Low-threshold and stable coherent random lasing based on mesoporous silica nanoparticles in a capillary glass tube

Random lasers (RLs) depending on disordered feedback mechanisms, offer unique advantages in low spatial coherence and miniaturization but face challenges in achieving low thresholds and stability. This study demonstrates a mesoporous silica nanoparticle (MSN)-based RL system for coherent, low-threshold lasing, which shows a typical replica symmetry breaking (RSB) phenomenon. By surfactant-templated methods, the synthesized MSNs exhibit uniform spherical morphology of 200 nm in diameter with hierarchical mesopores of 5-10 nm, achieving high dye loading efficiency and enhanced photon scattering, critical for realizing efficient disordered feedback. By optimizing the MSN and dye concentration at 3 mg/mL and 4 mg/mL, respectively, corresponding with the scatters and gain medium, we inhibit the possible photodegradation of the dye molecules adsorbed on the MSN surface. Thus, a low lasing threshold of 16.6 µJ/mm² is achieved. As the pump energy is incrementally increased from below-threshold to near-threshold and subsequently to above-threshold levels, a distinct transition is observed in the intensity fluctuations of the emitted light, shifting from a Gaussian-distributed photonic paramagnetic state to a symmetry-broken spin-glass state. Multimode spectral evolution under high pump fluence is attributed to disordered photon resonant loops, while 3000-cycle continuous pumping tests confirm robust emission characteristics. Speckle contrast measurements reveal superior speckle-free imaging quality compared to conventional lasers. These results establish MSNs as a monolithic platform for low-threshold, speckle-suppressed lasers, advancing applications in biomedical imaging and integrated photonic devices.