E. N. Sosnov

A jet-type singlet oxygen generator based on porous fullerene-containing structures

The results of studying the efficiency of singlet oxygen generation under optical pumping of solid-state fullerene-containing structures in a wide range of experimental conditions are presented. A description of a singlet oxygen generator based on porous fullerene-containing structures optically pumped by a light emitting diode (LED) matrix and enabling a continuous molecular oxygen flow through the porous substrate structure onto the irradiated fullerene surface is provided.

Direct optical excitation of singlet oxygen in organic solvents

Efficient excitation of singlet oxygen is demonstrated for several organic solvents (CS2, CCl4, and C6F14) that are irradiated using LED in the visible spectral range in the absorption bands of the O2-O2 collision complexes at the corresponding cooperative transitions. It is shown that the two-photon interaction of the pumping radiation in the Herzberg I band of molecular oxygen with its excitation to the 3Σu+ state and the subsequent collisional relaxation to the 1Σg and 1Δg singlet states contributes to the excitation of singlet oxygen.

Observation of the luminescence of singlet oxygen at λ = 1270 nm under LED irradiation of CCl4

The efficiency of singlet-oxygen generation under optical pumping of oxygen dissolved in CCl4 has been analyzed using light-emitting diode arrays at three wavelengths (465, 525, and 625 nm), with direct recording of singlet-oxygen luminescence from the volume of irradiated solvent. The results obtained are compared with the efficiency of singlet-oxygen generation using C60 dissolved in CCl4 as a photosensitizer; it is shown that the efficiencies of singlet-oxygen generation differ by four orders of magnitude (on average) for only the radiation at the input of the solvent volume under study. The quantum yield of singlet oxygen upon direct optical excitation is about unity with respect to the optical-pump radiation absorbed in the solvent volume.

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.

Advancement and problems of fullerene-oxygen-iodine laser

The methods of improving the efficiency of a fullerene-oxygen-iodine laser are investigated. In the course of this research, we developed new fullerene coatings that possess better mechanical and radiative hardness, as well as higher efficiency of singlet oxygen generation. We show that, by using these coatings, the energy yield per unit volume of the active medium can be increased to 9 J/l, which is almost two times higher than the previous result. The energy efficiency of the laser can also be increased by a factor of nearly two. At the same time, several problems were revealed that hinder the further improvement of the laser efficiency and its long-term operation with stable parameters of the output radiation. We outline principal approaches to further optimization of the laser design that would help to overcome the negative factors and make it possible to create a fullerene-oxygen-iodine laser with high and stable parameters of the output radiation.

Spatial and temporal characteristics of TEA-CO2 laser action with intracavity vanadium dioxide mirrors

In a laser with the cavity, formed by the mirrors with thermal non-linearity, in some conditions the moving transverse spatial structures can occur. In this report, on the base of computer simulation, the analyses of dynamics of such structures have been performed for two cases: for the cavity with one non-linear mirror with dR/dT > 0 and for the conjugate cavity with two non-linear mirrors which have dR/dT of different signs. In the example of TEA-CO2 laser with light-controlled vanadium dioxide mirrors, we have shown that in the first case intracavity interaction of radiation with the non-linear mirror makes possible the control of shape and duration of leading edge of laser pulse and laser mode composition. In the second case one can obtain the regime of directed movement of laser action region with the velocity of 5 - 50 mm/microsecond(s) , which can be used in scan laser systems. The influence of optical and thermal parameters of non-linear mirrors on the laser action dynamics is discussed.

Effect of oxygen and iodine on the optical and magnetic properties of fullerite C60

The effect of oxygen and iodine on the optical and magnetic properties of fullerite C60 is studied by luminescence and EPR spectroscopy within widely varied experimental conditions (temperature of the medium, oxygen or buffer gas pressure, concentration of iodine vapor). It is demonstrated that the efficiency of the singlet oxygen formation when a fullerene sample is irradiated by a neodymium laser at a wavelength of 532 nm and the amplitude of the EPR signal emitted from the unirradiated sample are strongly affected by the concentrations of both oxygen and iodine vapor sorbed by the fullerene sample, as well as by its surface temperature. The spin-spin and spin-lattice relaxation times of paramagnetic centers in fullerite samples studied in the presence of molecular oxygen are determined by the method of microwave radiation absorption saturation.

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.

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.