Transverse mode competition in a ${\mathrm{CO}}_2$ laser

Pattern formation resulting from transverse mode competition has been observed in ${\mathrm{CO}}_2$ lasers with a large transverse section and a stable near-degenerate optical cavity. The pattern properties ruled by transverse hole burning are analyzed experimentally as a function of the Fresnel number, the frequency intermode spacing, and the symmetry breaking induced by the astigmatic cavity. It is shown that mode competition imposes selection rules amid modes belonging to the largest transverse mode family allowed to oscillate. © 1996 The American Physical Society.