Whispering-Gallery-Mode for Coherent Random Lasing in a Dye-Doped Polystyrene Encapsulated Silica-Glass Capillary

Dye-doped polystyrene (DDPS) encapsulated in a silica-glass capillary with a diameter of 300 mu m was fabricated through radical polymerization of styrene within the capillary. The coherent random lasing (RL) with full width at half maximum (FWHM) of 0.36 nm and a quality factor of 1608 was produced in the DDPS with the capillary when pumping at 532 nm. However, the incoherent RL with FWHM of 6.62 nm and a quality factor of 92 was produced in the DDPS without the capillary. A detailed investigation on this phenomenon by changing the diameter of the capillary and core refractive index (RI) reveals that there exists a strong whispering gallery mode (WGM) resonance in the capillary, which helps generate the coherent RL. The findings may open up a new approach for the fabrication of highly efficient photonic devices.