Axial and radial random lasing in a biopolymer based liquid core ring resonator

Abstract

Tunable random lasing from a liquid core cylindrical microcavity by transversely pumping a silica capillary filled with a BSA (Bovine Serum Albumin)-Rhodamine B (RhB) composite biopolymer solution is reported. The binding of RhB to discrete sites of BSA mediates the structural arrangement of lasing species, influencing the stimulated emission and tunability. The UV–Vis, Photoluminescence (PL), FTIR spectroscopy and molecular docking studies were used to analyze the dye binding with BSA. Laser emission was collected from the surface as well as the end of the capillary upon transverse pumping along its length. The optical feedback from the cavity effects of the cylindrical microstructure enhances the random lasing modes. Lasing threshold and red shift in the emission were found to be tunable with BSA concentrations. The surface emissions were characterized by sharp and distinct lasing peaks at low thresholds in contrast to the relatively broad end emissions requiring a four-fold pump pulse energy at a BSA concentration of 0.6 g/ml. This difference in lasing threshold is in agreement with the Power Fourier Transform (PFT) analysis of the surface and end emissions. The cavity path lengths corresponding to the surface and end emissions were analyzed and the shorter path length for surface emissions favours the formation of coherent loops of photons and a lower lasing threshold. The coexistence of surface and end emissions with entirely different characteristics from the capillary and its tunability opens up new avenues in the development of biomaterial-based integrated light sources for sensing, display technology and encryption.