Optical quality measurements on beams generated by a stable multipass resonator and a hybrid stable–unstable resonator

Using the same radio-frequency excited slab device, we have comparatively studied two different optical schemes defining a stable multipass resonator and a hybrid stable–unstable resonator. A thorough analysis of the beams extracted from the two laser setups shows that the stable folded resonator can produce a quasi-TEM₀₀ output, at a variance with the hybrid stable–unstable resonator which always generates undesired low-power side lobes.