Formation of a laser beam with an annular distribution of the intensity

A study was made of the conditions under which the TEM₀₁ and TEM₁₀ modes were generated simultaneously and they formed a beam with an annular distribution of the intensity. Complete suppression of the TEM₀₀ mode ensured that the ratio of the intensity at the peak of the annulus to the intensity on the axis reached 200 and it was limited by the scattering in the optical components of the resonator. A regime of mutual locking of the frequencies of the TEM₀₁ and TEM₁₀ modes was observed and then the annular beam exhibited complete spatial coherence.