Generation of light in the near infrared using solutions of asymmetric polymethine dyes

It is shown that efficient lasing is possible in the near infrared if the active medium is a liquid solution of a polymethine dye with a strong intramolecular electronic asymmetry. In contrast to symmetric polymethine dyes, lasing is characterized by a large red shift so that it is possible to use visible radiation (second harmonic of a YAG:Nd³⁺ laser or argon and copper laser radiations) for the purpose of pumping. These dyes interact with a polar solvent forming in the ground state two groups of centers of specific and nonspecific solvation. A short-wavelength center of specific solvation transforms, in an excited state, to a nonspecific solvation center retaining the electronic excitation and it can therefore emit fluorescence or amplify radiation. The efficiency of this process is high so that the lasing efficiency in the range 750–850 nm (when pumping is provided at 532 nm) reaches 10–15%.