Distributed Feedback Lasing in Amorphous Polymers with Covalently Bonded Fluorescent Dyes: The Influence of Photoisomerization Process
Résumé
We present the synthesis and characterization of a new type of organic materials for light amplification purposes. These materials consist in branched polymers based on 9,10-bis(4-(diethylamino)phenylethynyl)anthracene or 2-(3-(4-(diethylamino)styryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile chromophore cores with covalently attached poly(methyl methacrylate) chains, named Ant-PMMA and Lem-PMMA, respectively. In both cases, polymers with controlled molecular weight of about 30 kDa were synthesized by atom transfer radical polymerization (ATRP), using functionalized chromophores as initiators. Thin layers of the two polymers were fabricated by a simple drop-casting technique. We describe the spectroscopic properties of these materials and their ability for light amplification through the measurements of amplified spontaneous emission, random lasing process, and distributed feedback (DFB) lasing achieved via holographic-type excitation. Considering the different chemical structures of the chromophores, and related distinct interaction pathways with light, we postulate two slightly different DFB lasing mechanisms in investigated organic solid-state gain media. The Lem-PMMA ability to undergo photoisomerization, providing material refractive index modulation upon holographic-type pumping, is supposed to be responsible for superior DFB lasing performance as compared to Ant-PMMA, for which similar type of excitation results in lasing coupling solely dominated by gain modulation.