Abstract

Most nonlinear dynamic studies of optical systems in the recent past have focused on temporal behavior of the output radiation.¹ However, recent theoretical studies² have predicted the emergence of spatiotemporal structures and of a new frequency locking effect in a number of passive and active optical systems. Here we present experimental evidence in support of these effects using a CO₂ laser with a simple intracavity arrangement that allows the continuous variation of the radius of curvature of the output couplers and, therefore, of the radial mode spacing. When the frequency spacing between consecutive transverse modes is sufficiently small, complex stationary spatial patterns develop in qualitative agreement with the theoretical predictions, and the laser oscillates with radial modes synchronously locked to each other. For larger values of the radial spacing, the frequency locking is lost and the transverse modes tend to operate more independently of one another, as evidenced by the appearance of beating effects in the output signal. The loss of frequency locking also corresponds to a reduction of the average power output. A further increase in the radial mode spacing eventually leads to the standard TEM₀₀ mode configuration.

© 1988 Optical Society of America