Multimode emission of fluorinated ethylene propylene clad large diameter liquid-core lasers

Abstract

A liquid-core (LiCo) dye laser was demonstrated using Rhodamine B (RhB) dissolved in glycerol as the gain medium and fluorinated ethylene propylene (FEP) tubing as the waveguide. Photoluminescence and amplified spontaneous emission (ASE) studies identified optimal RhB concentrations of 0.1 wt.% and 0.3 wt.% for low-threshold laser operation. Laser emission was achieved in LiCo rods with 1/16 inch and 1/32 inch inner diameter FEP tubing, with narrower tubing providing enhanced mode confinement and spectral narrowing. The addition of cavity mirrors improved emission coherence, revealing a distinct laser mode at low pump energies with mode spacing inconsistent with a simple Fabry-P\'erot cavity, indicating complex mode coupling and internal reflections. Limitations include spectral broadening and scattering-induced parasitic feedback, which suggest avenues for further optimization in waveguide materials and output coupling.