Single- and two-phonon excited fluorescence of liquid aerosol. Dependence on fluorophore concentration at different laser intensities

The fluorescence pattern of rhodamine 6G from a liquid aerosol was studied experimentally with varying concentration of the fluorophore irradiated by nanosecond laser pulses with a wavelength of 1.06 μm. A dependence of the fluorescence signal in the “backward” direction on the concentration of R6G molecules was found: with an increase in the fluorophore concentration from 10-2% to 5% in an ethanol solution, a decrease in the fluorescence intensity by almost two times is observed for both single-photon-excited fluorescence and two-photon fluorescence. The fluorescence signal increases with increasing pump energy. At high dye concentrations, signal saturation with increasing pump energy is observed for single-photon excited fluorescence. For two-photon fluorescence, the energy dependence is preserved even at high concentrations. The dependence of the fluorescence radiation pattern shape at different dye concentrations and pump energies is established.