Photonics of laser-excited symmetric cationic polymethine dyes

Abstract

Efficient lasing is obtained in the visible and near-IR spectral regions in solutions of symmetric polymethine dyes of the indolenine series (indocyanines) pumped by the second harmonic of a Nd3+:YAG laser at 532 nm and an exciplex XeCl* laser at 308 nm into the first (long-wavelength) and higher-lying electronic absorption bands. The quantum lasing efficiency upon UV excitation achieves 37%. It is shown that these dyes can also limit the radiation power of these lasers. Polymethine dyes limit especially efficiently the second-harmonic power, their attenuation factor for the radiation power density of 100 MW cm-2 achieving 14. The nanosecond flash-photolysis study of transient absorption spectra showed that the radiation power is limited by the mechanism of reverse saturated singlet–singlet absorption. It is established that the limiting ability of polymethines strongly depends on their structure.