Ultra-low threshold lasing in silica whispering-gallery-mode microcavities with Nd3+:Gd2O3 nanocrystals

The laser performances of silica microspheres functionalized by neodymium doped gadolinium oxide nanocrystals are investigated. First, we have developed a new method to identify and selectively excite small mode volume WGMs using a tapered fiber coupler. The electromagnetic-field distribution ofWGMs is mapped by the excitation efficiency, providing a measurement of the near field intensity. Moreover a method to characterize the ultra-low threshold microlaser is presented here, which relies on the use of the thermal bistability effect: the thermal drift of the resonance line which slows down the power scanning help us to detect the onset of laser effect on the emitted light. Finally, a single mode lasing at 1088.2 nm with threshold as low as 65 nW is achieved, for a quality factor at lasing wavelength of 1.4 × 10 8 .