Ultralow threshold laser action from toroidal polymer microcavity

We report laser action from a toroidal microcavity coated with pi-conjugated polymer. An ultralow threshold value of similar to 200 pJ/pulse is achieved by free space excitation in ambient conditions. This is the lowest threshold energy obtained in microtoroid lasers by free space excitation. The effective refractive index of the polymer, extracted from Fourier analysis of emission spectra, is 1.787, which is very close to measured value of 1.790 indicating that laser modes are located around the circumference of the cavity as whispering gallery resonances.