Strong Mode Selection Scheme in a Layered Cylindrical Microcavity Laser with a Thin Dielectric Inner Coating

We investigated strong mode selection scheme in a layered cylindrical microcavity laser with a thin lower refractive dielectric inner coating. We used a fused silica capillary (outer diameter of 320 mum, inner diameter of 250 mum), filled with dye-doped ethanol, as the cylindrical cavity and coated AF 1600 on the inner wall of the capillary in order to change the reflectivity of light at the inner wall. Because whispering gallery modes perturbed (or split) by inner wall, there exist interferential coupling effect whose modulation depth depends on the reflectivity of inner wall. The strongest mode selection was observed at the reflectivity of about 50%, in which corresponding thickness of AF 1600 was about 0.4 mum. Due to the enhanced interferential coupling effect, the lasing spectrum appeared as few periodic peaks just around the wavelengths corresponding to the constructive interference condition. We compared the lasing spectrum with that from a bare capillary and discussed the role of thin dielectric coating on the strong mode selection.