Directly Pumped Ho3+-Doped Microspheres Lasing at $2.0~\mu$ m

Directly pumped single-mode and multimode Ho
³⁺
-doped sol-gel silica microspheres lasing at 2.0 μm are observed, when an 1150-nm fiber Raman laser pump is used in a conventional microfiber-microsphere coupling method. Experimental results show single-mode output at 2 μm as well as the characteristic whispering-gallery-mode (WGM). By adjusting the taper contact position on the microsphere, we achieved switching between single-mode and multimode laser operations.