Results of investigations into the spectral and power characteristics of two-photon fluorescence of a liquid drop with the Rhodamine 6G dye irradiated by femtosecond laser pulses are presented. It is demonstrated that stimulated emission of two types is realized in drops with the concentrated dye solution, namely, superfluorescence within the drop volume and lasing on whispering gallery modes.Creation of laser systems capable of generating femtosecond light pulses with high intensity sufficient for realization of multiphoton effects in the process of radiation interaction with substance in the middle 80s stimulated the formation of a number of new directions of modern physics and technology. Among these are new methods of laser control over physical and chemical processes based on the selective multiphoton absorption of femtosecond radiation by substance molecules, including finely dispersed substance (femtochemistry) [1, 2]. Creation of highly informative optical communication channels in the atmosphere also posed the problem of studying the multiphoton interaction of femtosecond radiation with substance, in particular, with disperse media incorporating the atmospheric aerosol. Upgrading systems of optical information transfer and processing aimed at increasing their operation speed and compactness of optical elements makes urgent a study of femtosecond radiation interaction with such objects as microfibers and dielectric microresonators that can serve as miniature emitters or frequency converters [3,4].It should be emphasized that the above-mentioned objects -disperse media -exposed to femtosecond radiation are specific physical systems. Their specifics are that spherical particles have focusing properties and form high-Q microresonators in which morphological resonances or modes of whispering gallery are realized [5]. This results in a sharp increase in the intensity of acting optical fields in the particle volume and, as a consequence, in reduced power thresholds of nonlinear optical processes proceeding in particles. In spite of the fact that optical processes in spherical particles and drops have been investigated already during a quarter of the century, only few works study the interaction of multiphoton femtosecond radiation with the aerosol and liquid-drop substance.The present paper is aimed at studying fluorescence of drops with an organic dye excited due to the multiphoton absorption of femtosecond laser pulses.A titanium-sapphire laser generating pulses at the wavelength λ = 0.8 µm with duration t p = 80 fs and 9 ns and energy per pulse <17 mJ served as a source of femtosecond radiation [6]. The width of the radiation spectrum for nano-and femtosecond pulses at half-maximum was ~25 nm. The intensity distribution over the beam cross-section was close to Gaussian. The femtosecond pulse energy was controlled by registration of radiation in the reference channel with the help of a calibrated photodiode.Unfocused femtosecond radiation was directed onto a drop with the Rhodamin 6G dye in ethanol. The drop ...
The article deals with the problems of increasing the efficiency of electric separators through developing new approached to their design for upgrading of heat-treated crushed brown coal. The rational use of natural resources and efficient energy consumption are two basic requirements of EU Directive 2008/1/EC. It is expected that the techniques for brown coal pre-drying will result in increased energy efficiency of enterprises of up to 5% and upgrading of heat-treated brown coal will increase energy efficiency by the same value. To upgrade heat-treated brown coal it is necessary to design new equipment including high-efficiency electric separators. It was earlier found that the maximum value of coal particle charge was provided in a corona-electrostatic separator, a lower level of coal particle charge was observed in a triboelectrostatic separator and the lowest level of coal particle charge was established in a plate-type electrostatic separator. The basic efficiency constraint for drum-type corona-electrostatic separators is the diameter of a collecting electrode and one operating area. To select the directions for increasing the productivity and efficiency in separating heat-treated crushed brown coal in drum-type corona-electrostatic separators the results of studies of changes in force vectors affecting its charged particles, nature of their motion in the electric field resulting in separated productsorganic and mineral components of brown coal, taking this into consideration the factors of the heating temperature, voltage across a corona-producing electrode (drum), diameter of a corona-producing electrode and its rotation speed, have been analyzed. The increased efficiency of a drum-type CES with a slight increase in its weight is associated with removing a constraint from design parameters-the diameter of a collecting electrode (drum). It is realized through the change of orientation of a collecting electrode from horizontal to vertical.
We report on the experimental demonstration of considerable lowering of stimulated luminescence (lasing) threshold in R6G laser dye solution doped with metal agglomerates (Ag, Al, Ni) upon second harmonic of Nd:YAG-laser illumination. Due to strong structural coupling between individual nanoparticles, they may form fractal agglomerates providing an extreme optical pump-field enhancement near their complicated surface. For the first time, we have observed more than twofold increase in lasing efficiency of metal aggregated dye solution as compared to non-agglomerated monomeric metal nanocolloids. No random laser manifestation or surface plasmon-polariton resonances excitations were observed.
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