An ultrahigh-Q microsphere laser based on the evanescent-wave-coupled gain

We have demonstrated an ultrahigh-Q whispering-gallery-mode (WGM) microsphere laser based on the evanescent-wave-coupled gain. Dye molecules outside the sphere near the equator were excited, resulting in WGM lasing in the lowest radial mode order. The loaded quality factor of the lasing WGM was 8(2)\times 10^9, the highest ever achieved in the microlaser.