Ooptical limiting properties of polymer-dye nanohybrids: a comparison between polylactide and PMMA hosts

The widespread usage of harmful pulsed laser sources emitting brief but intense radiations implies to search for appropriate and convenient forms of protection. Nonlinear optical nanomaterials can serve this purpose when properly embedded in a solid medium, resulting in nanohybrid passive optical limiting filters. This work focuses on the optical limiting behavior of polymer-dye nonlinear nanohybrids, for which we combined azophloxine, a red azo-dye, with two polymer hosts, namely PMMA and polylactide (PLA). Transmittance measurements in the nonlinear regime were performed at the wavelength of 1064 nm with nanosecond pulses at a low pulse repetition rate. The nonlinear optical properties resulting from energy dependent transmittance assessments reveal that the dye concentration is of major relevance regarding the PMMA nanohybrids, and to a lesser extend for the PLA based systems. The PLA synthesis concept described in this study offers an easy way to directly attach the dye covalently to the polymer chain. The originality and novelty of this synthesis technique is to be pointed out since it has never been mentioned elsewhere to date. For the various types of nanohybrids investigated, significant differences in the optical limiting response were observed. A molecular model claiming for the dye aggregation in the PMMA nanohybrids is discussed. Two different absorption regimes responsible for the optical limiting action have been identified to be reverse saturable – excited state absorption on the one hand and multi-photons absorption on the other hand.