Abstract
We investigate the whispering gallery modes (WGMs) of self-assembled single microspheres. They consist of a recently developed highly fluorescent π-conjugated copolymer and exhibit excellent optical properties with Q-factors up to 104. Under continuous laser irradiation, we observe a splitting of the highly degenerate spherical WGMs into a multiplet of lines. Comparison with the calculated spectral response of a weakly distorted sphere shows that the optical excitation induces a change of the optical path length in the microcavity so that it resembles a prolate spheroid. The separation of the lines is given by the ellipticity and the azimuthal mode number. Measurements in various gaseous environments suggest that the distortion is caused by light induced oxidation of the polymer. Our findings show that photooxidation can be a beneficial mechanism for in-situ tuning of optically active polymer structures.
Highlights
Our findings show that self-assembled π-conjugated polymer spheres can have excellent optical properties, which are in-situ tunable
The polymer was dissolved in chloroform (0.5 mg/mL) and methanol vapour was gradually diffused into the solution
The resulting dispersion was drop cast onto quartz glass substrates (η = 1.46) and dried under vacuum
Summary
Our findings show that self-assembled π-conjugated polymer spheres can have excellent optical properties, which are in-situ tunable. This makes them versatile building blocks for more sophisticated optically active structures, such as coupled resonators, photonic crystals, sensors, and detectors.
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