Experimental observation of subluminal and superluminal light propagation in rhodamine 6G-doped polymethyl methacrylate

Nondegenerate two-wave coupling process and group velocity change in the paraxial part of an intensity-modulated and focused transverse electromagnetic beam (TEM₀₀ beam in the article) was observed in the rhodamine 6G(R6G)-doped polymethyl methacrylate (PMMA) but not in the pure PMMA. The typical superluminal result was -5.1 m/s and the subluminal result was 9.19 m/s, respectively. Furthermore, the results provide a support to our former conclusion that nondegenerate two-wave couplinglike mechanism could be used to change the group velocity of the paraxial part of a focused TEM₀₀ beam in materials with nondegenerate two-wave coupling process.