Concave–Convex Resonator

The pertinent beam parameters for concave–convex resonators can be calculated if we introduce a negative radius (−R₂) for the convex mirror into (1)–(2).

..........(1)

.......(2)

A small-radius convex mirror in conjunction with a large-radius concave or plane mirror is a very common resonator in high-average-power solid-state lasers. As follows from the discussion in the next section, as a passive resonator such a configuration is unstable. However, in a resonator that contains a laser crystal, this configuration can be stable since the diverging properties of the concave mirror are counteracted by the focusing action of the laser rod. Since the concave mirror partially compensates for thermal lensing, a large mode volume can be achieved