Abstract

We will report on a close analogy between turbulent convection in large aspect ratio fluids and traveling wave turbulent patterns in lasers with wide gain sections. In contrast to the fluid case, exact traveling wave solutions can be easily derived for the Maxwell-Bloch equations, including diffraction effects. As in the fluid case, we can identify regions in physical parameter space where stable traveling wave and turbulent patterns can coexist. For a two-level laser, the stable traveling wave region (Busse balloon) extends down to the first laser threshold. However, the Busse balloon for a Raman laser may lie well above the instability threshold or may extend down to the first laser threshold, depending on the sign of the intermediate level detuning from the pump. The physical manifestation of these stable traveling wave solutions is a controllable off-axis far-field emission of the laser. The onset of turbulent patterns beyond the first threshold in the Raman laser is caused by a sideband instability occurring at right angles to the underlying traveling wave (roll) solution. This instability causes the spontaneous nucleation of defects from finite amplitude solutions.

© 1992 Optical Society of America