Whispering gallery mode assisted random lasing in dye-doped PVA coated silica microsphere

We explore whispering gallery mode (WGM) assisted random lasing under circular spot excitation from a 4- (dicyanomethylene)-2-methyl-6-(4dimethylaminostyryl)-4h-pyran (DCM) dye-doped poly(vinylalcohol) (PVA) thin film coated silica microsphere when excited above the threshold excitation intensity. The output spectrum consists of randomly positioned narrow spectral lines. Under circular spot-excitation, the allowed WGMs in the microcavity provide a stripe like path along the equator for amplification. The high-power density built within these microcavities due to WGM and the weakly scattering random lasing effect, along with stripe like excitation combined with the high fluorescence quantum yield of DCM dye, give rise to threshold pump energies as low as 33 μJ for free space pulsed excitation at 532 nm. This makes these DCM-PVA coated microspheres attractive tiny sources for sensing applications.