Pendant droplets have optical properties that reproduce the characteristics of
corresponding bulk materials. A particular case is the droplet hanging in air, made of a
laser dye solution and optically side-pumped. Here are shown results about laser
induced fluorescence (LIF) emitted by a single pendant droplet excited with 532 nm
pumping pulsed laser beam when its content is solution of rhodamine 6G in water kept
as such, or doped with TiO2. By changing the geometry of fluorescent medium from
bulk to pendant droplet and its volume, significant LIF changes occur. The main
difference is amplification of emitted fluorescence in pendant droplets, explained by
the confinement of light via total internal reflection in droplet. A new technique is
shown, developed to distinguish temporal changes of a droplet emission in air. It was
observed that the presence in the droplet of rhodamine 6G solution in ultrapure water
of TiO2 nanoparticles induces LIF spectra modifications depending on nanoparticles
number density and laser beam pumping energy. A concentration of 1011 part/cm3
nanoparticles favours formation of two new emission bands shifted towards blue with
respect to main band. The increase with one order of magnitude of TiO2 number
density, produces the disappearance of these bands regardless the pumping energy.
Data suggest that addition of TiO2 nanoparticles to rhodamine droplet solutions
influences emission spectra which can be modulated by varying nanoparticles
concentration and pumping beam energy.
Keywords: Fluorescence, Laser active medium, Laser dye, Laser induced
fluorescence, LIF, Lasing, Microdroplet, Nd:YAG laser, Spherical cavity,
Rhodamine 6G, Rh6G, TiO2 nanoparticles.
