Photoinduced Localized Phonons and Instantaneous Structure Contributing to Amplified Spontaneous Emission of Conjugated Polymers

Amplified spontaneous emission (ASE), as a microscopic dynamical process, significantly influences the quality of optically pumped conjugated polymeric lasers. Based on the continuous optical pumping that couples with the prominent self-trapping process of conjugated polymer, four localized phonon modes are distinguished in conjugated polymers, all of which greatly contribute to localization of the excited state as well as local distortion along alternating single and double bonds. Consequently, the ultrafast localized distortion of alternating bonds constructs “instantaneous” structures—an effective four-level electronic structure and population inversion—for ASE. It is shown that all the evolving localized vibrational modes possess even parity, which not only makes it highly possible to be probed through the infrared phonon spectrum, but also opens up an opportunity to improve the quantum efficiency of a polymer ASE/laser by modification of localized phonon modes.