Lasing action in Random Lasers made of polymers is usually achieved with a spatially distributed feedback, where scattering elements are spread over the active medium as a whole, yet some studies have shown that positive feedback may be provided from diffuse reflections at a scattering surface. Even though the latter has been demonstrated in polymeric films, it has not been shown to occur in on-chip integrated microstructures. Thus, in this paper, we demonstrate lasing action in Rhodamine B-doped polymeric microstructures whose feedback is based on diffuse reflections at the structure sidewall surfaces. The microlasers, produced by means of two-photon polymerization, are polygon-shaped on-chip microstructures featuring good structural quality and low shrinkage. The active material is Rhodamine B, which is homogeneously distributed throughout the structures. By pumping the structures with a ps-laser at 532 nm, a multi-peak emission with no evident spectral periodicity was observed. The peaks are a result of successive diffuse reflections of light at the structure sidewall surfaces that re-enters the gain medium and closes feedback loops with different perimeters and Q-factors. In spite of their omnidirectional emission, the microstructures lasing threshold was found to be on the order of nanojoules, which is comparable to what had been reported for microlasers based on optical resonators. This work therefore provides an easy way of realizing low-threshold random microlasers that hold potential as a solid-state laser source for integrated optics applications

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Nathália B. Tomazio, Lucas F. Sciuti, Gustavo F. B. Almeida, Leonardo De Boni, and Cleber R. Mendonça, "Dye-doped random microlasers fabricated via femtosecond laser-induced two-photon polymerization (Conference Presentation)," Proc. SPIE 10915, Organic Photonic Materials and Devices XXI, 109150W (Presented at SPIE OPTO: February 07, 2019; Published: 5 March 2019); https://doi.org/10.1117/12.2507650.6010444353001.