Remarkable optical properties of dendrimers for laser applications

We have investigated optical properties of dye-encapsulated dendrimers for photonic applications and observed several interesting behavior, such as controlled intermolecular interactions, super-radiance, and supernarrowing laser emission. We confirmed limited inter molecular interactions between encapsulated dyes in fluorescence lifetime measurement of rhodamine B-cored dendrimers with different shell sizes. Also, photochemical stability against singlet oxygen was studied for fluorescent dyes encapsulated in a dendrimer box and the lifetime was improved by 60 times due to the shielding effect of the dendrimer shell. A supernarrowing laser spectrum was observed without using any resonator mirrors due to moderate scattering caused by densely doped dendrimer aggregates in a polymer waveguide. At the optimum operation level, the spectral linewidth is found to be 0.55 rim, which is limited by the resolution of the spectrograph used. Weak scattering from the aggregated dendrimers in the host polymer matrix with gain is responsible for photon localization. However, in contrast to conventional random lasers with strong scattering, weak scattering enables the long amplification path through the waveguide producing a directional beam and a supernarrowing spectrum. The dependence of supernarrowing lasing behavior on the density of the scattering moiety was studied by changing the dendrimer doping ratios in the polymer matrix.