Evidence that transverse effects cause an instability in a single-mode CO2 laser

We show experimental evidence of spontaneous oscillations in a single-transverse and single-longitudinal mode CO2 laser under conditions for which the plane-wave Maxwell-Bloch model predicts stable laser operation. These instabilities seem to result from transverse structure in the mode, as a model which accounts for the transverse profile of the field in the cavity predicts behavior in close agreement with our experimental results. © 1987 The American Physical Society.