Using linearly polarized dye laser beam which is tuned between the doublet on Na to excite Na vapor, a conical emission with polarization perpendicular to that of the incident laser in the forward direction has been observed. Its spectrum and the time evolution are measured. The relation between this emission and the density of Na, the parameters of laser and the pressure of the buff re gas have been studied. This phenomena may be explained by considering the coupling of Rayleigh scattering and transient field of Na atom.