Fluorescence and Time-Delayed Lasing during Single Laser Pulse Excitation of a Pendant mm-Sized Dye Droplet

Abstract

Fluorescence and lasing emission that are produced separately in time during excitation laser pulse for an mm-sized Rhodamine 6G dye-water droplet are reported. The droplet acts as a quasi-spherical closed optical resonator and due to multiple internal reflections, the resonant amplified emission is delayed with respect to fluorescence emission. Measurements of the temporal evolution of the droplet’s emission were performed by varying the signal acquisition gate width and gate delay with respect to the pumping pulse. The droplet emission spectra are structured in two bands which appear one after the other in time: first, the fluorescence emission band which follows pumping laser pulse time shape and then a second band, the lasing band, placed at shorter wavelengths and formed in time after the peak of the pumping laser pulse intensity, on the pulse tail. The lasing threshold pumping intensity is much lower than those for typical dye lasers.

Cavity-Enhanced Fluorescence in Colliding Droplets of Rhodamine 6G Aqueous Solutions

“…Similarly, in Figure 3b, the peaks blue-shifted with increased laser power because of decreased reabsorption at short wavelengths by increased fluorescence intensity. 33 Thus, the fluorescence propagated and gained intensity via resonance and decreased reabsorption.…”

Spectral Properties of Foams and Emulsions

“…In some cases, emission is produced by the interaction of the light beams with droplets' materials, and in others, with the droplets' environment materials. Both processes contribute to the increase in the intensity of the emitted signals [8,10,11]. These characteristics are useful, since they allow, for instance, to identify the producers of the spectral effects at lower concentrations, down to traces, based on their molecular signatures.…”

Editorial: Trends in Optical/Laser Spectroscopy and Applications

“…This is complementary, at the opposite geometrical scale, to the laser physics that uses extremely large laser systems emitting tens of Petawatt (PW, 1PW = 10 15 Watt) laser beams [ 3 ]. A typical laser in this category is the microlitre droplet laser, which uses as its active medium a droplet of liquid optically pumped with another laser beam [ 4 , 5 , 6 , 7 ]. Since a laser beam is used for droplet pumping, a controlled match should be made of the beam power (i.e., laser beam pressure) with the absorption of the droplet’s material (i.e., absorbent concentration) [ 8 ].…”