Abstract

Two types of conical emission in sodium have appeared in the past. In the first, a single tightly focused laser beam is tuned to the blue side of the D1 line in conditions compatible with self-trapping. The emission is specular, has a cone half-angle of a degree, and occurs on the red side of line center. In the second type, two weakly focused counterpropagating laser beams are tuned to the red side of line center. The emission consists of radial filaments, has a cone half-angle of 8°, and is the same wavelength as the pumps. We report on yet a third type of conical emission which is distinct from the first two types by virtue of its spatial and spectral characteristics. Like the first type, the pumps are tuned to the blue side of line center, the emission has a cone half-angle of a degree and is specular. However, this phenomenon also resembles the second type of conical emission in that two counterpropagating pumps are required, the pumps are weakly focused, and the emission wavelength is the same as the pumps.

© 1987 Optical Society of America