Special features of the fluorescence of organic molecules with two-photon absorption in a drop upon exposure to a femtosecond laser pulse

Abstract

A closed system of equations for spherical microresonator modes and populations of energy levels of twophoton excited molecules placed in a resonator and exposed to a femtosecond laser pulse is derived. The threshold of transition of spontaneous emission into stimulated one (in the superfluorescence mode) in a microparticle is established with allowance for the microparticle morphology and laser pulse duration.

Theoretical description of the spectrum of emission of a droplet of ethanol solution of rhodamine 6G under femtosecond laser irradiation

“…The characteristics of the Stokes emission of dye solutions during femtosecond laser irradiation were studied experimentally in a series of works [1][2][3][4][5]. A spectral feature of the emission was observed for suffi ciently high dye concentrations and an experimental geometry providing the radiation focusing due to an ordinary lens [1] or the effects of focusing in a drop [2].…”

“…In this connection, we suggested a set of equations for spectral density of Stokes emission of matter from a droplet, describing spectrum formation in time dur ing the interaction of the droplet's matter with a fem tosecond laser pulse [3]. These equations were tested in the problem of the qualitative theoretical explana tion of the spectral singularity of the Stokes emission of Rhodamine 6G from an ethanol droplet after its irradiation by femtosecond laser pulses [3].…”

“…These equations were tested in the problem of the qualitative theoretical explana tion of the spectral singularity of the Stokes emission of Rhodamine 6G from an ethanol droplet after its irradiation by femtosecond laser pulses [3].…”

“…Such strong growth of the signal from the emitting droplet in a narrow spectral range in the blue part of the dye fluorescence spectrum can testify to the evolu tion of stimulated fluorescence or, in other words, of superfluorescence in the droplet's volume [2,3].…”

“…Some qualitative estimates of the superfluores cence evolution threshold are presented in [3]. How ever, it is required to set up the most complete corre spondence between the mathematical model sug gested for superfluorescence in [3] and the experimental data [2] in the context of the necessity of further theoretical study caused particularly by a recent series of the related experiments [15,16].…”