The nonlinear optical effect and group velocity control in Pu-erh tea solution
普洱茶的非线性光学效应与光速调控

The nonlinear optical effect of the Pu-erh tea solution of water was studied by Z-scan technique, and a high nonlinear refractive index was found with continuous laser, which was six orders of magnitude larger than that of CS2. Especially, a conversion from subluminal light to superluminal light was observed in our sample, which demonstrates that the controlling of the group velocity of light based on the dispersive effect of phase coupling is applicable widely to nonlinear materials.