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 ...
Abstract. The primary objective of this complex aerosol experiment was the measurement of microphysical, chemical, and optical properties of aerosol particles in the surface air layer and free atmosphere. The measurement data were used to retrieve the whole set of aerosol optical parameters, necessary for radiation calculations. Three measurement cycles were performed within the experiment during 2013: in spring, when the aerosol generation is maximal; in summer (July), when atmospheric boundary layer altitude and, hence, mixing layer altitude are maximal; and in late summer/early autumn, during the period of nucleation of secondary particles. Thus, independently obtained data on the optical, meteorological, and microphysical parameters of the atmosphere allow intercalibration and inter-complement of the data and thereby provide for qualitatively new information which explains the physical nature of the processes that form the vertical structure of the aerosol field.
This paper presents the results of experimental investigations into the interaction of laser pulses of femtosecond duration with aerosol having various composition (aqueous aerosol, dye solution with embedded nanoparticles), as well as with individual particles in the case of two-photon induced stimulated fluorescence. The acoustic method was employed to study the decay ofthe energy ofthe filament generated at different focusing, as well as the transmittance of the filament energy as it passed through the aerosol layer.
Greenhouse gas concentrations are increasing over the past few decades, creating the need to measure their concentration with high accuracy, including for determining their trends, sources, and sinks. In this regard, various methods of regional and global control are being developed. One of the measuring methods is passive satellite method, but they allow for you to get data mainly during the day and outside the poles of the Earth. Another method is active lidar; they require the consideration of various aspects that are related to the technical characteristics of the lidar and methods for solving inverse problems. This article discusses the possibility of using lidars for sensing carbon dioxide from space (orbit 450 km) and from a height of 10 km and 23 km, which presumably corresponds to the aircrafts and balloons. As a method of solving the inverse problem, the method of fully connected neural networks with three layers and pre-training of first layer is considered, allowing for the application of additional data, including the IPDA (Integrated Path Differential Absorption) signal, the scattered DIAL (Differential Absorption Lidar) signal, temperature, and pressure profiles. These estimates show the possibility of measuring the average concentration from an orbit height of 450 km with an error of 0.16%, a resolution of 60 km, with a 50 mJ laser pulse energy, and 1 m diameter telescope. It is also shown that it is possible to obtain the concentration profile, including the near-surface concentration with an error of 2 ppm.
We report on experiments on the interaction of a gigawatt femtosecond laser pulse train with hanging isolated millimeter-sized water droplets. A transparent droplet experienced explosive boiling-up and emitted light in the visible spectrum as a result of laser-induced plasma formed inside the droplet volume. The droplet emission spectra showed remarkable broadening, depending on the laser power. The role of pulse self-phase modulation in measured spectral broadening when the pulse propagates through the droplet is discussed.
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