Laser beam quality versus aperture size in a cw argon-ion laser

Abstract

The measured beam quality of a typical argon-ion laser that uses a stable resonator is found to be slightly greater than unity for small intracavity aperture sizes, approaching M2 ≈ 1 as the mode-control aperture diameter is increased. Above a critical aperture size, the beam quality suddenly deteriorates, however, rising toward M2 ≈ 2 for larger apertures, although it is difficult to detect the onset of this deterioration from observations of either the laser output power or the output beam profile. Computer simulations confirm that the sudden rise in the M2 factor is due to the onset of a higher-order donut mode that oscillates simultaneously with the fundamental TEM00 mode. This general behavior is characteristic of other types of stable-cavity gas laser as well.