“…Such conical emission (CE) has been observed at wavelengths near that of the incident laser light (see, e.g., [13,14,15,16,17] and references therein) and also at wavelengths corresponding to other atomic transitions [9,10,11,12]. Collimated light (light emitted in a filled-in cone with relatively small angle of divergence compared to CE) can be generated in both the forward and backward directions with respect to the propagation direction of incident laser light (see, e.g., [1] and references therein).…”