown that an increase in the disorder of the structure of particles in suspensions and a decrease in their average size facilitate an increase in the formation efficiency of singlet oxygen by solid-phase fullerene presumably due to an in increase in the concentration of surface localized excitons.

A mathematical model of the photodynamic fullerene-oxygen action on biological tissues

A kinetic model of the photodynamic fullerene-oxygen action on biological tissues is developed. The efficiency of generation of singlet oxygen is studied in relation to the intensity of exciting radiation and the concentrations of fullerene and oxygen. The spectral efficiencies of singlet oxygen generation upon irradiation of a biological tissue by a lamp and different lasers are studied and compared with each other. The power of luminescence of singlet oxygen is calculated. The spatial distributions of singlet oxygen in allantoic fluid and in murine sarcoma are studied. The oxidation of lipids of external membranes is assumed to be the basic mechanism of cell damage. The characteristic time of this oxidation is calculated. The dose curve of cell survival is estimated. The results of modeling are compared with experimental data in the literature.

Photostability of a C60 fullerene coating as a solid-phase photosensitizer of singlet oxygen

The stability of the optical properties and the generation efficiency of singlet oxygen of a solidphase photosensitizer based on fullerene in an aqueous suspension subjected to prolonged intense irradiation with visible light are studied in comparison with a photosensitizer based on methylene blue in an aqueous solution. Changes in the absorption spectra show that, as a result of 20-min irradiation, the content of fullerene decreases by 2% from its initial value, while that of methylene blue decreases by 19%. In both cases, the dynamics of the decrease in the photosensitizing ability of the photosensitizers in the course of their irradiation correlates with the changes in their spectra, but the magnitude of this decrease in the case of the solid-phase photosensitizer is greater than the magnitude of its spectral changes because of the surface nature of the photosensitization process. The study of the absorption spectra of fullerene coatings shows that their irradiation in water or in air causes the same photodegradation of fullerene. At the same time, studies with the help of the electron spin resonance (ESR) technique reveal differences in the nature of processes undergone by fullerene in water and in air.

Lasing of iodine in the fullerene-oxygen-iodine system

The possibility of lasing in the fullerene-oxygen-iodine system with optical excitation of fullerene is studied. Laser radiation with an energy of 25 mJ and a pulse duration of 5–10 ms is obtained.

The possibility of controlling the optical limiting effect by a weak light signal

When investigating the nonlinear transmission of fullerene-doped π-conjugate organic structures, it has been found for the first time that the broad-band light of a flashlamp has considerable impact on the optical limiting of infrared laser emission (λ=1315 nm).

Modules for protecting the eyes from laser radiation in observational devices

This paper presents the results of the development of modules for protecting the eyes from laser radiation in the visible and near-IR regions. A description is given of a nonlinear-optical module with a medium based on a suspension of carbon nanoparticles in a silicone liquid, a multispectral interference filter having narrow reflection bands with minimal transmission at wavelengths of 355, 532, and 1064 nm, and a system adequate for observational devices with embedded protective elements. The combined use of the protective modules makes it possible to reduce the energy at the output of the system to a level no greater than 200 pJ when the input energy is 50 mJ and the pulse-repetition rates are as much as 10 Hz, thus ensuring the safety of the observer’s eyes.

Oxygen adsorption by fullerenes and carbon nanostructures

The dependences of oxygen sorption on time, gas pressure (up to 760 torr), and sample temperature were determined experimentally for three adsorbents (fullerene, astralene, and activated carbon). The difference in their adsorption abilities was shown to be related to the special features of their structures, primarily to the differences in surface area and pore volume. This conclusion was substantiated by X-ray studies of the structure of the powders. The characteristic heats of adsorption, specific surface areas, pore volumes and sizes, and characteristic energies of adsorption, which are responsible for the sorption properties of the adsorbents studied, were determined.