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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.
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Zhang et al. (2009) studied this question.
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