Visible light emission from a silica microbottle resonator by second and   third harmonic generation
  We report the first observation of nonlinear harmonic generation and sum frequency generation (SFG) coupled with stimulated Raman scattering (SRS) via the second-order (\chi^{(2)}) and the third-order (\chi^{(3)}) nonlinearities in a silica microbottle resonator. The visible light emission due to third harmonic generation (THG) was observed in both the output of a tapered fiber and the optical microscope images, which can be used to identify the axial mode profiles. SFG enabled by three- and four-wave mixing processes between the pump light and the light generated via SRS was also observed. Second Harmonic generation (SHG) and the SFG are enabled by \chi^{(2)} induced in silica by surface effects and multipole excitations. 
Motoki Asano, Shoichi Komori, Rikizo Ikuta, Nobuyuki Imoto, Sahin Kaya   Ozdemir, and Takashi Yamamoto
physics.optics