Bio-inspired random lasers enabled by poplar catkin microstructures

This work presents a random laser (RL) based on natural biomaterials, specifically poplar catkin fibers (PCFs), used as a biodegradable scattering matrix in a solution-processed gain medium with Rhodamine 6G. Five samples with PCF concentrations ranging from 1.5 to 5.5 mg/mL were prepared, and the lasing threshold reached a minimum of 8.21 µJ/pulse at 4.5 mg/mL-attributed to optimal multiple scattering provided by the hierarchical fibrous network. At this concentration, the emission spectrum narrowed from 14.8 nm to 0.8 nm at 584 nm, accompanied by nonlinear intensity growth and a 4 nm redshift from lower concentrations, indicating enhanced scattering strength. The system maintained stable output over 1,200 pump pulses, and replica symmetry breaking analysis confirmed the emergence of reproducible coherent modes above threshold. Owing to its low spatial coherence, the device achieved a speckle contrast of only 0.0755-significantly lower than that of a conventional 532 nm laser (0.2118)-enabling high-fidelity speckle-free imaging of both a USAF 1951 target and a dragonfly wing. This work establishes PCFs as a green, low-cost, and high-performance RL platform, offering a promising route toward speckle-free imaging applications in bioimaging, environmental sensing, and flexible photonics.