Observation of tunable superluminal propagation in the single-layer graphene oxide solution

The author observed superluminal phenomena in the transparent single-layer graphene oxide (GO) solution and studied the relationship between the advance time and the solution concentration or the power of the incident light. We learned that the time advancement can be modulated in a wider range by increasing the light power; both the group velocity and the time advancement decay nonlinearly as a function of the modulation frequency, which depends on the concentration of the GO solution and the power of the incident light.