Fluorescence of a Liquid Drop with a Dye Excited by Femtosecond Laser Pulses

Abstract

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 ...

Sound generation in the atmosphere upon exposure to high-power milli- and microsecond laser pulses

“…For laser energy densities less than this threshold value, the atmospheric aerosol does not change its phase state, and acoustic radiation is generated due to the thermal expansion of the HPLR propagation channel (the thermooptical mechanism of sound pulse generation). Experimental and theoretical investigations into the mechanisms of acoustic wave generation in the atmosphere upon exposure to laser radiation and the special features of acoustic pulses from solid and liquid aerosol particles have been performed at the Institute of Atmospheric Optics of the Siberian Branch of the Russian Academy of Sciences since 1980 [1- 20,22,23,[27][28][29][30][31][32][33][34]41]. A brief review of experimental and theoretical works on laser-induced shock waves through 1990 was presented in [16].…”

Characteristics of the angular intensity distribution of the multiphoton fluorescence excited in spherical drops

“…Many works (for example, see [3,4]) were devoted to experimental studies of the multiphoton fluorescence of liquid aerosol particles upon exposure to femtosecond laser radiation. The results of studying the spectral and energetic characteristics of two-photon fluorescence of rhodamin 6G in large ethanol drops (the drop sizes did not exceed 2 mm) upon exposure to femtosecond laser pulses were presented in [3].…”

“…The results of studying the spectral and energetic characteristics of two-photon fluorescence of rhodamin 6G in large ethanol drops (the drop sizes did not exceed 2 mm) upon exposure to femtosecond laser pulses were presented in [3]. A Ti:Sapphire laser generating pulses at a wavelength of 0.8 μm with duration t s = 80 fs and 9 ns served as a femtosecond radiation source with energy per pulse <17 mJ.…”

<title>Multiphoton excitation of fluorescence in spherical particles: angular distribution of scattered radiation</title>

“…Experimental investigation of multiphoton fluorescence of liquid aerosol particles exposed to femtosecond laser radiation is considered in [3,4]. The study of spectral and power characteristics of the two-photon excited fluorescence of Rhodamine 6G dye in large ethanol drops (drop size no larger than 2 mm) exposed to laser pulses of femtosecond duration is presented in Ref.…”

“…The study of spectral and power characteristics of the two-photon excited fluorescence of Rhodamine 6G dye in large ethanol drops (drop size no larger than 2 mm) exposed to laser pulses of femtosecond duration is presented in Ref. 3. A Ti:Sapphire laser emitting pulses at a wavelength of 0.8 µm with a duration t p =80 fs and 9 ns at a pulse energy <17 mJ served a source of femtosecond radiation.…”