Dynamical study on the stimulated processes of an exciton and a biexciton in a polymer

• Stimulated emission and absorption take place with the same probability in an exciton.
• Formation mechanism of biexciton about the re-excitation of an exciton is confirmed.
• There exist two different modes for the stimulated emission of a biexciton.
• By both of the two modes, we can get a light amplification.
• The results are helpful for further improving the optical applications of polymers.

By applying a femtosecond stimulating pulse, we theoretically study the stimulated processes of an exciton and a biexciton in a polymer within the framework of an extended Su–Schrieffer–Heeger tight-binding model. For an exciton, it is obtained that the stimulated emission and absorption between the intragap levels take place with the same probability, by which we will not get the light amplification. However, the light amplification can be realized by the stimulated emission between the intragap levels in a biexciton, which is found to have two different modes. Finally, effect of the stimulating energy and intensity on the stimulated processes is separately analyzed. These results might be of great importance for further improving the optical applications of polymers, especially for optimizing the polymer laser properties.