Resonant Interaction of Laser Beams with Pendant Droplets

Resonant interaction of a laser beam with a single droplet takes place if the beam is absorbed in the droplet. Results are shown regarding the resonant interactions of pulsed laser beams with microliter droplets in pendant position which contain solutions of a laser dye-rhodamine 6G, phenothiazines (chlorpromazine, promazine), hydantoin derivative [(5Z)-5-(3-chlorobenzylidene)-2-thioxo-4-imidazolidinone)] and antibiotics (vancomycin), respectively, in water. A description of the electronic structure of rhodamine 6G and chlorpromazine using Gaussian09 and GaussView 5.0 software is made. Exposure of droplets to laser radiation leads to generation of new photoproducts that may have different properties if compared to parent compounds. Such modifications are evidenced by laser induced fluorescence and thin layer chromatography. In irradiated chlorpromazine water solution, out of hundreds of photoreaction products, 5 were identified: promazine (PZ), promazine sulfoxide (PZ-SO), 2-hydroxy promazine (PZ-OH), 2-hydroxy promazine sulfoxide (PZ-OH-SO), chlorpromazine sulfoxide (CPZ-SO). For rhodamine 6G solutions, the main results include the increasing intensity of LIF spectra in droplet with respect to bulk, even if the volume of the cuvette for bulk measurements is much higher than droplet’s volume. This behaviour may be explained by the confinement of light inside droplet, where total internal reflection at surface occurs, the droplet being associated with a spherical micro-optical resonator.

Keywords: Chlorpromazine, Droplet, Fluorescence, Hydantoins, Laser dye, Lasing, Laser induced fluorescence, Promazine, Rhodamine 6G, Vancomycin, Whispering gallery modes, WGM.